draft-ietf-nfsv4-rfc3530-migration-update-07.txt   draft-ietf-nfsv4-rfc3530-migration-update-08.txt 
NFSv4 D. Noveck, Ed. NFSv4 D. Noveck, Ed.
Internet-Draft HP Internet-Draft HPE
Updates: 7530 (if approved) P. Shivam Updates: 7530 (if approved) P. Shivam
Intended status: Standards Track C. Lever Intended status: Standards Track C. Lever
Expires: January 4, 2016 B. Baker Expires: August 4, 2016 B. Baker
ORACLE ORACLE
July 3, 2015 February 1, 2016
NFSv4.0 migration: Specification Update NFSv4.0 migration: Specification Update
draft-ietf-nfsv4-rfc3530-migration-update-07 draft-ietf-nfsv4-rfc3530-migration-update-08
Abstract Abstract
The migration feature of NFSv4 allows for responsibility for a single The migration feature of NFSv4 allows for responsibility for a single
filesystem to move from one server to another, without disruption to file system to move from one server to another, without disruption to
clients. Recent implementation experience has shown problems in the clients. Recent implementation experience has shown problems in the
existing specification for this feature in NFSv4.0. This document existing specification for this feature in NFSv4.0. This document
clarifies and corrects RFC7530 (the NFSv4.0 specification) to address identifies the problem areas and provides revised specification text
these problems. which updates the NFSv4.0 specification in RFC7530.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 4, 2016. This Internet-Draft will expire on August 4, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Client Identity Definition . . . . . . . . . . . . . . . . . 5 3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Differences from Replaced Sections . . . . . . . . . . . 5 3.2. Data Type Definitions . . . . . . . . . . . . . . . . . . 5
4.2. Client Identity Data Items . . . . . . . . . . . . . . . 5 4. Background . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Server Release of Client ID . . . . . . . . . . . . . . . 9 5. Client Identity Definition . . . . . . . . . . . . . . . . . 7
4.4. Client Id String Approaches . . . . . . . . . . . . . . . 10 5.1. Differences from Replaced Sections . . . . . . . . . . . 7
4.5. Non-Uniform Client Id String Approach . . . . . . . . . . 12 5.2. Client Identity Data Items . . . . . . . . . . . . . . . 8
4.6. Uniform Client Id String Approach . . . . . . . . . . . . 13 5.2.1. Client Identity Structure . . . . . . . . . . . . . . 8
4.7. Mixing Client Id String Approaches . . . . . . . . . . . 14 5.2.2. Client Identity Shorthand . . . . . . . . . . . . . . 10
4.8. Trunking Determination when Using Uniform Client Id 5.3. Server Release of Client ID . . . . . . . . . . . . . . . 13
Strings . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.4. Client Id String Approaches . . . . . . . . . . . . . . . 13
4.9. Client Id String Construction Details . . . . . . . . . . 22 5.5. Non-Uniform Client Id String Approach . . . . . . . . . . 15
5. Locking and Multi-Server Namespace . . . . . . . . . . . . . 23 5.6. Uniform Client Id String Approach . . . . . . . . . . . . 16
5.1. Lock State and Filesystem Transitions . . . . . . . . . . 24 5.7. Mixing Client Id String Approaches . . . . . . . . . . . 18
5.1.1. Migration and State . . . . . . . . . . . . . . . . . 24 5.8. Trunking Determination when Using Uniform Client Id
5.1.1.1. Migration and Clientid's . . . . . . . . . . . . 26 Strings . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1.1.2. Migration and State Owner Information . . . . . . 27 5.9. Client Id String Construction Details . . . . . . . . . . 26
5.1.2. Replication and State . . . . . . . . . . . . . . . . 31 6. Locking and Multi-Server Namespace . . . . . . . . . . . . . 27
5.1.3. Notification of Migrated Lease . . . . . . . . . . . 31 6.1. Lock State and File System Transitions . . . . . . . . . 28
5.1.4. Migration and the Lease_time Attribute . . . . . . . 33 6.1.1. Migration and State . . . . . . . . . . . . . . . . . 28
6. Server Implementation Considerations . . . . . . . . . . . . 34 6.1.1.1. Migration and Client IDs . . . . . . . . . . . . 30
6.1. Relation of Locking State Transfer to Other Aspects of 6.1.1.2. Migration and State Owner Information . . . . . . 31
Filesystem Motion . . . . . . . . . . . . . . . . . . . . 34 6.1.2. Replication and State . . . . . . . . . . . . . . . . 35
6.2. Preventing Locking State Modification During Transfer . . 36 6.1.3. Notification of Migrated Lease . . . . . . . . . . . 35
7. Additional Changes . . . . . . . . . . . . . . . . . . . . . 39 6.1.4. Migration and the Lease_time Attribute . . . . . . . 38
7.1. Summary of Additional Changes from Previous Documents . . 39 7. Server Implementation Considerations . . . . . . . . . . . . 39
7.2. NFS4ERR_CLID_INUSE definition . . . . . . . . . . . . . . 40 7.1. Relation of Locking State Transfer to Other Aspects of
7.3. NFS4ERR_DELAY return from RELEASE_LOCKOWNER . . . . . . . 40 File System Motion . . . . . . . . . . . . . . . . . . . 39
7.4. Operation 35: SETCLIENTID - Negotiate Client ID . . . . . 41 7.2. Preventing Locking State Modification During Transfer . . 40
7.5. Security Considerations for Inter-server Information 8. Additional Changes . . . . . . . . . . . . . . . . . . . . . 44
Transfer . . . . . . . . . . . . . . . . . . . . . . . . 45 8.1. Summary of Additional Changes from Previous Documents . . 44
7.6. Security Considerations Revision . . . . . . . . . . . . 45 8.2. NFS4ERR_CLID_INUSE definition . . . . . . . . . . . . . . 45
8. Security Considerations . . . . . . . . . . . . . . . . . . . 45 8.3. NFS4ERR_DELAY return from RELEASE_LOCKOWNER . . . . . . . 45
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46 8.4. Operation 35: SETCLIENTID - Negotiate Client ID . . . . . 46
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 8.5. Security Considerations for Inter-server Information
10.1. Normative References . . . . . . . . . . . . . . . . . . 46 Transfer . . . . . . . . . . . . . . . . . . . . . . . . 50
10.2. Informative References . . . . . . . . . . . . . . . . . 46 8.6. Security Considerations Revision . . . . . . . . . . . . 50
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 46 9. Security Considerations . . . . . . . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 51
11.1. Normative References . . . . . . . . . . . . . . . . . . 51
11.2. Informative References . . . . . . . . . . . . . . . . . 51
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
1. Introduction 1. Introduction
This document is a standards track document which corrects the This document is a standards track document which corrects the
existing definitive specification of the NFSv4.0 protocol, in existing definitive specification of the NFSv4.0 protocol, in
[RFC7530]. Given this fact, one should take the current document [RFC7530]. Given this fact, one should take the current document
into account when learning about NFSv4.0, particularly if one is into account when learning about NFSv4.0, particularly if one is
concerned with issues that relate to: concerned with issues that relate to:
o Filesystem migration, particularly when it involves transparent o File system migration, particularly when it involves transparent
state migration. state migration.
o The construction and interpretation of the nfs_clientid4 structure o The construction and interpretation of the nfs_client_id4
and particularly the requirements on the id string within it, structure and particularly the requirements on the id string
referred to below as a "client id string". within it, referred to below as a "client id string".
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Background 3. Definitions
3.1. Terminology
The following definitions are provided for the purpose of providing
an appropriate context for the reader. This section is derived from
Section 1.5 of [RFC7530] but has been adapted to the needs of this
document.
Boot instance id: A boot instance id, is an identifier, such as a
boot time, allowing two different instances of the same client to
be reliably distinguished. A boot instance id is opaque to the
server and is often used as the verifier field in the
nfs_client_id4 structure which identifies the client to the
server.
Client: A client is an entity that accesses the NFS server's
resources. The client may be an application that contains the
logic to access the NFS server directly. The client may also be
the traditional operating system client that provides remote file
system services for a set of applications.
With reference to byte-range locking, the client is also the
entity that maintains a set of locks on behalf of one or more
applications. This client is responsible for crash or failure
recovery for those locks it manages.
Note that multiple clients may share the same transport and
connection, and multiple clients may exist on the same network
node.
Client ID: A client ID is a 64-bit quantity (in the form of a
clientid4) used as a unique, shorthand reference to particular
client instance, identified by client-supplied verifier (in the
form of a boot instance id) and client id string. The server is
responsible for supplying the client ID.
File System: A file system is the collection of objects on a server
that share the same fsid attribute (see Section 5.8.1.9 of
[RFC7530]).
Grace period: A grace period is an interval of time during which the
server will only grant locking requests to reclaim existing locks
but not those which create new locks. This give clients an
opportunity to re-establish locking state in response to a
potentially disruptive event. The grace period may be general, to
help deal with server reboot, or file-system-specific, to deal
with file system migration when transparent state migration is not
provided.
Lease: A lease is an interval of time defined by the server for
which the client is irrevocably granted a lock. At the end of a
lease period the lock may be revoked if the lease has not been
extended. The lock must be revoked if a conflicting lock has been
granted after the lease interval.
All leases granted by a server have the same fixed duration. Note
that the fixed interval duration was chosen to alleviate the
expense a server would have in maintaining state about variable-
length leases across server failures.
Lock: The term "lock" is used to refer to record (byte-range) locks
as well as share reservations unless specifically stated
otherwise.
Lock-Owner: Each byte-range lock is associated with a specific lock-
owner and an open-owner. The lock-owner consists of a client ID
and an opaque owner string. The client presents this to the
server to establish the ownership of the byte-range lock as
needed.
Open-Owner: Each open file is associated with a specific open-owner,
which consists of a client ID and an opaque owner string. The
client presents this to the server to establish the ownership of
the open as needed.
Server: A server is an entity responsible for coordinating client
access to a set of file systems.
Stateid: A stateid is a 128-bit quantity returned by a server that
uniquely identifies the open and locking states provided by the
server for a specific open-owner or lock-owner/open-owner pair for
a specific file and type of lock.
Trunking: A situation in which multiple physical addresses are
connected to the same logical server.
Verifier: A verifier is a quantity, in the form of a verifier4, that
allows one party to an interaction to be aware of a re-
initialization or other significant change to the state of the
other party. In [RFC7530], this term most often designates the
verifier field of an nfs_client_id4, in which a boot instance id
is placed to allow the server to determine when there has been a
client reboot, making it necessary to eliminate locking state
associated with the previous instance of the same client.
3.2. Data Type Definitions
This section contains a table which shows where data types referred
to in this document are defined.
+-----------------+------------------------------+
| Item | Section |
+-----------------+------------------------------+
| cb_client4 | Section 2.2.11 in [RFC7530] |
| clientaddr4 | Section 2.2.10 in [RFC7530] |
| clientid4 | Section 2.1 in [RFC7530] |
| lock_owner4 | Section 2.2.14 in [RFC7530] |
| nfs_client_id4 | Section 5.2.1 |
| open_owner4 | Section 2.2.13 in [RFC7530] |
| verifier4 | Section 2.1 in [RFC7530] |
+-----------------+------------------------------+
4. Background
Implementation experience with transparent state migration has Implementation experience with transparent state migration has
exposed a number of problems with the then-existing specifications of exposed a number of problems with the then-existing specifications of
this feature, in [RFC7530] and predecessors. The symptoms were: this feature, in [RFC7530] and predecessors. The symptoms were:
o After migration of a filesystem, a reboot of the associated client o After migration of a file system, a reboot of the associated
was not appropriately dealt with, in that the state associated client was not appropriately dealt with, in that the state
with the rebooting client was not promptly freed. associated with the rebooting client was not promptly freed.
o Situations can arise whereby a given server has multiple leases o Situations can arise whereby a given server has multiple leases
with the same nfs_client_id4 (id and verifier), when the protocol with the same nfs_client_id4 (consisting of id and verifier
clearly assumes there can be only one. fields), when the protocol clearly assumes there can be only one.
o Excessive client implementation complexity since clients have to o Excessive client implementation complexity since clients have to
deal with situations in which a single client can wind up with its deal with situations in which a single client can wind up with its
locking state with a given server divided among multiple leases locking state with a given server divided among multiple leases
each with its own clientid4. each with its own clientid4.
An analysis of these symptoms leads to the conclusion that existing An analysis of these symptoms leads to the conclusion that existing
specifications have erred. They assume that locking state, including specifications have erred. They assume that locking state, including
both state ids and clientid4's, should be transferred as part of both state ids and clientid4's, should be transferred as part of
transparent state migration. The troubling symptoms arise from the transparent state migration. The troubling symptoms arise from the
failure to describe how migrating state is to be integrated with failure to describe how migrating state is to be integrated with
existing client definition structures on the destination server. existing client definition structures on the destination server.
Specification of requirements for the server to appropriately merge The need for the server to appropriately merge stateids associated
stateids associated with a common client boot instance encounters a with a common client boot instance encounters a difficult problem.
difficult problem. The issue is that the common client practice with The issue is that the common client practice with regard to the
regard to the presentation of unique strings specifying client presentation of unique strings specifying client identity makes it
identity makes it essentially impossible for the client to determine essentially impossible for the client to determine whether or not two
whether or not two stateids, originally generated on different stateids, originally generated on different servers are referable to
servers are referable to the same client. This practice is allowed the same client. This practice is allowed and endorsed by the
and endorsed, although not "RECOMMENDED", by the existing NFSv4.0 existing NFSv4.0 specification ([RFC7530]).
specification ([RFC7530]).
To further complicate matters, upon prototyping of clients However, upon prototyping of clients implementing an alternative
implementing an alternative approach, it has been found that there approach, it has been found that there exist servers which do not
exist servers which do not work well with these new clients. It work well with these new clients. It appears that current
appears that current circumstances, in which a particular client circumstances, in which a particular client implementation pattern
implementation pattern had been adopted universally, has resulted in had been adopted universally, has resulted in some servers not being
servers not being able to interoperate against alternate client able to interoperate against alternate client implementation
implementation patterns. As a result, we have a situation which patterns. As a result, we have a situation which requires careful
requires careful attention to compatibility issues to untangle. attention to compatibility issues to untangle.
This document updates the existing NFSv4.0 specification ([RFC7530]) This document updates the existing NFSv4.0 specification ([RFC7530])
as follows: as follows:
o It makes clear that NFSv4.0 supports multiple approaches to the o It makes clear that NFSv4.0 supports multiple approaches to the
construction of client id strings, including that formerly construction of client id strings, including that formerly
endorsed by existing NFSV4.0 specifications, and currently widely endorsed by existing NFSV4.0 specifications, and currently widely
deployed. deployed.
o It explains how clients can effectively use client id strings that
are presented to multiple servers.
o It addresses the potential compatibility issues that might arise o It addresses the potential compatibility issues that might arise
for clients adopting a previously non-favored client id for clients adopting a previously non-favored client id string
construction approach including the existence of servers which construction approach including the existence of servers which
have problems with the new approach. have problems with the new approach.
o It gives some guidance regarding the factors that might govern o It gives some guidance regarding the factors that might govern
clients' choice of a client id construction approach and clients' choice of a client id string construction approach and
RECOMMENDS that clients construct client id strings in manner that recommends that clients construct client id strings in manner that
supports lease merger if they intend to support transparent state supports lease merger if they intend to support transparent state
migration. migration.
o It specifies how state is to be transparently migrated, including o It specifies how state is to be transparently migrated, including
defining how state that arrives at a new server as part of defining how state that arrives at a new server as part of
migration is to be merged into existing leases for clients migration is to be merged into existing leases for clients
connected to the target server. connected to the target server.
o It makes further clarifications and corrections to address cases o It makes further clarifications and corrections to address cases
where the specification text does not take proper account of the where the specification text does not take proper account of the
issues raised by state migration or where it has been found that issues raised by state migration or where it has been found that
the existing text is insufficiently clear. the existing text is insufficiently clear. This includes a
revised definition of the SETCLIENTID operation in Section 8.4
which replaces Section 16.33 in [RFC7530]
For a more complete explanation of the choices made in addressing For a more complete explanation of the choices made in addressing
these issues, see [info-migr]). these issues, see [info-migr]).
4. Client Identity Definition 5. Client Identity Definition
This chapter is a replacement for sections 9.1.1 and 9.1.2 in This chapter is a replacement for sections 9.1.1 and 9.1.2 in
[RFC7530]. The replaced sections are named "client ID" and "Server [RFC7530]. The replaced sections are named "Client ID" and "Server
Release of Clientid." Release of Client ID".
It supersedes the replaced sections. It supersedes the replaced sections.
4.1. Differences from Replaced Sections 5.1. Differences from Replaced Sections
Because of the need for greater attention to and careful description Because of the need for greater attention to and careful description
of this area, this chapter is much larger than the sections it of this area, this chapter is much larger than the sections it
replaces. The principal changes/additions made by this chapter are: replaces. The principal changes/additions made by this chapter are:
o It corrects inconsistencies regarding the possible role or non- o It corrects inconsistencies regarding the possible role or non-
role of client IP address in construction of client id strings. role of the client IP address in construction of client id
strings.
o It clearly addresses the need to save client id strings or any o It clearly addresses the need to maintain a non-volatile record
changeable values that are used in their construction. across reboots of client id strings or any changeable values that
are used in their construction.
o It provides a more complete description of circumstances leading o It provides a more complete description of circumstances leading
to clientid4 invalidity and the appropriate recovery actions. to clientid4 invalidity and the appropriate recovery actions.
o It presents, as valid alternatives, two approaches to client id o It presents, as valid alternatives, two approaches to client id
string construction (named "uniform" and "non-uniform") and gives string construction (named "uniform" and "non-uniform") and gives
some implementation guidance to help implementers choose one or some implementation guidance to help implementers choose one or
the other of these. the other of these.
o It adds a discussion of issues involved for clients in interacting o It adds a discussion of issues involved for clients in interacting
with servers whose behavior is not consistent with use of uniform with servers whose behavior is not consistent with use of uniform
client id strings client id strings
o It adds a description of how server behavior might be used by the o It adds a description of how server behavior might be used by the
client to determine server address trunking patterns. client to determine when multiple server IP addresses correspond
to the same server.
4.2. Client Identity Data Items 5.2. Client Identity Data Items
The NFSv4 protocol contains a number of protocol entities to identify The NFSv4 protocol contains a number of protocol entities to identify
clients and client-based entities, for locking-related purposes: clients and client-based entities, for locking-related purposes:
o The nfs_client_id4 structure which uniquely identifies a specific o The nfs_client_id4 structure which uniquely identifies a specific
client boot instance. That identification is presented to the client boot instance. That identification is presented to the
server by doing a SETCLIENTID operation. server by doing a SETCLIENTID operation. The SETCLIENTID
operation is described in Section 8.4 which modifies a description
in Section 16.33 of [RFC7530]
o The clientid4 which is returned by the server upon completion of a o The clientid4 which is returned by the server upon completion of a
successful SETCLIENTID operation. This id is used by the client successful SETCLIENTID operation. This id is used by the client
to identify itself when doing subsequent locking-related to identify itself when doing subsequent locking-related
operations. A clientid4 is associated with a particular lease operations. A clientid4 is associated with a particular lease
whereby a client instance holds state on a server instance and may whereby a client instance holds state on a server instance and may
become invalid due to client reboot, server reboot, or other become invalid due to client reboot, server reboot, or other
circumstances. circumstances.
o Opaque arrays which are used together with the clientid4 to o Opaque arrays which are used together with the clientid4 to
designate within-client entities (e.g. processes) as the owners of designate within-client entities (e.g., processes) as the owners
opens (open-owners) and owners of byte-range locks (lock-owners). of opens (open-owners) and owners of byte-range locks (lock-
owners).
5.2.1. Client Identity Structure
The basis of the client identification infrastructure is encapsulated The basis of the client identification infrastructure is encapsulated
in the following data structure: in the following data structure, which also appears in Section 9.1.1
of [RFC7530]:
struct nfs_client_id4 { struct nfs_client_id4 {
verifier4 verifier; verifier4 verifier;
opaque id<NFS4_OPAQUE_LIMIT>; opaque id<NFS4_OPAQUE_LIMIT>;
}; };
The nfs_client_id4 structure uniquely defines a client boot instance The nfs_client_id4 structure uniquely defines a particular client
as follows: boot instance as follows:
o The id field is a variable-length string which uniquely identifies o The id field is a variable-length string which uniquely identifies
a specific client. Although, we describe it as a string and it is a specific client. Although, it is described here as a string and
often referred to as a "client string," it should be understood it is often referred to as a "client string," it should be
that the protocol defines this as opaque data. In particular, understood that the protocol defines this as opaque data. In
those receiving such an id should not assume that it will be in particular, those receiving such an id should not assume that it
the UTF-8 encoding. Servers MUST NOT reject an nfs_client_id4 will be in the UTF-8 encoding. Servers MUST NOT reject an
simply because the id string does not follow the rules of UTF-8 nfs_client_id4 simply because the id string does not follow the
encoding. rules of UTF-8 encoding.
The string MAY be different for each server network address that The encoding and decoding processes for this field (e.g., use of
the client accesses, rather than common to all server network network byte order) need to result in the same internal
addresses. representation whatever the endianness of the originating and
receiving machines.
o The verifier is a client incarnation identifier that is used by o The verifier field contains a client boot instance identifier that
the server to detect client reboots. Only if the verifier is is used by the server to detect client reboots. Only if the boot
different from that which the server has previously recorded in instance is different from that which the server has previously
connection with the client (as identified by the id field) does recorded in connection with the client (as identified by the id
the server cancel the client's leased state, once it receives field) does the server cancel the client's leased state. This
confirmation of the new nfs_clientd4 via SETCLIENTID_CONFIRM. cancellation occurs once it receives confirmation of the new
nfs_clientd4 via SETCLIENTID_CONFIRM. The SETCLIENTID_CONFIRM
operation is described in Section 16.34 of [RFC7530].
As a security measure, the server MUST NOT cancel a client's In order to prevent the possibility of malicious destruction of
leased state if the principal that established the state for a the locking state associated with a client, the server MUST NOT
given id string is not the same as the principal issuing the cancel a client's leased state if the principal that established
SETCLIENTID. the state for a given id string is not the same as the principal
issuing the SETCLIENTID.
There are several considerations for how the client generates the id There are several considerations for how the client generates the id
string: string:
o The string should be unique so that multiple clients do not o The string should be unique so that multiple clients do not
present the same string. The consequences of two clients present the same string. The consequences of two clients
presenting the same string range from one client getting an error presenting the same string range from one client getting an error
to one client having its leased state abruptly and unexpectedly to one client having its leased state abruptly and unexpectedly
canceled. canceled.
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this precludes the use of the implementation in an environment this precludes the use of the implementation in an environment
where there is no local disk and all file access is from an NFSv4 where there is no local disk and all file access is from an NFSv4
server. server.
o The string MAY be different for each server network address that o The string MAY be different for each server network address that
the client accesses, rather than common to all server network the client accesses, rather than common to all server network
addresses. addresses.
The considerations that might influence a client to use different The considerations that might influence a client to use different
strings for different network server addresses are explained in strings for different network server addresses are explained in
Section 4.4. Section 5.4.
o The algorithm for generating the string should not assume that the o The algorithm for generating the string should not assume that the
client's network address is forever fixed. Changes might occur clients' network addresses will remain the same for any set period
between client incarnations and even while the client is still of time. Changes might occur between client incarnations and even
running in its current incarnation. while the client is still running in its current incarnation.
Having the client id string change simply because of a network Changes to the client id string due to network address changes
address change would mean that successive SETCLIENTID operations would result in successive SETCLIENTID operations for the same
for the same client would appear as from different clients, client appearing as from different clients, interfering with the
interfering with the use of the nfs_client_id4 verifier to cancel use of the nfs_client_id4 verifier field to cancel state
state associated with previous boot instances of the same client. associated with previous boot instances of the same client.
The difficulty is more severe if the client address is the only The difficulty is more severe if the client address is the only
client-based information in the client id string. In such a case, client-based information in the client id string. In such a case,
there is a real risk that, after the client gives up the network there is a real risk that, after the client gives up the network
address, another client, using a similar algorithm for generating address, another client, using the same algorithm, would generate
the id string, will generate a conflicting id string. a conflicting id string. This would be likely to cause an
inappropriate loss of locking state. See Section 5.9 for detailed
guidance regarding client id string construction.
5.2.2. Client Identity Shorthand
Once a SETCLIENTID and SETCLIENTID_CONFIRM sequence has successfully Once a SETCLIENTID and SETCLIENTID_CONFIRM sequence has successfully
completed, the client uses the shorthand client identifier, of type completed, the client uses the shorthand client identifier, of type
clientid4, instead of the longer and less compact nfs_client_id4 clientid4, instead of the longer and less compact nfs_client_id4
structure. This shorthand client identifier (a client ID) is structure. This shorthand client identifier (a client ID) is
assigned by the server and should be chosen so that it will not assigned by the server and should be chosen so that it will not
conflict with a client ID previously assigned by same server. This conflict with a client ID previously assigned by same server, and, to
applies across server restarts or reboots. the degree practicable, by other servers as well. This applies
across server restarts or reboots.
Establishment of Client ID by a new incarnation of the client also
has the effect of immediately breaking any leased state that a
previous incarnation of the client might have had on the server, as
opposed to forcing the new client incarnation to wait for the leases
to expire. Breaking the lease state amounts to the server removing
all lock, share reservation, and, all delegation state not requested
using the CLAIM_DELEGATE_PREV claim type, associated with a client
having the same identity. For a discussion of delegation state
recovery, see Section 10.2.1 of [RFC7530].
Note that the SETCLIENTID and SETCLIENTID_CONFIRM operations have a Note that the SETCLIENTID and SETCLIENTID_CONFIRM operations have a
secondary purpose of establishing the information the server needs to secondary purpose of establishing the information the server needs to
make callbacks to the client for the purpose of supporting make callbacks to the client for the purpose of supporting
delegations. The client is able to change this information via delegations. The client is able to change this information via
SETCLIENTID and SETCLIENTID_CONFIRM within the same incarnation of SETCLIENTID and SETCLIENTID_CONFIRM within the same incarnation of
the client without causing removal of the client's leased state. the client without causing removal of the client's leased state.
Distinct servers MAY assign clientid4's independently, and will Distinct servers MAY assign clientid4's independently, and will
generally do so. Therefore, a client has to be prepared to deal with generally do so. Therefore, a client has to be prepared to deal with
multiple instances of the same clientid4 value received on distinct multiple instances of the same clientid4 value received on distinct
IP addresses, denoting separate entities. When trunking of server IP IP addresses, denoting separate entities. When trunking of server IP
addresses is not a consideration, a client should keep track of (IP- addresses is not a consideration, a client should keep track of (IP-
address, clientid4) pairs, so that each pair is distinct. For a address, clientid4) pairs, so that each pair is distinct. For a
discussion of how to address the issue in the face of possible discussion of how to address the issue in the face of possible
trunking of server IP addresses, see Section 4.4. trunking of server IP addresses, see Section 5.4.
Owners of opens and owners of byte-range locks are separate entities Owners of opens and owners of byte-range locks are separate entities
and remain separate even if the same opaque arrays are used to and remain separate even if the same opaque arrays are used to
designate owners of each. The protocol distinguishes between open- designate owners of each. The protocol distinguishes between open-
owners (represented by open_owner4 structures) and lock-owners owners (represented by open_owner4 structures) and lock-owners
(represented by lock_owner4 structures). (represented by lock_owner4 structures).
Both sorts of owners consist of a clientid4 and an opaque owner Both sorts of owners consist of a clientid4 and an opaque owner
string. For each client, the set of distinct owner values used with string. For each client, the set of distinct owner values used with
that client constitutes the set of owners of that type, for the given that client constitutes the set of owners of that type, for the given
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Each open is associated with a specific open-owner while each byte- Each open is associated with a specific open-owner while each byte-
range lock is associated with a lock-owner and an open-owner, the range lock is associated with a lock-owner and an open-owner, the
latter being the open-owner associated with the open file under which latter being the open-owner associated with the open file under which
the LOCK operation was done. the LOCK operation was done.
When a clientid4 is presented to a server and that clientid4 is not When a clientid4 is presented to a server and that clientid4 is not
valid, the server will reject the request with the an error that valid, the server will reject the request with the an error that
depends on the reason for clientid4 invalidity. The error depends on the reason for clientid4 invalidity. The error
NFS4ERR_ADMIN_REVOKED is returned when the invalidation is the result NFS4ERR_ADMIN_REVOKED is returned when the invalidation is the result
of administrative action, When the clientid4 is unrecognizable, the of administrative action. When the clientid4 is unrecognizable, the
error NFS4ERR_STALE_CLIENTID or NFS4ERR_EXPIRED may be returned. An error NFS4ERR_STALE_CLIENTID or NFS4ERR_EXPIRED may be returned. An
unrecognizable clientid4 can occur for a number of reasons: unrecognizable clientid4 can occur for a number of reasons:
o A server reboot causing loss of the server's knowledge of the o A server reboot causing loss of the server's knowledge of the
client. (Always returns NFS4ERR_STALE_CLIENTID) client. (Always returns NFS4ERR_STALE_CLIENTID)
o Client error sending an incorrect clientid4 or a valid clientid4 o Client error sending an incorrect clientid4 or a valid clientid4
to the wrong server. (May return either error). to the wrong server. (May return either error).
o Loss of lease state due to lease expiration. (Always returns o Loss of lease state due to lease expiration. (Always returns
NFS4ERR_EXPIRED) NFS4ERR_EXPIRED)
o Client or server error causing the server to believe that the o Client or server error causing the server to believe that the
client has rebooted (i.e. receiving a SETCLIENTID with an client has rebooted (i.e., receiving a SETCLIENTID with an
nfs_client_id4 which has a matching id string and a non-matching nfs_client_id4 which has a matching id string and a non-matching
boot verifier). (May return either error). boot instance id as the verifier). (May return either error).
o Migration of all state under the associated lease causes its non- o Migration of all state under the associated lease causes its non-
existence to be recognized on the source server. (Always returns existence to be recognized on the source server. (Always returns
NFS4ERR_STALE_CLIENTID) NFS4ERR_STALE_CLIENTID)
o Merger of state under the associated lease with another lease o Merger of state under the associated lease with another lease
under a different clientid causes the clientid4 serving as the under a different client ID causes the clientid4 serving as the
source of the merge to cease being recognized on its server. source of the merge to cease being recognized on its server.
(Always returns NFS4ERR_STALE_CLIENTID) (Always returns NFS4ERR_STALE_CLIENTID)
In the event of a server reboot, loss of lease state due to lease In the event of a server reboot, loss of lease state due to lease
expiration, or administrative revocation of a clientid4, the client expiration, or administrative revocation of a clientid4, the client
must obtain a new clientid4 by use of the SETCLIENTID operation and must obtain a new clientid4 by use of the SETCLIENTID operation and
then proceed to any other necessary recovery for the server reboot then proceed to any other necessary recovery for the server reboot
case (See the section entitled "Server Failure and Recovery"). In case (See Section 9.6.2 in [RFC7530]). In cases of server or client
cases of server or client error resulting in this error, use of error resulting in a clientid4 becoming unusable, use of SETCLIENTID
SETCLIENTID to establish a new lease is desirable as well. to establish a new lease is desirable as well.
In the last two cases, different recovery procedures are required. In cases in which loss of server knowledge of a clientid4 is the
See Section 5.1.1 for details. Note that in cases in which there is result of migration, different recovery procedures are required. See
any uncertainty about which sort of handling is applicable, the Section 6.1.1 for details. Note that in cases in which there is any
uncertainty about which sort of handling is applicable, the
distinguishing characteristic is that in reboot-like cases, the distinguishing characteristic is that in reboot-like cases, the
clientid4 and all associated stateids cease to exist while in clientid4 and all associated stateids cease to exist while in
migration-related cases, the clientid4 ceases to exist while the migration-related cases, the clientid4 ceases to exist while the
stateids are still valid. stateids are still valid.
The client must also employ the SETCLIENTID operation when it The client must also employ the SETCLIENTID operation when it
receives a NFS4ERR_STALE_STATEID error using a stateid derived from receives a NFS4ERR_STALE_STATEID error using a stateid derived from
its current clientid4, since this indicates a situation, such as its current clientid4, since this indicates a situation, such as
server reboot which has invalidated the existing clientid4 and server reboot which has invalidated the existing clientid4 and
associated stateids (see the section entitled "lock-owner" for associated stateids (see Section 9.1.5 in [RFC7530] for details).
details).
See the detailed descriptions of SETCLIENTID and SETCLIENTID_CONFIRM See the detailed descriptions of SETCLIENTID (in Section 8.4) and
for a complete specification of these operations. SETCLIENTID_CONFIRM (in Section 16.34 of [RFC7530]) for a complete
specification of these operations.
4.3. Server Release of Client ID 5.3. Server Release of Client ID
If the server determines that the client holds no associated state If the server determines that the client holds no associated state
for its clientid4, the server may choose to release that clientid4. for its clientid4, the server may choose to release that clientid4.
The server may make this choice for an inactive client so that The server may make this choice for an inactive client so that
resources are not consumed by those intermittently active clients. resources are not consumed by those intermittently active clients.
If the client contacts the server after this release, the server must If the client contacts the server after this release, the server must
ensure the client receives the appropriate error so that it will use ensure the client receives the appropriate error so that it will use
the SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish a new the SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish a new
identity. It should be clear that the server must be very hesitant identity. It should be clear that the server must be very hesitant
to release a client ID since the resulting work on the client to to release a client ID since the resulting work on the client to
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for each successive use of SETCLIENTID, then, barring an active for each successive use of SETCLIENTID, then, barring an active
denial of service attack, NFS4ERR_CLID_INUSE should never be denial of service attack, NFS4ERR_CLID_INUSE should never be
returned. returned.
However, client bugs, server bugs, or perhaps a deliberate change of However, client bugs, server bugs, or perhaps a deliberate change of
the principal owner of the id string (such as may occur in the case the principal owner of the id string (such as may occur in the case
in which a client changes security flavors, and under the new flavor, in which a client changes security flavors, and under the new flavor,
there is no mapping to the previous owner) will in rare cases result there is no mapping to the previous owner) will in rare cases result
in NFS4ERR_CLID_INUSE. in NFS4ERR_CLID_INUSE.
In that event, when the server gets a SETCLIENTID specifying a client In situations in which there is an apparent change of principal, when
id string for which the server has a clientid4 that currently has no the server gets a SETCLIENTID specifying a client id string for which
state, or for which it has state, but where the lease has expired, the server has a clientid4 that currently has no state, or for which
the server MUST allow the SETCLIENTID, rather than returning it has state, but where the lease has expired, the server MUST allow
NFS4ERR_CLID_INUSE. The server MUST then confirm the new client ID the SETCLIENTID, rather than returning NFS4ERR_CLID_INUSE. The
if followed by the appropriate SETCLIENTID_CONFIRM. server MUST then confirm the new client ID if followed by the
appropriate SETCLIENTID_CONFIRM.
4.4. Client Id String Approaches 5.4. Client Id String Approaches
One particular aspect of the construction of the nfs_client_id4 One particular aspect of the construction of the nfs_client_id4
string has proved recurrently troublesome. The client has a choice string has proved recurrently troublesome. The client has a choice
of: of:
o Presenting the same id string to multiple server addresses. This o Presenting the same id string to multiple server addresses. This
is referred to as the "uniform client id string approach" and is is referred to as the "uniform client id string approach" and is
discussed in Section 4.6. discussed in Section 5.6.
o Presenting different id strings to multiple server addresses. o Presenting different id strings to multiple server addresses.
This is referred to as the "non-uniform client id string approach" This is referred to as the "non-uniform client id string approach"
and is discussed in Section 4.5. and is discussed in Section 5.5.
Note that implementation considerations, including compatibility with Note that implementation considerations, including compatibility with
existing servers, may make it desirable for a client to use both existing servers, may make it desirable for a client to use both
approaches, based on configuration information, such as mount approaches, based on configuration information, such as mount
options. This issue will be discussed in Section 4.7. options. This issue will be discussed in Section 5.7.
Construction of the client id string has arisen as a difficult issue Construction of the client id string has arisen as a difficult issue
because of the way in which the NFS protocols have evolved. because of the way in which the NFS protocols have evolved. It is
useful to consider two points in that evolution.
o NFSv3 as a stateless protocol had no need to identify the state o NFSv3 as a stateless protocol had no need to identify the state
shared by a particular client-server pair. (See [RFC1813]). Thus shared by a particular client-server pair. (See [RFC1813]). Thus
there was no occasion to consider the question of whether a set of there was no need to consider the question of whether a set of
requests come from the same client, or whether two server IP requests come from the same client, or whether two server IP
addresses are connected to the same server. As the environment addresses are connected to the same server. As the environment
was one in which the user supplied the target server IP address as was one in which the user supplied the target server IP address as
part of incorporating the remote filesystem in the client's file part of incorporating the remote file system in the client's file
name space, there was no occasion to take note of server trunking. name space, there was no occasion to take note of server trunking.
Within a stateless protocol, the situation was symmetrical. The Within a stateless protocol, the situation was symmetrical. The
client has no server identity information and the server has no client has no server identity information and the server has no
client identity information. client identity information.
o NFSv4.1 is a stateful protocol with full support for client and o NFSv4.1 is a stateful protocol with full support for client and
server identity determination (See [RFC5661]). This enables the server identity determination (See [RFC5661]). This enables the
server to be aware when two requests come from the same client server to be aware when two requests come from the same client
(they are on sessions sharing a clientid4) and the client to be (they are on sessions sharing a clientid4) and the client to be
aware when two server IP addresses are connected to the same aware when two server IP addresses are connected to the same
server (they return the same server name in responding to an server. Section 2.10.5.1 of [RFC5661] explains how the client is
EXCHANGE_ID). able to assure itself that the connections are to the same logical
server.
NFSv4.0 is unfortunately halfway between these two. The two client NFSv4.0 is unfortunately halfway between these two. It introduced
id string approaches have arisen in attempts to deal with the new requirements such as the need to identify specific clients and
client instances without addressing server identity issues. The two
client id string approaches have arisen in attempts to deal with the
changing requirements of the protocol as implementation has proceeded changing requirements of the protocol as implementation has proceeded
and features that were not very substantial in early implementations and features that were not very substantial in early implementations
of NFSv4.0, became more substantial as implementation proceeded. of NFSv4.0, became more substantial as implementation proceeded.
o In the absence of any implementation of the fs_locations-related o In the absence of any implementation of the fs_locations-related
features (replication, referral, and migration), the situation is features (replication, referral, and migration), the situation is
very similar to that of NFSv3, with the addition of state but with very similar to that of NFSv3 (see Section 8.1 and the subsections
no concern to provide accurate client and server identity within section 8.4 of [RFC7530] for discussion of these features.
In this case, locking state has been added but there is no need
for concern about provision of accurate client and server identity
determination. This is the situation that gave rise to the non- determination. This is the situation that gave rise to the non-
uniform client id string approach. uniform client id string approach.
o In the presence of replication and referrals, the client may have o In the presence of replication and referrals, the client may have
occasion to take advantage of knowledge of server trunking occasion to take advantage of knowledge of server trunking
information. Even more important, transparent state migration, by information. Even more important, transparent state migration, by
transferring state among servers, causes difficulties for the non- transferring state among servers, causes difficulties for the non-
uniform client id string approach, in that the two different uniform client id string approach, in that the two different
client id strings sent to different IP addresses may wind up on client id strings sent to different IP addresses may wind up being
the same IP address, adding confusion. processed by the same logical server, adding confusion.
o A further consideration is that client implementations typically o A further consideration is that client implementations typically
provide NFSv4.1 by augmenting their existing NFSv4.0 provide NFSv4.1 by augmenting their existing NFSv4.0
implementation, not by providing two separate implementations. implementation, not by providing two separate implementations.
Thus the more NFSv4.0 and NFSv4.1 can work alike, the less complex Thus the more NFSv4.0 and NFSv4.1 can work alike, the less complex
are clients. This is a key reason why those implementing NFSv4.0 are clients. This is a key reason why those implementing NFSv4.0
clients might prefer using the uniform client string model, even clients might prefer using the uniform client string model, even
if they have chosen not to provide fs_locations-related features if they have chosen not to provide fs_locations-related features
in their NFSv4.0 client. in their NFSv4.0 client.
Both approaches have to deal with the asymmetry in client and server Both approaches have to deal with the asymmetry in client and server
identity information between client and server. Each seeks to make identity information between client and server. Each seeks to make
the client's and the server's views match. In the process, each the client's and the server's views match. In the process, each
encounters some combination of inelegant protocol features and/or encounters some combination of inelegant protocol features and/or
implementation difficulties. The choice of which to use is up to the implementation difficulties. The choice of which to use is up to the
client implementer and the sections below try to give some useful client implementer and the sections below try to give some useful
guidance. guidance.
4.5. Non-Uniform Client Id String Approach 5.5. Non-Uniform Client Id String Approach
The non-uniform client id string approach is an attempt to handle The non-uniform client id string approach is an attempt to handle
these matters in NFSv4.0 client implementations in as NFSv3-like a these matters in NFSv4.0 client implementations in as NFSv3-like a
way as possible. way as possible.
For a client using the non-uniform approach, all internal recording For a client using the non-uniform approach, all internal recording
of clientid4 values is to include, whether explicitly or implicitly, of clientid4 values is to include, whether explicitly or implicitly,
the server IP address so that one always has an (IP-address, the server IP address so that one always has an (IP-address,
clientid4) pair. Two such pairs from different servers are always clientid4) pair. Two such pairs from different servers are always
distinct even when the clientid4 values are the same, as they may distinct even when the clientid4 values are the same, as they may
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Making the client id string different on different server IP Making the client id string different on different server IP
addresses results in a situation in which a server has no way of addresses results in a situation in which a server has no way of
tying together information from the same client, when the client tying together information from the same client, when the client
accesses multiple server IP addresses. As a result, it will treat a accesses multiple server IP addresses. As a result, it will treat a
single client as multiple clients with separate leases for each single client as multiple clients with separate leases for each
server network address. Since there is no way in the protocol for server network address. Since there is no way in the protocol for
the client to determine if two network addresses are connected to the the client to determine if two network addresses are connected to the
same server, the resulting lack of knowledge is symmetrical and can same server, the resulting lack of knowledge is symmetrical and can
result in simpler client implementations in which there is a single result in simpler client implementations in which there is a single
clientid/lease per server network addresses. clientid4/lease per server network address.
Support for migration, particularly with transparent state migration, Support for migration, particularly with transparent state migration,
is more complex in the case of non-uniform client id strings. For is more complex in the case of non-uniform client id strings. For
example, migration of a lease can result in multiple leases for the example, migration of a lease can result in multiple leases for the
same client accessing the same server addresses, vitiating many of same client accessing the same server addresses, vitiating many of
the advantages of this approach. Therefore, client implementations the advantages of this approach. Therefore, client implementations
that support migration with transparent state migration SHOULD NOT that support migration with transparent state migration are likely to
use the non-uniform client id string approach, except where it is experience difficulties using the non-uniform client id string
necessary for compatibility with existing server implementations (For approach, and should not do so, except where it is necessary for
details of arranging use of multiple client id string approaches, see compatibility with existing server implementations (For details of
Section 4.7). arranging use of multiple client id string approaches, see
Section 5.7).
4.6. Uniform Client Id String Approach 5.6. Uniform Client Id String Approach
When the client id string is kept uniform, the server has the basis When the client id string is kept uniform, the server has the basis
to have a single clientid4/lease for each distinct client. The to have a single clientid4/lease for each distinct client. The
problem that has to be addressed is the lack of explicit server problem that has to be addressed is the lack of explicit server
identity information, which was made available in NFSv4.1. identity information, which was made available in NFSv4.1.
When the same client id string is given to multiple IP addresses, the When the same client id string is given to multiple IP addresses, the
client can determine whether two IP addresses correspond to a single client can determine whether two IP addresses correspond to a single
server, based on the server's behavior. This is the inverse of the server, based on the server's behavior. This is the inverse of the
strategy adopted for the non-uniform approach in which different strategy adopted for the non-uniform approach in which different
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server uses this information, two IP addresses on the same server server uses this information, two IP addresses on the same server
will behave as if they are talking to the same client, and this will behave as if they are talking to the same client, and this
difference in behavior allows the client to infer the server IP difference in behavior allows the client to infer the server IP
address trunking configuration, even though NFSv4.0 does not address trunking configuration, even though NFSv4.0 does not
explicitly provide this information. explicitly provide this information.
The approach given in the section below shows one example of how The approach given in the section below shows one example of how
this might be done. this might be done.
The uniform client id string approach makes it necessary to exercise The uniform client id string approach makes it necessary to exercise
more care in the definition of the nfs_client_id4 boot verifier: more care in the definition of the boot instance id sent as the
verifier field in an nfs_client_id4:
o In [RFC7530], the client is told to change the boot verifier when o In [RFC7530], the client is told to change the verifier field
reboot occurs, but there is no explicit statement as to the value when reboot occurs, but there is no explicit statement as to
converse, so that any requirement to keep the verifier constant the converse, so that any requirement to keep the verifier field
unless rebooting is only present by implication. constant unless rebooting is only present by implication.
o Many existing clients change the boot verifier every time they o Many existing clients change the boot instance id every time they
destroy and recreate the data structure that tracks an <IP- destroy and recreate the data structure that tracks an <IP-
address, clientid4> pair. This might happen if the last mount of address, clientid4> pair. This might happen if the last mount of
a particular server is removed, and then a fresh mount is created. a particular server is removed, and then a fresh mount is created.
Also, note that this might result in each <IP-address, clientid4> Also, note that this might result in each <IP-address, clientid4>
pair having its own boot verifier that is independent of the pair having its own boot instance id that is independent of the
others. others.
o Within the uniform client id string approach, an nfs_client_id4 o Within the uniform client id string approach, an nfs_client_id4
designates a globally known client instance, so that the boot designates a globally known client instance, so that the verifier
verifier should change if and only if a new client instance is field should change if and only if a new client instance is
created, typically as a result of a reboot. created, typically as a result of a reboot.
Clients using the uniform client id string approach are therefore Clients using the uniform client id string approach are therefore
well advised to use a verifier established only once for each well advised to use a verifier established only once for each
reboot, typically the reboot time. reboot, typically at reboot time.
The following are advantages for the implementation of using the The following are advantages for the implementation of using the
uniform client id string approach: uniform client id string approach:
o Clients can take advantage of server trunking (and clustering with o Clients can take advantage of server trunking (and clustering with
single-server-equivalent semantics) to increase bandwidth or single-server-equivalent semantics) to increase bandwidth or
reliability. reliability.
o There are advantages in state management so that, for example, we o There are advantages in state management so that, for example, one
never have a delegation under one clientid revoked because of a never has a delegation under one clientid4 revoked because of a
reference to the same file from the same client under a different reference to the same file from the same client under a different
clientid. clientid4.
o The uniform client id string approach allows the server to do any o The uniform client id string approach allows the server to do any
necessary automatic lease merger in connection with transparent necessary automatic lease merger in connection with transparent
state migration, without requiring any client involvement. This state migration, without requiring any client involvement. This
consideration is of sufficient weight to cause us to RECOMMEND use consideration is of sufficient weight to cause us to recommend use
of the uniform client id string approach for clients supporting of the uniform client id string approach for clients supporting
transparent state migration. transparent state migration.
The following implementation considerations might cause issues for The following implementation considerations might cause issues for
client implementations. client implementations.
o This approach is considerably different from the non-uniform o This approach is considerably different from the non-uniform
approach, which most client implementations have been following. approach, which most client implementations have been following.
Until substantial implementation experience is obtained with this Until substantial implementation experience is obtained with this
approach, reluctance to embrace something so new is to be approach, reluctance to embrace something so new is to be
expected. expected.
o Mapping between server network addresses and leases is more o Mapping between server network addresses and leases is more
complicated in that it is no longer a one-to-one mapping. complicated in that it is no longer a one-to-one mapping.
Another set of relevant considerations relate to privacy concerns,
which users of the client might have in that use of the uniform
client id string approach would enable multiple servers acting in
concert to determine when multiple requests received at different
times, derive from the same NFSv4 client. For example, this might
enable determination that multiple distinct user identities, in fact
are likely to correspond to requests made by the same person, even
when those request are directed to different servers.
How to balance these considerations depends on implementation goals. How to balance these considerations depends on implementation goals.
4.7. Mixing Client Id String Approaches 5.7. Mixing Client Id String Approaches
As noted above, a client which needs to use the uniform client id As noted above, a client which needs to use the uniform client id
string approach (e.g. to support migration), may also need to support string approach (e.g., to support migration), may also need to
existing servers with implementations that do not work properly in support existing servers with implementations that do not work
this case. properly in this case.
Some examples of such server issues include: Some examples of such server issues include:
o Some existing NFSv4.0 server implementations of IP address o Some existing NFSv4.0 server implementations of IP address
failover depend on clients' use of a non-uniform client id string failover depend on clients' use of a non-uniform client id string
approach. In particular, when a server supports both its own IP approach. In particular, when a server supports both its own IP
address and one failed over from a partner server, it may have address and one failed over from a partner server, it may have
separate sets of state applicable to the two IP addresses, owned separate sets of state applicable to the two IP addresses, owned
by different servers but residing on a single one. by different servers but residing on a single one.
In this situation, some servers have relied on clients' use of the In this situation, some servers have relied on clients' use of the
non-uniform client id string approach, as suggested but not non-uniform client id string approach, as suggested but not
mandated by [RFC7530], to keep these sets of state separate, and mandated by [RFC7530], to keep these sets of state separate, and
will have problems in handling clients using the uniform client id will have problems in handling clients using the uniform client id
string approach, in that such clients will see changes in trunking string approach, in that such clients will see changes in trunking
relationships whenever server failover and giveback occur. relationships whenever server failover and giveback occur.
o Some existing servers incorrectly return NFS4ERR_CLID_INUSE simply o Some existing servers incorrectly return NFS4ERR_CLID_INUSE simply
because there already exists a clientid for the same client, because there already exists a clientid4 for the same client,
established using a different IP address. This causes difficulty established using a different IP address. This causes difficulty
for a multi-homed client using the uniform client id string for a multi-homed client using the uniform client id string
approach. approach.
Although this behavior is not correct, such servers still exist Although this behavior is not correct, such servers still exist
and the spec should give clients guidance about dealing with the and this specification should give clients guidance about dealing
situation, as well as making the correct behavior clear. with the situation, as well as making the correct behavior clear.
In order to support use of these sorts of servers, the client can use In order to support use of these sorts of servers, the client can use
different client id string approaches for different mounts, as long different client id string approaches for different mounts, in order
as: to assure that,
o The uniform client id string approach is used when accessing o The uniform client id string approach is used when accessing
servers that may return NFS4ERR_MOVED and the client wishes to servers that may return NFS4ERR_MOVED and the client wishes to
enable transparent state migration." enable transparent state migration.
o The non-uniform client id string approach is used when accessing o The non-uniform client id string approach is used when accessing
servers whose implementations make them incompatible with the servers whose implementations make them incompatible with the
uniform client id string approach uniform client id string approach.
One effective way for clients to handle this is to support the Since the client cannot easily determine which of the above are true,
uniform client id string approach as the default, but allow a mount implementations are likely to rely on user-specified mount options to
option to specify use of the non-uniform client id string approach select the appropriate approach to use, in cases in which a client
for particular mount points, as long as such mount points are not supports simultaneous use of multiple approaches. Choice of a
used when migration is to be supported. default to use in such cases is up to the client implementation.
In the case in which the same server has multiple mounts, and both In the case in which the same server has multiple mounts, and both
approaches are specified for the same server, the client could have approaches are specified for the same server, the client could have
multiple clientid's corresponding to the same server, one for each multiple clientid4's corresponding to the same server, one for each
approach and would then have to keep these separate. approach and would then have to keep these separate.
4.8. Trunking Determination when Using Uniform Client Id Strings 5.8. Trunking Determination when Using Uniform Client Id Strings
This section provides an example of how trunking determination could This section provides an example of how trunking determination could
be done by a client following the uniform client id string approach be done by a client following the uniform client id string approach
(whether this is used for all mounts or not). Clients need not (whether this is used for all mounts or not). Clients need not
follow this procedure but implementers should make sure that the follow this procedure but implementers should make sure that the
issues dealt with by this procedure are all properly addressed. issues dealt with by this procedure are all properly addressed.
We need to clarify the various possible purposes of trunking It is best to clarify here the various possible purposes of trunking
determination and the corresponding requirements as to server determination and the corresponding requirements as to server
behavior. The following points should be noted: behavior. The following points should be noted:
o The primary purpose of the trunking determination algorithm is to o The primary purpose of the trunking determination algorithm is to
make sure that, if the server treats client requests on two IP make sure that, if the server treats client requests on two IP
addresses as part of the same client, the client will not be addresses as part of the same client, the client will not be
blind-sided and encounter disconcerting server behavior, as surprised and encounter disconcerting server behavior, as
mentioned in Section 4.6. Such behavior could occur if the client mentioned in Section 5.6. Such behavior could occur if the client
were unaware that all of its client requests for the two IP were unaware that all of its client requests for the two IP
addresses were being handled as part of a single client talking to addresses were being handled as part of a single client talking to
a single server. a single server.
o A second purpose is to be able to use knowledge of trunking o A second purpose is to be able to use knowledge of trunking
relationships for better performance, etc. relationships for better performance, etc.
o If a server were to give out distinct clientid's in response to o If a server were to give out distinct clientid4's in response to
receiving the same nfs_client_id4 on different network addresses, receiving the same nfs_client_id4 on different network addresses,
and acted as if these were separate clients, the primary purpose and acted as if these were separate clients, the primary purpose
of trunking determination would be met, as long as the server did of trunking determination would be met, as long as the server did
not treat them as part of the same client. In this case, the not treat them as part of the same client. In this case, the
server would be acting, with regard to that client, as if it were server would be acting, with regard to that client, as if it were
two distinct servers. This would interfere with the secondary two distinct servers. This would interfere with the secondary
purpose of trunking determination but there is nothing the client purpose of trunking determination but there is nothing the client
can do about that. can do about that.
o Suppose a server were to give such a client two different o Suppose a server were to give such a client two different
clientid's but act as if they were one. That is the only way that clientid4's but act as if they were one. That is the only way
the server could behave in a way that would defeat the primary that the server could behave in a way that would defeat the
purpose of the trunking determination algorithm. primary purpose of the trunking determination algorithm.
Servers MUST NOT do that. Servers MUST NOT behave that way.
For a client using the uniform approach, clientid4 values are treated For a client using the uniform approach, clientid4 values are treated
as important information in determining server trunking patterns. as important information in determining server trunking patterns.
For two different IP addresses to return the same clientid4 value is For two different IP addresses to return the same clientid4 value is
a necessary, though not a sufficient condition for them to be a necessary, though not a sufficient condition for them to be
considered as connected to the same server. As a result, when two considered as connected to the same server. As a result, when two
different IP addresses return the same clientid4, the client needs to different IP addresses return the same clientid4, the client needs to
determine, using the procedure given below or otherwise, whether the determine, using the procedure given below or otherwise, whether the
IP addresses are connected to the same server. For such clients, all IP addresses are connected to the same server. For such clients, all
internal recording of clientid4 values needs to include, whether internal recording of clientid4 values needs to include, whether
explicitly or implicitly, identification of the server from which the explicitly or implicitly, identification of the server from which the
clientid4 was received so that one always has a (server, clientid4) clientid4 was received so that one always has a (server, clientid4)
pair. Two such pairs from different servers are always considered pair. Two such pairs from different servers are always considered
distinct even when the clientid4 values are the same, as they may distinct even when the clientid4 values are the same, as they may
occasionally be. occasionally be.
In order to make this approach work, the client must have accessible, In order to make this approach work, the client must have certain
for each nfs_client_id4 used by the uniform approach (only one in information accessible for each nfs_client_id4 used by the uniform
general) a list of all server IP addresses, together with the approach (only one in general). The client needs to maintain a list
associated clientid4 values, SETCLIENTID principals and of all server IP addresses, together with the associated clientid4
authentication flavors. As a part of the associated data structures, values, SETCLIENTID principals and authentication flavors. As a part
there should be the ability to mark a server IP structure as having of the associated data structures, there should be the ability to
the same server as another and to mark an IP address as currently mark a server IP structure as having the same server as another and
unresolved. One way to do this is to a allow each such entry to to mark an IP address as currently unresolved. One way to do this is
point to another with the pointer value being one of: to a allow each such entry to point to another with the pointer value
being one of:
o A pointer to another entry for an IP address associated with the o A pointer to another entry for an IP address associated with the
same server, where that IP address is the first one referenced to same server, where that IP address is the first one referenced to
access that server. access that server.
o A pointer to the current entry if there is no earlier IP address o A pointer to the current entry if there is no earlier IP address
associated with the same server, i.e. where the current IP address associated with the same server, i.e., where the current IP
is the first one referenced to access that server. We'll refer to address is the first one referenced to access that server. The
such an IP address as the lead IP address for a given server. text below refers to such an IP address as the lead IP address for
a given server.
o The value NULL if the address's server identity is currently o The value NULL if the address's server identity is currently
unresolved. unresolved.
In order to keep the above information current, in the interests of In order to keep the above information current, in the interests of
the most effective trunking determination, RENEWs should be the most effective trunking determination, RENEWs should be
periodically done on each server. However, even if this is not done, periodically done on each server. However, even if this is not done,
the primary purpose of the trunking determination algorithm, to the primary purpose of the trunking determination algorithm, to
prevent confusion due to trunking hidden from the client, will be prevent confusion due to trunking hidden from the client, will be
achieved. achieved.
Given this apparatus, when a SETCLIENTID is done and a clientid4 Given this apparatus, when a SETCLIENTID is done and a clientid4
returned, the data structure can be searched for a matching clientid4 returned, the data structure can be searched for a matching clientid4
and if such is found, further processing can be done to determine and if such is found, further processing can be done to determine
whether the clientid4 match is accidental, or the result of trunking. whether the clientid4 match is accidental, or the result of trunking.
In this algorithm, when SETCLIENTID is done it will use the common In this algorithm, when SETCLIENTID is done initially, it will use
nfs_client_id4 and specify the current target IP address as part of the common nfs_client_id4 and specify the current target IP address
the callback parameters. We call the clientid4 and SETCLIENTID as callback.cb_location within the callback parameters. We call the
verifier returned by this operation XC and XV. clientid4 and SETCLIENTID verifier returned by this operation XC and
XV.
This choice of callback parameters is provisional and reflects the
client's preferences in the event that the IP address is not trunked
with other IP addresses. The algorithm is constructed so that only
the appropriate callback parameters, reflecting observed trunking
patterns is actually confirmed.
Note that when the client has done previous SETCLIENTID's, to any IP Note that when the client has done previous SETCLIENTID's, to any IP
addresses, with more than one principal or authentication flavor, we addresses, with more than one principal or authentication flavor, one
have the possibility of receiving NFS4ERR_CLID_INUSE, since we do not has the possibility of receiving NFS4ERR_CLID_INUSE, since it is not
yet know which of our connections with existing IP addresses might be yet knows which of the connections with existing IP addresses might
trunked with our current one. In the event that the SETCLIENTID be trunked with the current one. In the event that the SETCLIENTID
fails with NFS4ERR_CLID_INUSE, one must try all other combinations of fails with NFS4ERR_CLID_INUSE, one must try all other combinations of
principals and authentication flavors currently in use and eventually principals and authentication flavors currently in use and eventually
one will be correct and not return NFS4ERR_CLID_INUSE. one will be correct and not return NFS4ERR_CLID_INUSE.
Note that at this point, no SETCLIENTID_CONFIRM has yet been done. Note that at this point, no SETCLIENTID_CONFIRM has yet been done.
This is because our SETCLIENTID has either established a new This is because the SETCLIENTID just done has either established a
clientid4 on a previously unknown server or changed the callback new clientid4 on a previously unknown server or changed the callback
parameters on a clientid4 associated with some already known server. parameters on a clientid4 associated with some already known server.
Given that we don't want to confirm something that we are not sure we Given it is undesirable to confirm something that should not happen,
want to happen, what is to be done next depends on information about what is to be done next depends on information about existing
existing clientid4's. clientid4's.
o If no matching clientid4 is found, the IP address X and clientid4 o If no matching clientid4 is found, the IP address X and clientid4
XC are added to the list and considered as having no existing XC are added to the list and considered as having no existing
known IP addresses trunked with it. The IP address is marked as a known IP addresses trunked with it. The IP address is marked as a
lead IP address for a new server. A SETCLIENTID_CONFIRM is done lead IP address for a new server. A SETCLIENTID_CONFIRM is done
using XC and XV. using XC and XV.
o If a matching clientid4 is found which is marked unresolved, o If a matching clientid4 is found which is marked unresolved,
processing on the new IP address is suspended. In order to processing on the new IP address is suspended. In order to
simplify processing, there can only be one unresolved IP address simplify processing, there can only be one unresolved IP address
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used should be used for address X as well. This will avoid any used should be used for address X as well. This will avoid any
possibility that NFS4ERR_CLID_INUSE will be returned for the possibility that NFS4ERR_CLID_INUSE will be returned for the
SETCLIENTID and SETCLIENTID_CONFIRM to be done below, as long as SETCLIENTID and SETCLIENTID_CONFIRM to be done below, as long as
the server(s) at IP addresses IPn and X are correctly implemented. the server(s) at IP addresses IPn and X are correctly implemented.
o A SETCLIENTID is done to update the callback parameters to reflect o A SETCLIENTID is done to update the callback parameters to reflect
the possibility that X will be marked as associated with the the possibility that X will be marked as associated with the
server whose lead IP address is IPn. The specific callback server whose lead IP address is IPn. The specific callback
parameters chosen, in terms of cb_client4 and callback_ident, are parameters chosen, in terms of cb_client4 and callback_ident, are
up to the client and should reflect its preferences as to callback up to the client and should reflect its preferences as to callback
handling for the common clientid, in the event that X and IPn are handling for the common clientid4, in the event that X and IPn are
trunked together. When we do a SETCLIENTID on IP address IPn, we trunked together. When a SETCLIENTID is done on IP address IPn, a
get back a setclientid_confirm value (in the form of a verifier4), setclientid_confirm value (in the form of a verifier4) is
which we call SCn. returned, which will be referred to as SCn.
Note that the NFSv4.0 specification requires the server to make Note that the NFSv4.0 specification requires the server to make
sure that such verifiers are very unlikely to be regenerated. sure that such verifiers are very unlikely to be regenerated.
Given that it is already highly unlikely that the clientid XC is Given that it is already highly unlikely that the clientid4 XC is
duplicated by distinct servers, the probability that SCn is duplicated by distinct servers, the probability that SCn is
duplicated as well has to be considered vanishingly small. Note duplicated as well has to be considered vanishingly small. Note
also that the callback update procedure can be repeated multiple also that the callback update procedure can be repeated multiple
times to reduce the probability of spurious matches further. times to reduce the probability of spurious matches further.
o We save the setclientid_confirm value SCn for later use in o The setclientid_confirm value SCn is saved for later use in
confirming the SETCLIENTID done to IPn. confirming the SETCLIENTID done to IPn.
Once the SCn values are gathered up by the procedure above, they are Once the SCn values are gathered up by the procedure above, they are
each tested by being used as the verifier for a SETCLIENTID_CONFIRM each tested by being used as the verifier for a SETCLIENTID_CONFIRM
operation directed to the original IP address X, whose trunking operation directed to the original IP address X, whose trunking
relationships are to be determined. These RPC operations may be done relationships are to be determined. These RPC operations may be done
in parallel. in parallel.
There are a number of things that should be noted at this point. There are a number of things that should be noted at this point.
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o When a SETCLIENTID_CONFIRM is rejected by a given IPn, the client o When a SETCLIENTID_CONFIRM is rejected by a given IPn, the client
should be aware of the possibility that the rejection is due to XC should be aware of the possibility that the rejection is due to XC
(rather than XV) being invalid. This situation can be addressed (rather than XV) being invalid. This situation can be addressed
by doing a RENEW specifying XC directed to the IP address X. If by doing a RENEW specifying XC directed to the IP address X. If
that operation succeeds, then the rejection is to be acted on that operation succeeds, then the rejection is to be acted on
normally since either XV is invalid on IPn or XC has become normally since either XV is invalid on IPn or XC has become
invalid on IPn while it is valid on X, showing that IPn and X are invalid on IPn while it is valid on X, showing that IPn and X are
not trunked. If, on the other hand, XC is not valid on X, then not trunked. If, on the other hand, XC is not valid on X, then
the trunking detection process should be restarted once a new the trunking detection process should be restarted once a new
clientid is established on X. client ID is established on X.
o In the event of a reboot detected on any server lead IP, the set o In the event of a reboot detected on any server lead IP, the set
of IP addresses associated with the server should not change and of IP addresses associated with the server should not change and
state should be re-established for the lease as a whole, using all state should be re-established for the lease as a whole, using all
available connected server IP addresses. It is prudent to verify available connected server IP addresses. It is prudent to verify
connectivity by doing a RENEW using the new clientid4 on each such connectivity by doing a RENEW using the new clientid4 on each such
server address before using it, however. server address before using it, however.
Another situation not discussed explicitly above is the possibility Another situation not discussed explicitly above is the possibility
that a SETCLIENTID done to one of the IPn addresses might take so that a SETCLIENTID done to one of the IPn addresses might take so
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o The client locking-related code could be made more tolerant of o The client locking-related code could be made more tolerant of
what would otherwise be considered anomalous results due to an what would otherwise be considered anomalous results due to an
unrecognized trunking relationship. The client could use the unrecognized trunking relationship. The client could use the
appearance of behavior explainable by a previously unknown appearance of behavior explainable by a previously unknown
trunking relationship as the cue to consider the addresses as trunking relationship as the cue to consider the addresses as
trunked. trunked.
This choice has a lot of complexity associated with it, and it is This choice has a lot of complexity associated with it, and it is
likely that few implementations will use it. When the set of likely that few implementations will use it. When the set of
locking state on IPn is small (e.g. a single stateid) but not locking state on IPn is small (e.g., a single stateid) but not
empty, most client implementations are likely to either fail the empty, most client implementations are likely to either fail the
MOUNT or implement a more stringent verification procedure using MOUNT or implement a more stringent verification procedure using
the existing stateid on IPn as a basis to generate further state the existing stateid on IPn as a basis to generate further state
as raw material for the trunking verification process. as raw material for the trunking verification process.
4.9. Client Id String Construction Details 5.9. Client Id String Construction Details
This section gives more detailed guidance on client id string
construction. The guidance in this section will cover cases in which
either the uniform or the non-uniform approach to the client id
string is used.
This section gives more detailed guidance on client id construction.
Note that among the items suggested for inclusion, there are many Note that among the items suggested for inclusion, there are many
that may conceivably change. In order for the client id string to that may conceivably change. In order for the client id string to
remain valid in such circumstances, the client should either: remain valid in such circumstances, the client SHOULD either:
o Use a saved copy of such value, rather than the changeable value o Use a saved copy of such value, rather than the changeable value
itself. itself.
o Save the constructed client id string, rather than constructing it o Save the constructed client id string, rather than constructing it
anew at SETCLIENTID time, based on unchangeable parameters and anew at SETCLIENTID time, based on unchangeable parameters and
saved copies of changeable data items. saved copies of changeable data items.
A file is not always a valid choice to store such information, given A file is not always a valid choice to store such information, given
the existence of diskless clients. In such situations, whatever the existence of diskless clients. In such situations, whatever
facilities exist for a client to store configuration information such facilities exist for a client to store configuration information such
as boot arguments should be used. as boot arguments should be used.
Given the considerations listed in Section 4.2, an example of a well Given the considerations listed in Section 5.2.1, an id string would
generated id string is one that includes: be one that includes as its basis:
o The client's network address, or more safely, an address that has o An identifier uniquely associated with the node on which the
previously been used in that capacity. client is running.
o For a user level NFSv4.0 client, it should contain additional o For a user level NFSv4.0 client, it should contain additional
information to distinguish the client from other user level information to distinguish the client from a kernel-based client
clients running on the same host, such as a universally unique and from other user-level clients running on the same node, such
identifier (UUID). as a universally unique identifier (UUID).
o Where the non-uniform approach is to be used, the IP address of
the server.
o Additional information that tends to be unique, such as one or o Additional information that tends to be unique, such as one or
more of: more of:
* The client machine's serial number (for privacy reasons, it is
best to perform some one way function on the serial number).
* A MAC address. Note that this can cause difficulties when
there are configuration changes or when a client has multiple
network adapters.
* The timestamp of when the NFSv4 software was first installed on * The timestamp of when the NFSv4 software was first installed on
the client (though this is subject to the previously mentioned the client (though this is subject to the previously mentioned
caution about using information that is stored in a file, caution about using information that is stored in a file,
because the file might only be accessible over NFSv4). because the file might only be accessible over NFSv4).
* A true random number, generally established once and saved. * A true random number, generally established once and saved.
5. Locking and Multi-Server Namespace With regard to the identifier associated with the node on which the
client is running, the following possibilities are likely candidates.
o The client machine's serial number.
o The client's IP address. Note that this SHOULD be treated as a
changeable value.
o A MAC address. Note that this also should be considered a
changeable value because of the possibility of configuration
changes.
Privacy concerns may be an issue if some of the items above (e.g.,
machine serial number, MAC address) are used. When it is necessary
to use such items to ensure uniqueness, application of a one-way hash
function is desirable. When the non-uniform approach is used, that
hash function should be applied to all of the components chosen as a
unit rather that to particular individual elements.
6. Locking and Multi-Server Namespace
This chapter contains a replacement for section 9.14, "Migration, This chapter contains a replacement for section 9.14, "Migration,
Replication, and State", in [RFC7530]. Replication, and State", in [RFC7530].
The replacement is in Section 5.1 and supersedes the replaced The replacement is in Section 6.1 and supersedes the replaced
section. section.
The changes made can be briefly summarized as follows: The changes made can be briefly summarized as follows:
o Adding text to address the case of stateid conflict on migration. o Adding text to address the case of stateid conflict on migration.
o Specifying that when leases are moved, as a result of filesystem o Specifying that when leases are moved, as a result of file system
migration, they are to be merged with leases on the destination migration, they are to be merged with leases on the destination
server that are connected to the same client. server that are connected to the same client.
o Adding text that deals with the case of a clientid4 being changed o Adding text that deals with the case of a clientid4 being changed
on state transfer as a result of conflict with an existing on state transfer as a result of conflict with an existing
clientid4. clientid4.
o Adding a section describing how information associated with o Adding a section describing how information associated with open-
openowners and lockowners is to be managed with regard to owners and lock-owners is to be managed with regard to migration.
migration.
o The description of handling of the NFS4ERR_LEASE_MOVED has been o The description of handling of the NFS4ERR_LEASE_MOVED has been
rewritten for greater clarity. rewritten for greater clarity.
5.1. Lock State and Filesystem Transitions 6.1. Lock State and File System Transitions
When responsibility for handling a given filesystem is transferred to File systems may transition to a different server in several
a new server (migration) or the client chooses to use an alternate circumstances:
server (e.g., in response to server unresponsiveness) in the context
of filesystem replication, the appropriate handling of state shared
between the client and server (i.e., locks, leases, stateids, and
client IDs) is as described below. The handling differs between
migration and replication.
If a server replica or a server immigrating a filesystem agrees to, o Responsibility for handling a given file system is transferred to
a new server via migration.
o A client may choose to use an alternate server (e.g., in response
to server unresponsiveness) in the context of file system
replication.
In such cases, the appropriate handling of state shared between the
client and server (i.e., locks, leases, stateids, and client IDs) is
as described below. The handling differs between migration and
replication.
If a server replica or a server immigrating a file system agrees to,
or is expected to, accept opaque values from the client that or is expected to, accept opaque values from the client that
originated from another server, then it is a wise implementation originated from another server, then it is a wise implementation
practice for the servers to encode the "opaque" values in network practice for the servers to encode the "opaque" values in network
byte order. When doing so, servers acting as replicas or immigrating byte order (i.e., in a big-endian format). When doing so, servers
filesystems will be able to parse values like stateids, directory acting as replicas or immigrating file systems will be able to parse
cookies, filehandles, etc. even if their native byte order is values like stateids, directory cookies, filehandles, etc. even if
different from that of other servers cooperating in the replication their native byte order is different from that of other servers
and migration of the filesystem. cooperating in the replication and migration of the file system.
5.1.1. Migration and State 6.1.1. Migration and State
In the case of migration, the servers involved in the migration of a In the case of migration, the servers involved in the migration of a
filesystem SHOULD transfer all server state associated with the file system should transfer all server state associated with the
migrating filesystem from source to the destination server. This migrating file system from source to the destination server. If
must be done in a way that is transparent to the client. This state state is transferred, this MUST be done in a way that is transparent
transfer will ease the client's transition when a filesystem to the client. This state transfer will ease the client's transition
migration occurs. If the servers are successful in transferring all when a file system migration occurs. If the servers are successful
state, the client will continue to use stateids assigned by the in transferring all state, the client will continue to use stateids
original server. Therefore the new server must recognize these assigned by the original server. Therefore the new server must
stateids as valid and treat them as representing the same locks as recognize these stateids as valid and treat them as representing the
they did on the source server. same locks as they did on the source server.
In this context, the phrase "the same locks" means: In this context, the phrase "the same locks" means:
o That they are associated with the same file o That they are associated with the same file
o That they represent the same types of locks, whether opens, o That they represent the same types of locks, whether opens,
delegations, advisory byte-range locks, or mandatory byte-range delegations, advisory byte-range locks, or mandatory byte-range
locks. locks.
o That they have the same lock particulars, including such things as o That they have the same lock particulars, including such things as
skipping to change at page 25, line 9 skipping to change at page 29, line 27
o That they are associated with the same owner string(s). o That they are associated with the same owner string(s).
If transferring stateids from server to server would result in a If transferring stateids from server to server would result in a
conflict for an existing stateid for the destination server with the conflict for an existing stateid for the destination server with the
existing client, transparent state migration MUST NOT happen for that existing client, transparent state migration MUST NOT happen for that
client. Servers participating in using transparent state migration client. Servers participating in using transparent state migration
should co-ordinate their stateid assignment policies to make this should co-ordinate their stateid assignment policies to make this
situation unlikely or impossible. The means by which this might be situation unlikely or impossible. The means by which this might be
done, like all of the inter-server interactions for migration, are done, like all of the inter-server interactions for migration, are
not specified by the NFS version 4.0 protocol. not specified by the NFS version 4.0 protocol (either in [RFC7530] or
this update).
A client may determine the disposition of migrated state by using a A client may determine the disposition of migrated state by using a
stateid associated with the migrated state on the new server. stateid associated with the migrated state on the new server.
o If the stateid is not valid and an error NFS4ERR_BAD_STATEID is o If the stateid is not valid and an error NFS4ERR_BAD_STATEID is
received, either transparent state migration has not occurred or received, either transparent state migration has not occurred or
the state was purged due to boot verifier mismatch. the state was purged due to a mismatch in the verifier (i.e., the
boot instance id).
o If the stateid is valid, transparent state migration has occurred. o If the stateid is valid, transparent state migration has occurred.
Since responsibility for an entire filesystem is transferred with a Since responsibility for an entire file system is transferred with a
migration event, there is no possibility that conflicts will arise on migration event, there is no possibility that conflicts will arise on
the destination server as a result of the transfer of locks. the destination server as a result of the transfer of locks.
The servers may choose not to transfer the state information upon The servers may choose not to transfer the state information upon
migration. However, this choice is discouraged, except where migration. However, this choice is discouraged, except where
specific issues such as stateid conflicts make it necessary. When a specific issues such as stateid conflicts make it necessary. When a
server implements migration and it does not transfer state server implements migration and it does not transfer state
information, it SHOULD provide a filesystem-specific grace period, to information, it MUST provide a file-system-specific grace period, to
allow clients to reclaim locks associated with files in the migrated allow clients to reclaim locks associated with files in the migrated
filesystem. If it did not do so, clients would have to re-obtain file system. If it did not do so, clients would have to re-obtain
locks, with no assurance that a conflicting lock was not granted locks, with no assurance that a conflicting lock was not granted
after the filesystem was migrated and before the lock was re- after the file system was migrated and before the lock was re-
obtained. obtained.
In the case of migration without state transfer, when the client In the case of migration without state transfer, when the client
presents state information from the original server (e.g. in a RENEW presents state information from the original server (e.g., in a RENEW
op or a READ op of zero length), the client must be prepared to op or a READ op of zero length), the client must be prepared to
receive either NFS4ERR_STALE_CLIENTID or NFS4ERR_BAD_STATEID from the receive either NFS4ERR_STALE_CLIENTID or NFS4ERR_BAD_STATEID from the
new server. The client should then recover its state information as new server. The client should then recover its state information as
it normally would in response to a server failure. The new server it normally would in response to a server failure. The new server
must take care to allow for the recovery of state information as it must take care to allow for the recovery of state information as it
would in the event of server restart. would in the event of server restart.
In those situations in which state has not been transferred, as shown In those situations in which state has not been transferred, as shown
by a return of NFS4ERR_BAD_STATEID, the client may attempt to reclaim by a return of NFS4ERR_BAD_STATEID, the client may attempt to reclaim
locks in order to take advantage of cases in which the destination locks in order to take advantage of cases in which the destination
server has set up a file-system-specific grace period in support of server has set up a file-system-specific grace period in support of
the migration. the migration.
5.1.1.1. Migration and Clientid's 6.1.1.1. Migration and Client IDs
Handling of clientid values is similar to that for stateids. Handling of clientid4 values is similar to that for stateids.
However, there are some differences that derive from the fact that a However, there are some differences that derive from the fact that a
clientid is an object which spans multiple filesystems while a clientid4 is an object which spans multiple file systems while a
stateid is inherently limited to a single filesystem. stateid is inherently limited to a single file system.
The clientid4 and nfs_client_id4 information (id string and boot The clientid4 and nfs_client_id4 information (id string and boot
verifier) will be transferred with the rest of the state information instance id) will be transferred with the rest of the state
and the destination server should use that information to determine information and the destination server should use that information to
appropriate clientid4 handling. Although the destination server may determine appropriate clientid4 handling. Although the destination
make state stored under an existing lease available under the server may make state stored under an existing lease available under
clientid4 used on the source server, the client should not assume the clientid4 used on the source server, the client should not assume
that this is always so. In particular, that this is always so. In particular,
o If there is an existing lease with an nfs_client_id4 that matches o If there is an existing lease with an nfs_client_id4 that matches
a migrated lease (same id string and boot verifier), the server a migrated lease (same id string and verifier), the server SHOULD
SHOULD merge the two, making the union of the sets of stateids merge the two, making the union of the sets of stateids available
available under the clientid4 for the existing lease. As part of under the clientid4 for the existing lease. As part of the lease
the lease merger, the expiration time of the lease will reflect merger, the expiration time of the lease will reflect renewal done
renewal done within either of the ancestor leases (and so will within either of the ancestor leases (and so will reflect the
reflect the latest of the renewals). latest of the renewals).
o If there is an existing lease with an nfs_client_id4 that o If there is an existing lease with an nfs_client_id4 that
partially matches a migrated lease (same id string and a different partially matches a migrated lease (same id string and a different
boot verifier), the server MUST eliminate one of the two, possibly (boot) verifier), the server MUST eliminate one of the two,
invalidating one of the ancestor clientid4's. Since boot possibly invalidating one of the ancestor clientid4's. Since boot
verifiers are not ordered, the later lease renewal time will instance id's are not ordered, the later lease renewal time will
prevail. prevail.
o If the destination server already has the transferred clientid4 in o If the destination server already has the transferred clientid4 in
use for another purpose, it is free to substitute a different use for another purpose, it is free to substitute a different
clientid4 and associate that with the transferred nfs_client_id4. clientid4 and associate that with the transferred nfs_client_id4.
When leases are not merged, the transfer of state should result in When leases are not merged, the transfer of state should result in
creation of a confirmed client record with empty callback information creation of a confirmed client record with empty callback information
but matching the {v, x, c} with v and x derived from the transferred but matching the {v, x, c} with v and x derived from the transferred
client information and c chosen by the destination server. client information and c chosen by the destination server. For a
description of this notation, see Section 8.4.5
In such cases, the client SHOULD re-establish new callback In such cases, the client SHOULD re-establish new callback
information with the new server as soon as possible, according to information with the new server as soon as possible, according to
sequences described in sections "Operation 35: SETCLIENTID - sequences described in sections "Operation 35: SETCLIENTID -
Negotiate Client ID" and "Operation 36: SETCLIENTID_CONFIRM - Confirm Negotiate Client ID" and "Operation 36: SETCLIENTID_CONFIRM - Confirm
Client ID". This ensures that server operations are not delayed due Client ID". This ensures that server operations are not delayed due
to an inability to recall delegations. The client can determine the to an inability to recall delegations. The client can determine the
new clientid (the value c) from the response to SETCLIENTID. new clientid4 (the value c) from the response to SETCLIENTID.
The client can use its own information about leases with the The client can use its own information about leases with the
destination server to see if lease merger should have happened. When destination server to see if lease merger should have happened. When
there is any ambiguity, the client MAY use the above procedure to set there is any ambiguity, the client MAY use the above procedure to set
the proper callback information and find out, as part of the process, the proper callback information and find out, as part of the process,
the correct value of its clientid with respect to the server in the correct value of its clientid4 with respect to the server in
question. question.
5.1.1.2. Migration and State Owner Information 6.1.1.2. Migration and State Owner Information
In addition to stateids, the locks they represent, and clientid In addition to stateids, the locks they represent, and client
information, servers also need to transfer information related to the identity information, servers also need to transfer information
current status of openowners and lockowners. related to the current status of open-owners and lock-owners.
This information includes: This information includes:
o The sequence number of the last operation associated with the o The sequence number of the last operation associated with the
particular owner. particular owner.
o Information regarding the results of the last operation, o Information regarding the results of the last operation,
sufficient to allow reissued operations to be correctly responded sufficient to allow reissued operations to be correctly responded
to. to.
When clients are implemented to isolate each openowner and lockowner When individual open-owners and lock-owners have only been used in
to a particular filesystem, the server SHOULD transfer this connection with a particular file system, the server SHOULD transfer
information together with the lock state. The owner ceases to exist this information together with the lock state. The owner ceases to
on the source server and is reconstituted on the destination server. exist on the source server and is reconstituted on the destination
server. This will happen in the case of clients which have been
written to isolate each owner to a specific filesystem, but may
happen for other clients as well.
Note that when servers take this approach for all owners whose state Note that when servers take this approach for all owners whose state
is limited to the particular filesystem being migrated, doing so will is limited to the particular file system being migrated, doing so
not cause difficulties for clients not adhering to an approach in will not cause difficulties for clients not adhering to an approach
which owners are isolated to particular filesystems. As long as the in which owners are isolated to particular file systems. As long as
client recognizes the loss of transferred state, the protocol allows the client recognizes the loss of transferred state, the protocol
the owner in question to disappear and the client may have to deal allows the owner in question to disappear and the client may have to
with an owner confirmation request that would not have occurred in deal with an owner confirmation request that would not have occurred
the absence of the migration. in the absence of the migration.
When migration occurs and the source server discovers an owner whose When migration occurs and the source server discovers an owner whose
state includes the migrated filesystem but other filesystems as well, state includes the migrated file system but other file systems as
it cannot transfer the associated owner state. Instead, the existing well, it cannot transfer the associated owner state. Instead, the
owner state stays in place but propagation of owner state is done as existing owner state stays in place but propagation of owner state is
specified below done as specified below
o When the current seqid for an owner represents an operation o When the current seqid for an owner represents an operation
associated with the filesystem being migrated, owner status SHOULD associated with the file system being migrated, owner status
be propagated to the destination filesystem. SHOULD be propagated to the destination file system.
o When the current seqid for an owner does not represent an o When the current seqid for an owner does not represent an
operation associated with the filesystem being migrated, owner operation associated with the file system being migrated, owner
status MAY be propagated to the destination filesystem. status MAY be propagated to the destination file system.
o When the owner in question has never been used for an operation o When the owner in question has never been used for an operation
involving the migrated filesystem, the owner information SHOULD involving the migrated file system, the owner information SHOULD
NOT be propagated to the destination filesystem. NOT be propagated to the destination file system.
Note that a server may obey all of the conditions above without the Note that a server may obey all of the conditions above without the
overhead of keeping track of set of filesystems that any particular overhead of keeping track of set of file systems that any particular
owner has been associated with. Consider a situation in which the owner has been associated with. Consider a situation in which the
source server has decided to keep lock-related state associated with source server has decided to keep lock-related state associated with
a filesystem fixed, preparatory to propagating it to the destination a file system fixed, preparatory to propagating it to the destination
filesystem. If a client is free to create new locks associated with file system. If a client is free to create new locks associated with
existing owners on other filesystems, the owner information may be existing owners on other file systems, the owner information may be
propagated to the destination filesystem, even though, at the time propagated to the destination file system, even though, at the time
the filesystem migration is recognized by the client to have the file system migration is recognized by the client to have
occurred, the last operation associated with the owner may not be occurred, the last operation associated with the owner may not be
associated with the migrating filesystem. associated with the migrating file system.
When source server propagates owner-related state associated with When a source server propagates owner-related state associated with
owners that span multiple filesystems, it will propagate the owner owners that span multiple file systems, it will propagate the owner
sequence value to the destination server, while retaining it on the sequence value to the destination server, while retaining it on the
source server, as long as there exists state associated with the source server, as long as there exists state associated with the
owner. When owner information is propagated in this way, source and owner. When owner information is propagated in this way, source and
destination servers start with the same owner sequence value which is destination servers start with the same owner sequence value which is
then updated independently, as the client makes owner-related then updated independently, as the client makes owner-related
requests to the servers. Note that each server will have some period requests to the servers. Note that each server will have some period
in which the associated sequence value for an owner is identical to in which the associated sequence value for an owner is identical to
the one transferred as part of migration. At those times, when a the one transferred as part of migration. At those times, when a
server receives a request with a matching owner sequence value, it server receives a request with a matching owner sequence value, it
MUST NOT respond with the associated stored response if the MUST NOT respond with the associated stored response if the
associated filesystem is not, when the reissued request is received, associated file system is not, when the reissued request is received,
part of the set of filesystems handled by that server. part of the set of file systems handled by that server.
One sort of case may require more complex handling. When multiple One sort of case may require more complex handling. When multiple
filesystem are migrated, in sequence, to a specific destination file system are migrated, in sequence, to a specific destination
server, an owner may be migrated to a destination server, on which it server, an owner may be migrated to a destination server, on which it
was already present, leading to the issue of how the resident owner was already present, leading to the issue of how the resident owner
information and that being newly migrated are to be reconciled. information and that being newly migrated are to be reconciled.
If filesystem migration encounters a situation where owner If file system migration encounters a situation where owner
information needs to be merged, it MAY decline to transfer such information needs to be merged, it MAY decline to transfer such
state, even if it chooses to handle other cases in which locks for a state, even if it chooses to handle other cases in which locks for a
given owner are spread among multiple filesystems. given owner are spread among multiple file systems.
As a way of understanding the situations which need to be addressed As a way of understanding the situations which need to be addressed
when owner information needs to be merged, consider the following when owner information needs to be merged, consider the following
scenario: scenario:
o There is client C and two servers X and Y. There are two o There is client C and two servers X and Y. There are two
clientid's designating C, which we refer to as CX and CY. clientid4's designating C, which are referred to as CX and CY.
o Initially server X supports filesystems F1, F2, F3, and F4. These o Initially server X supports file systems F1, F2, F3, and F4.
will be migrated, one-at-a-time, to server Y. These will be migrated, one-at-a-time, to server Y.
o While these migrations are proceeding, the client makes locking o While these migrations are proceeding, the client makes locking
requests for filesystem F1 through F4 on behalf of owner O (either requests for file system F1 through F4 on behalf of owner O
a lockowner or an openowner), with each request going to X or Y (either a lock-owner or an open-owner), with each request going to
depending on where the relevant filesystem is being supported at X or Y depending on where the relevant file system is being
the time the request is made. supported at the time the request is made.
o Once the first migration event occurs, client C will maintain two o Once the first migration event occurs, client C will maintain two
instances for owner O, one for each server. instances for owner O, one for each server.
o It is always possible that C may make a request of server X o It is always possible that C may make a request of server X
relating to owner O, and before receiving a response, find the relating to owner O, and before receiving a response, find the
target filesystem has moved to Y, and need to re-issue the request target file system has moved to Y, and need to re-issue the
to server Y. request to server Y.
o At the same time, C may make a request of server Y relating to o At the same time, C may make a request of server Y relating to
owner O, and this too may encounter a lost-response situation. owner O, and this too may encounter a lost-response situation.
As a result of such situations, the server needs to provide support As a result of such merger situations, the server will need to
for dealing with retransmission of owner-sequenced requests that provide support for dealing with retransmission of owner-sequenced
diverges from the typical model in which there is support for requests that diverges from the typical model in which there is
retransmission of replies only for a request whose sequence value support for retransmission of replies only for a request whose
exactly matches the last one sent. Such support only needs to be sequence value exactly matches the last one sent. In some
provided for requests issued before the migration event whose status situations, there may be two requests, each of which had the last
as the last by sequence is invalidated by the migration event. sequence when it was issued. As a result of migration and owner
merger, one of those will no longer be the last by sequence.
When servers do support such merger of owner information on the When servers do support such merger of owner information on the
destination server, the following rules are to be adhered to: destination server, the following rules are to be adhered to:
o When an owner sequence value is propagated to a destination server o When an owner sequence value is propagated to a destination server
where it already exists, the resulting sequence value is to be the where it already exists, the resulting sequence value is to be the
greater of the one present on the destination server and the one greater of the one present on the destination server and the one
being propagated as part of migration. being propagated as part of migration.
o In the event that an owner sequence value on a server represents a o In the event that an owner sequence value on a server represents a
request applying to a filesystem currently present on the server, request applying to a file system currently present on the server,
it is not to be rendered invalid simply because that sequence it is not to be rendered invalid simply because that sequence
value is changed as a result of owner information propagation as value is changed as a result of owner information propagation as
part of filesystem migration. Instead, it is retained until it part of file system migration. Instead, it is retained until it
can be deduced that the client in question has received the reply. can be deduced that the client in question has received the reply.
As a result of the operation of these rules, there are three ways in As a result of the operation of these rules, there are three ways in
which we can have more reply data than what is typically present, which there can be more reply data than what is typically present,
i.e. data for a single request per owner whose sequence is the last i.e., data for a single request per owner whose sequence is the last
one received, where the next sequence to be used is one beyond that. one received, where the next sequence to be used is one beyond that.
o When the owner sequence value for a migrating filesystem is o When the owner sequence value for a migrating file system is
greater than the corresponding value on the destination server, greater than the corresponding value on the destination server,
the last request for the owner in effect at the destination server the last request for the owner in effect at the destination server
needs to be retained, even though it is no longer one less the needs to be retained, even though it is no longer one less the
next sequence to be received. next sequence to be received.
o When the owner sequence value for a migrating filesystem is less o When the owner sequence value for a migrating file system is less
than the corresponding value on the destination server the last than the corresponding value on the destination server the
request for the owner in effect on the migrating filesystem needs sequence number for last request for the owner in effect on the
to be retained, even though it is no longer one less the next migrating file system needs to be retained, even though it is no
sequence to be received. longer one than less the next sequence to be received.
o When the owner sequence value for a migrating filesystem is equal o When the owner sequence value for a migrating file system is equal
to the corresponding value on the destination server, one has two to the corresponding value on the destination server, one has two
different "last" requests which both must be retained. The next different "last" requests which both must be retained. The next
sequence value to be used is one beyond the sequence value shared sequence value to be used is one beyond the sequence value shared
by these two requests. by these two requests.
Here are some guidelines as to when servers can drop such additional Here are some guidelines as to when servers can drop such additional
reply data which is created as part of owner information migration. reply data which is created as part of owner information migration.
o The server SHOULD NOT drop this information simply because it o The server SHOULD NOT drop this information simply because it
receives a new sequence value for the owner in question, since receives a new sequence value for the owner in question, since
that request may have been issued before the client was aware of that request may have been issued before the client was aware of
the migration event. the migration event.
o The server SHOULD drop this information if it receives a new o The server SHOULD drop this information if it receives a new
sequence value for the owner in question and the request relates sequence value for the owner in question and the request relates
to the same filesystem. to the same file system.
o The server SHOULD drop the part of this information that relates o The server SHOULD drop the part of this information that relates
to non-migrated filesystems, if it receives a new sequence value to non-migrated file systems, if it receives a new sequence value
for the owner in question and the request relates to a non- for the owner in question and the request relates to a non-
migrated filesystem. migrated file system.
o The server MAY drop this information when it receives a new o The server MAY drop this information when it receives a new
sequence value for the owner in question a considerable period of sequence value for the owner in question a considerable period of
time (more than one or two lease periods) after the migration time (more than one or two lease periods) after the migration
occurs. occurs.
5.1.2. Replication and State 6.1.2. Replication and State
Since client switch-over in the case of replication is not under Since client switch-over in the case of replication is not under
server control, the handling of state is different. In this case, server control, the handling of state is different. In this case,
leases, stateids and client IDs do not have validity across a leases, stateids and client IDs do not have validity across a
transition from one server to another. The client must re-establish transition from one server to another. The client must re-establish
its locks on the new server. This can be compared to the re- its locks on the new server. This can be compared to the re-
establishment of locks by means of reclaim-type requests after a establishment of locks by means of reclaim-type requests after a
server reboot. The difference is that the server has no provision to server reboot. The difference is that the server has no provision to
distinguish requests reclaiming locks from those obtaining new locks distinguish requests reclaiming locks from those obtaining new locks
or to defer the latter. Thus, a client re-establishing a lock on the or to defer the latter. Thus, a client re-establishing a lock on the
new server (by means of a LOCK or OPEN request), may have the new server (by means of a LOCK or OPEN request), may have the
requests denied due to a conflicting lock. Since replication is requests denied due to a conflicting lock. Since replication is
intended for read-only use of filesystems, such denial of locks intended for read-only use of file systems, such denial of locks
should not pose large difficulties in practice. When an attempt to should not pose large difficulties in practice. When an attempt to
re-establish a lock on a new server is denied, the client should re-establish a lock on a new server is denied, the client should
treat the situation as if its original lock had been revoked. treat the situation as if its original lock had been revoked.
5.1.3. Notification of Migrated Lease 6.1.3. Notification of Migrated Lease
A filesystem can be migrated to another server while a client that A file system can be migrated to another server while a client that
has state related to that filesystem is not actively submitting has state related to that file system is not actively submitting
requests to it. In this case, the migration is reported to the requests to it. In this case, the migration is reported to the
client during lease renewal. Lease renewal can occur either client during lease renewal. Lease renewal can occur either
explicitly via a RENEW operation, or implicitly when the client explicitly via a RENEW operation, or implicitly when the client
performs a lease-renewing operation on another filesystem on that performs a lease-renewing operation on another file system on that
server. server.
In order for the client to schedule renewal of leases that may have In order for the client to schedule renewal of leases that may have
been relocated to the new server, the client must find out about been relocated to the new server, the client must find out about
lease relocation before those leases expire. Similarly, when lease relocation before those leases expire. Similarly, when
migration occurs but there has not been transparent state migration, migration occurs but there has not been transparent state migration,
the client needs to find out about the change soon enough to be able the client needs to find out about the change soon enough to be able
to reclaim the lock within the destination server's grace period. To to reclaim the lock within the destination server's grace period. To
accomplish this, all operations which implicitly renew leases for a accomplish this, all operations which implicitly renew leases for a
client (such as OPEN, CLOSE, READ, WRITE, RENEW, LOCK, and others), client (such as OPEN, CLOSE, READ, WRITE, RENEW, LOCK, and others),
will return the error NFS4ERR_LEASE_MOVED if responsibility for any will return the error NFS4ERR_LEASE_MOVED if responsibility for any
of the leases to be renewed has been transferred to a new server. of the leases to be renewed has been transferred to a new server.
Note that when the transfer of responsibility leaves remaining state Note that when the transfer of responsibility leaves remaining state
for that lease on the source server, the lease is renewed just as it for that lease on the source server, the lease is renewed just as it
would have been in the NFS4ERR_OK case, despite returning the error. would have been in the NFS4ERR_OK case, despite returning the error.
The transfer of responsibility happens when the server receives a The transfer of responsibility happens when the server receives a
GETATTR(fs_locations) from the client for each filesystem for which a GETATTR(fs_locations) from the client for each file system for which
lease has been moved to a new server. Normally it does this after a lease has been moved to a new server. Normally it does this after
receiving an NFS4ERR_MOVED for an access to the filesystem but the receiving an NFS4ERR_MOVED for an access to the file system but the
server is not required to verify that this happens in order to server is not required to verify that this happens in order to
terminate the return of NFS4ERR_LEASE_MOVED. By convention, the terminate the return of NFS4ERR_LEASE_MOVED. By convention, the
compounds containing GETATTR(fs_locations) SHOULD include an appended compounds containing GETATTR(fs_locations) SHOULD include an appended
RENEW operation to permit the server to identify the client getting RENEW operation to permit the server to identify the client getting
the information. the information.
Note that the NFS4ERR_LEASE_MOVED error is only required when Note that the NFS4ERR_LEASE_MOVED error is only required when
responsibility for at least one stateid has been affected. In the responsibility for at least one stateid has been affected. In the
case of a null lease, where the only associated state is a clientid, case of a null lease, where the only associated state is a clientid4,
an NFS4ERR_LEASE_MOVED error SHOULD NOT be generated. an NFS4ERR_LEASE_MOVED error SHOULD NOT be generated.
Upon receiving the NFS4ERR_LEASE_MOVED error, a client that supports Upon receiving the NFS4ERR_LEASE_MOVED error, a client that supports
filesystem migration MUST perform the necessary GETATTR operation for file system migration MUST perform the necessary GETATTR operation
each of the filesystems containing state that have been migrated and for each of the file systems containing state that have been migrated
so give the server evidence that it is aware of the migration of the and so give the server evidence that it is aware of the migration of
filesystem. Once the client has done this for all migrated the file system. Once the client has done this for all migrated file
filesystems on which the client holds state, the server MUST resume systems on which the client holds state, the server MUST resume
normal handling of stateful requests from that client. normal handling of stateful requests from that client.
One way in which clients can do this efficiently in the presence of One way in which clients can do this efficiently in the presence of
large numbers of filesystems is described below. This approach large numbers of file systems is described below. This approach
divides the process into two phases, one devoted to finding the divides the process into two phases, one devoted to finding the
migrated filesystems and the second devoted to doing the necessary migrated file systems and the second devoted to doing the necessary
GETATTRs. GETATTRs.
The client can find the migrated filesystems by building and issuing The client can find the migrated file systems by building and issuing
one or more COMPOUND requests, each consisting of a set of PUTFH/ one or more COMPOUND requests, each consisting of a set of PUTFH/
GETFH pairs, each pair using an fh in one of the filesystems in GETFH pairs, each pair using a filehandle in one of the file systems
question. All such COMPOUND requests can be done in parallel. The in question. All such COMPOUND requests can be done in parallel.
successful completion of such a request indicates that none of the The successful completion of such a request indicates that none of
filesystems interrogated have been migrated while termination with the file systems interrogated have been migrated while termination
NFS4ERR_MOVED indicates that the filesystem getting the error has with NFS4ERR_MOVED indicates that the file system getting the error
migrated while those interrogated before it in the same COMPOUND have has migrated while those interrogated before it in the same COMPOUND
not. Those whose interrogation follows the error remain in an have not. Those whose interrogation follows the error remain in an
uncertain state and can be interrogated by restarting the requests uncertain state and can be interrogated by restarting the requests
from after the point at which NFS4ERR_MOVED was returned or by from after the point at which NFS4ERR_MOVED was returned or by
issuing a new set of COMPOUND requests for the filesystems which issuing a new set of COMPOUND requests for the file systems which
remain in an uncertain state. remain in an uncertain state.
Once the migrated filesystems have been found, all that is needed is Once the migrated file systems have been found, all that is needed is
for the client to give evidence to the server that it is aware of the for the client to give evidence to the server that it is aware of the
migrated status of filesystems found by this process, by migrated status of file systems found by this process, by
interrogating the fs_locations attribute for an fh within each of the interrogating the fs_locations attribute for a filehandle within each
migrated filesystems. The client can do this by building and issuing of the migrated file systems. The client can do this by building and
one or more COMPOUND requests, each of which consists of a set of issuing one or more COMPOUND requests, each of which consists of a
PUTFH operations, each followed by a GETATTR of the fs_locations set of PUTFH operations, each followed by a GETATTR of the
attribute. A RENEW is necessary to enable the operations to be fs_locations attribute. A RENEW is necessary to enable the
associated with the lease returning NFS4ERR_LEASE_MOVED. Once the operations to be associated with the lease returning
client has done this for all migrated filesystems on which the client NFS4ERR_LEASE_MOVED. Once the client has done this for all migrated
holds state, the server will resume normal handling of stateful file systems on which the client holds state, the server will resume
requests from that client. normal handling of stateful requests from that client.
In order to support legacy clients that do not handle the In order to support legacy clients that do not handle the
NFS4ERR_LEASE_MOVED error correctly, the server SHOULD time out after NFS4ERR_LEASE_MOVED error correctly, the server SHOULD time out after
a wait of at least two lease periods, at which time it will resume a wait of at least two lease periods, at which time it will resume
normal handling of stateful requests from all clients. If a client normal handling of stateful requests from all clients. If a client
attempts to access the migrated files, the server MUST reply attempts to access the migrated files, the server MUST reply
NFS4ERR_MOVED. In this situation, it is likely that the client would NFS4ERR_MOVED. In this situation, it is likely that the client would
find its lease expired although a server may use "courtesy" locks to find its lease expired although a server may use "courtesy" locks (as
mitigate the issue. described in Section 9.6.3.1 of [RFC7530]) to mitigate the issue.
When the client receives an NFS4ERR_MOVED error, the client can When the client receives an NFS4ERR_MOVED error, the client can
follow the normal process to obtain the destination server follow the normal process to obtain the destination server
information (through the fs_locations attribute) and perform renewal information (through the fs_locations attribute) and perform renewal
of those leases on the new server. If the server has not had state of those leases on the new server. If the server has not had state
transferred to it transparently, the client will receive either transferred to it transparently, the client will receive either
NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from the new server, NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from the new server,
as described above. The client can then recover state information as as described above. The client can then recover state information as
it does in the event of server failure. it does in the event of server failure.
Aside from recovering from a migration, there are other reasons a Aside from recovering from a migration, there are other reasons a
client may wish to retrieve fs_locations information from a server. client may wish to retrieve fs_locations information from a server.
When a server becomes unresponsive, for example, a client may use When a server becomes unresponsive, for example, a client may use
cached fs_locations data to discover an alternate server hosting the cached fs_locations data to discover an alternate server hosting the
same filesystem data. A client may periodically request fs_locations same file system data. A client may periodically request
data from a server in order to keep its cache of fs_locations data fs_locations data from a server in order to keep its cache of
fresh. fs_locations data fresh.
Since a GETATTR(fs_locations) operation would be used for refreshing Since a GETATTR(fs_locations) operation would be used for refreshing
cached fs_locations data, a server could mistake such a request as cached fs_locations data, a server could mistake such a request as
indicating recognition of an NFS4ERR_LEASE_MOVED condition. indicating recognition of an NFS4ERR_LEASE_MOVED condition.
Therefore a compound which is not intended to signal that a client Therefore a compound which is not intended to signal that a client
has recognized a migrated lease SHOULD be prefixed with a guard has recognized a migrated lease SHOULD be prefixed with a guard
operation which fails with NFS4ERR_MOVED if the file handle being operation which fails with NFS4ERR_MOVED if the file handle being
queried is no longer present on the server. The guard can be as queried is no longer present on the server. The guard can be as
simple as a GETFH operation. simple as a GETFH operation.
Though unlikely, it is possible that the target of such a compound Though unlikely, it is possible that the target of such a compound
could be migrated in the time after the guard operation is executed could be migrated in the time after the guard operation is executed
on the server but before the GETATTR(fs_locations) operation is on the server but before the GETATTR(fs_locations) operation is
encountered. When a client issues a GETATTR(fs_locations) operation encountered. When a client issues a GETATTR(fs_locations) operation
as part of a compound not intended to signal recognition of a as part of a compound not intended to signal recognition of a
migrated lease, it SHOULD be prepared to process fs_locations data in migrated lease, it SHOULD be prepared to process fs_locations data in
the reply that shows the current location of the filesystem is gone. the reply that shows the current location of the file system is gone.
5.1.4. Migration and the Lease_time Attribute 6.1.4. Migration and the Lease_time Attribute
In order that the client may appropriately manage its leases in the In order that the client may appropriately manage its leases in the
case of migration, the destination server must establish proper case of migration, the destination server must establish proper
values for the lease_time attribute. values for the lease_time attribute.
When state is transferred transparently, that state should include When state is transferred transparently, that state should include
the correct value of the lease_time attribute. The lease_time the correct value of the lease_time attribute. The lease_time
attribute on the destination server must never be less than that on attribute on the destination server must never be less than that on
the source since this would result in premature expiration of leases the source since this would result in premature expiration of leases
granted by the source server. Upon migration in which state is granted by the source server. Upon migration in which state is
skipping to change at page 34, line 32 skipping to change at page 39, line 5
needs to reclaim or re-obtain its locks), the client should fetch the needs to reclaim or re-obtain its locks), the client should fetch the
value of lease_time on the new (i.e., destination) server, and use it value of lease_time on the new (i.e., destination) server, and use it
for subsequent locking requests. However the server must respect a for subsequent locking requests. However the server must respect a
grace period at least as long as the lease_time on the source server, grace period at least as long as the lease_time on the source server,
in order to ensure that clients have ample time to reclaim their in order to ensure that clients have ample time to reclaim their
locks before potentially conflicting non-reclaimed locks are granted. locks before potentially conflicting non-reclaimed locks are granted.
The means by which the new server obtains the value of lease_time on The means by which the new server obtains the value of lease_time on
the old server is left to the server implementations. It is not the old server is left to the server implementations. It is not
specified by the NFS version 4.0 protocol. specified by the NFS version 4.0 protocol.
6. Server Implementation Considerations 7. Server Implementation Considerations
This chapter provides suggestions to help server implementers deal This chapter provides suggestions to help server implementers deal
with issues involved in the transparent transfer of filesystem- with issues involved in the transparent transfer of file system-
related data between servers. Servers are not obliged to follow related data between servers. Servers are not obliged to follow
these suggestions, but should be sure that their approach to the these suggestions, but should be sure that their approach to the
issues handle all the potential problems addressed below. issues handle all the potential problems addressed below.
6.1. Relation of Locking State Transfer to Other Aspects of Filesystem 7.1. Relation of Locking State Transfer to Other Aspects of File System
Motion Motion
In many cases, state transfer will be part of a larger function In many cases, state transfer will be part of a larger function
wherein the contents of a filesystem are transferred from server to wherein the contents of a file system are transferred from server to
server. Although specifics will vary with the implementation, the server. Although specifics will vary with the implementation, the
relation between the transfer of persistent file data and metadata relation between the transfer of persistent file data and metadata
and the transfer of state will typically be described by one of the and the transfer of state will typically be described by one of the
cases below. cases below.
o In some implementations, access to the on-disk contents of a o In some implementations, access to the on-disk contents of a file
filesystem can be transferred from server to server by making the system can be transferred from server to server by making the
storage devices on which the filesystem resides physically storage devices on which the file system resides physically
accessible from multiple servers, and transferring the right and accessible from multiple servers, and transferring the right and
responsibility for handling that filesystem from server to server. responsibility for handling that file system from server to
server.
In such implementations, the transfer of locking state happens on In such implementations, the transfer of locking state happens on
its own, as described in Section 6.2. The transfer of physical its own, as described in Section 7.2. The transfer of physical
access to the filesystem happens after the locking state is access to the file system happens after the locking state is
transferred and before any subsequent access to the filesystem. transferred and before any subsequent access to the file system.
In cases where such transfer is not instantaneous, there will be a In cases where such transfer is not instantaneous, there will be a
period in which all operations on the filesystem are held off, period in which all operations on the file system are held off,
either by having the operations themselves return NFS4ERR_DELAY, either by having the operations themselves return NFS4ERR_DELAY,
or, where this is not allowed, by using the techniques described or, where this is not allowed, by using the techniques described
below in Section 6.2. below in Section 7.2.
o In other implementations, filesystem data and metadata must be o In other implementations, file system data and metadata must be
copied from the server where it has existed to the destination copied from the server where it has existed to the destination
server. Because of the typical amounts of data involved, it is server. Because of the typical amounts of data involved, it is
generally not practical to hold off access to the filesystem while generally not practical to hold off access to the file system
this transfer is going on. Normal access to the filesystem, while this transfer is going on. Normal access to the file
including modifying operations, will generally happen while the system, including modifying operations, will generally happen
transfer is going on. while the transfer is going on.
Eventually the filesystem copying process will complete. At this Eventually the file system copying process will complete. At this
point, there will be two valid copies of the filesystem, one on point, there will be two valid copies of the file system, one on
each of the source and destination servers. Servers may maintain each of the source and destination servers. Servers may maintain
that state of affairs by making sure that each modification to that state of affairs by making sure that each modification to
filesystem data is done on both the source and destination file system data is done on both the source and destination
servers. servers.
Although the transfer of locking state can begin before the above Although the transfer of locking state can begin before the above
state of affairs is reached, servers will often wait until it is state of affairs is reached, servers will often wait until it is
arrived at to begin transfer of locking state. Once the transfer arrived at to begin transfer of locking state. Once the transfer
of locking state is completed, as described in the section below, of locking state is completed, as described in the section below,
clients may be notified of the migration event and access the clients may be notified of the migration event and access the
destination filesystem on the destination server. destination file system on the destination server.
o Another case in which filesystem data and metadata must be copied o Another case in which file system data and metadata must be copied
from server to server involves a variant of the pattern above. In from server to server involves a variant of the pattern above. In
cases in which a single filesystem moves between or among a small cases in which a single file system moves between or among a small
set of servers, it will transition to a server on which a previous set of servers, it will transition to a server on which a previous
instantiation of that same filesystem existed before. In such instantiation of that same file system existed before. In such
cases, it is often more efficient to update the previous cases, it is often more efficient to update the previous file
filesystem instance to reflect changes made while the active system instance to reflect changes made while the active file
filesystem was residing elsewhere, rather than copying the system was residing elsewhere, rather than copying the file system
filesystem data anew. data anew.
In such cases, the copying of filesystem data and metadata is In such cases, the copying of file system data and metadata is
replaced by a process which validates each visible filesystem replaced by a process which validates each visible file system
object, copying new objects and updating those that have changed object, copying new objects and updating those that have changed
since the filesystem was last present on the destination server. since the file system was last present on the destination server.
Although this process is generally shorter than a complete copy, Although this process is generally shorter than a complete copy,
it is generally long enough that it is not practical to hold off it is generally long enough that it is not practical to hold off
access to the filesystem while this update is going on. access to the file system while this update is going on.
Eventually the filesystem updating process will complete. At this Eventually the file system updating process will complete. At
point, there will be two valid copies of the filesystem, one on this point, there will be two valid copies of the file system, one
each of the source and destination servers. Servers may maintain on each of the source and destination servers. Servers may
that state of affairs just as is done in the previous case. maintain that state of affairs just as is done in the previous
Similarly, the transfer of locking state, once it is complete, case. Similarly, the transfer of locking state, once it is
allows the clients to be notified of the migration event and complete, allows the clients to be notified of the migration event
access the destination filesystem on the destination server. and access the destination file system on the destination server.
6.2. Preventing Locking State Modification During Transfer 7.2. Preventing Locking State Modification During Transfer
When transferring locking state from the source to a destination When transferring locking state from the source to a destination
server, there will be occasions when the source server will need to server, there will be occasions when the source server will need to
prevent operations that modify the state being transferred. For prevent operations that modify the state being transferred. For
example, if the locking state at time T is sent to the destination example, if the locking state at time T is sent to the destination
server, any state change that occurs on the source server after that server, any state change that occurs on the source server after that
time but before the filesystem transfer is made effective will mean time but before the file system transfer is made effective will mean
that the state on the destination server will differ from that on the that the state on the destination server will differ from that on the
source server, which matches what the client would expect to see. source server, which matches what the client would expect to see.
In general, a server can prevent some set of server-maintained data In general, a server can prevent some set of server-maintained data
from changing by returning NFS4ERR_DELAY on operations which attempt from changing by returning NFS4ERR_DELAY on operations which attempt
to change that data. In the case of locking state for NFSv4.0, there to change that data. In the case of locking state for NFSv4.0, there
are two specific issues that might interfere: are two specific issues that might interfere:
o Returning NFS4ERR_DELAY will not prevent state from changing in o Returning NFS4ERR_DELAY will not prevent state from changing in
that owner-based sequence values will still change, even though that owner-based sequence values will still change, even though
NFS4ERR_DELAY is returned. For example OPEN and LOCK will change NFS4ERR_DELAY is returned. For example OPEN and LOCK will change
state (in the form of owner seqid values) even when they return state (in the form of owner seqid values) even when they return
NFS4ERR_DELAY. NFS4ERR_DELAY.
o Some operations which modify locking state are not allowed to o Some operations which modify locking state are not allowed to
return NFS4ERR_DELAY. return NFS4ERR_DELAY (i.e., OPEN_CONFIRM, RELEASE_LOCKOWNER, and
RENEW)
Note that the first problem and many instances of the second can be Note that the first problem and most instances of the second can be
addressed by returning NFS4ERR_DELAY on the operations that establish addressed by returning NFS4ERR_DELAY on the operations that establish
a filehandle within the target as one of the filehandles associated a filehandle within the target as one of the filehandles associated
with the request, i.e. as either the current or saved filehandle. with the request, i.e., as either the current or saved filehandle.
This would require returning NFS4ERR_DELAY under the following This would require returning NFS4ERR_DELAY under the following
circumstances: circumstances:
o On a PUTFH that specifies a filehandle within the target o On a PUTFH that specifies a filehandle within the target file
filesystem. system.
o On a LOOKUP or LOOKUPP that crosses into the target filesystem. o On a LOOKUP or LOOKUPP that crosses into the target file system.
As a result of doing this, OPEN_CONFIRM is dealt with, leaving only
RELEASE_LOCKOWNER and RENEW still to be dealt with.
Note that if the server establishes and maintains a situation in Note that if the server establishes and maintains a situation in
which no request has, as either the current or saved filehandle, a which no request has, as either the current or saved filehandle, a
filehandle within the target filesystem, no special handling of filehandle within the target file system, no special handling of
SAVEFH or RESTOREFH is required. Thus the fact that these operations SAVEFH or RESTOREFH is required. Thus the fact that these operations
cannot return NFS4ERR_DELAY is not a problem since neither will cannot return NFS4ERR_DELAY is not a problem since neither will
establish a filehandle in the target filesystem as the current establish a filehandle in the target file system as the current
filehandle. filehandle.
If the server is to establish the situation described above, it may If the server is to establish the situation described above, it may
have to take special note of long-running requests which started have to take special note of long-running requests which started
before state migration. Part of any solution to this issue will before state migration. Part of any solution to this issue will
involve distinguishing two separate points in time at which handling involve distinguishing two separate points in time at which handling
for the target filesystem will change. Let us distinguish; for the target file system will change. Let us distinguish;
o A time T after which the previously mentioned operations will o A time T after which the previously mentioned operations will
return NFS4ERR_DELAY. return NFS4ERR_DELAY.
o A later time T' at which the server can consider filesystem o A later time T' at which the server can consider file system
locking state fixed, making it possible for it to be sent to the locking state fixed, making it possible for it to be sent to the
destination server. destination server.
For a server to decide on T', it must ensure that requests started For a server to decide on T', it must ensure that requests started
before T, cannot change target filesystem locking state, given that before T, cannot change target file system locking state, given that
all those started after T are dealt with by returning NFS4ERR_DELAY all those started after T are dealt with by returning NFS4ERR_DELAY
upon setting filehandles within the target filesystem. Among the upon setting filehandles within the target file system. Among the
ways of doing this are: ways of doing this are:
o Keeping track of the earliest request started which is still in o Keeping track of the earliest request started which is still in
execution (for example, by keeping a list of active requests execution (for example, by keeping a list of active requests
ordered by request start time). The server can then define T' to ordered by request start time). Requests that started before and
be the first time at which the earliest-started active request are still in progress at time T may potentially affect the locking
started after time T. state; once the starting time of the earliest-started active
request is later than T, the starting time of the first such
request can be chosen as T' by the server since any request in
progress after T' started after time T. Accordingly it would not
have been allowed to change locking state for the migrating file
system and would have returned NFS4ERR_DELAY had it tried to make
a change.
o Keeping track of the count of requests, started before time T o Keeping track of the count of requests, started before time T
which have a filehandle within the target filesystem as either the which have a filehandle within the target file system as either
current or saved filehandle. The server can then define T' to be the current or saved filehandle. The server can then define T' to
the first time after T at which the count is zero. be the first time after T at which the count is zero.
The set of operations that change locking state include two that The set of operations that change locking state include two that
cannot be dealt with by the above approach, because they are not cannot be dealt with by the above approach, because they are not
filesystem-specific and do not use a current filehandle as an specific to a particular file system and do not use a current
implicit parameter. filehandle as an implicit parameter.
o RENEW can be dealt with by applying the renewal to state for non- o RENEW can be dealt with by applying the renewal to state for non-
transitioning filesystems. The effect of renewal for the transitioning file systems. The effect of renewal for the
transitioning filesystem can be ignored, as long as the servers transitioning file system can be ignored, as long as the servers
make sure that the lease on the destination server has an make sure that the lease on the destination server has an
expiration time that is no earlier than the latest renewal done on expiration time that is no earlier than the latest renewal done on
the source server. This can be easily accomplished by making the the source server. This can be easily accomplished by making the
lease expiration on the destination server equal to the time the lease expiration on the destination server equal to the time the
state transfer was completed plus the lease period. state transfer was completed plus the lease period.
o RELEASE_LOCKOWNER can be handled by propagating the fact of the o RELEASE_LOCKOWNER can be handled by propagating the fact of the
lockowner deletion (e.g. by using an RPC) to the destination lock-owner deletion (e.g., by using an RPC) to the destination
server. Such a propagation RPC can be done as part of the server. Such a propagation RPC can be done as part of the
operation or the existence of the deletion can be recorded locally operation or the existence of the deletion can be recorded locally
and propagation of owner deletions to the destination server done and propagation of owner deletions to the destination server done
as a batch later. In either case, the actual deletions on the as a batch later. In either case, the actual deletions on the
destination server have to be delayed until all of the other state destination server have to be delayed until all of the other state
information has been transferred. information has been transferred.
Alternatively, RELEASE_LOCKOWNER can be dealt with by returning Alternatively, RELEASE_LOCKOWNER can be dealt with by returning
NFS4ERR_DELAY. In order to avoid compatibility issues for clients NFS4ERR_DELAY. In order to avoid compatibility issues for clients
not prepared to accept NFS4ERR_DELAY in response to not prepared to accept NFS4ERR_DELAY in response to
RELEASE_LOCKOWNER, care must be exercised. (See Section 7.3 for RELEASE_LOCKOWNER, care must be exercised. (See Section 8.3 for
details.) details.)
The approach outlined above, wherein NFS$ERR_DELAY is returned based The approach outlined above, wherein NFS$ERR_DELAY is returned based
primarily on the use of current and saved filehandles in the primarily on the use of current and saved filehandles in the file
filesystem, prevents all reference to the transitioning filesystem, system, prevents all reference to the transitioning file system,
rather than limiting the delayed operations to those that change rather than limiting the delayed operations to those that change
locking state on the transitioning filesystem. Because of this, locking state on the transitioning file system. Because of this,
servers may choose to limit the time during which this broad approach servers may choose to limit the time during which this broad approach
is used by adopting a layered approach to the issue. is used by adopting a layered approach to the issue.
o During the preparatory phase, operations that change, create, or o During the preparatory phase, operations that change, create, or
destroy locks or modify the valid set of stateids will return destroy locks or modify the valid set of stateids will return
NFS4ERR_DELAY. During this phase, owner-associated seqids may NFS4ERR_DELAY. During this phase, owner-associated seqids may
change, and the identity of the filesystem associated with the change, and the identity of the file system associated with the
last request for a given owner may change as well. Also, last request for a given owner may change as well. Also,
RELEASE_LOCKOWNER operations may be processed without returning RELEASE_LOCKOWNER operations may be processed without returning
NFS4ERR_DELAY as long as the fact of the lockowner deletion is NFS4ERR_DELAY as long as the fact of the lock-owner deletion is
recorded locally for later transmission. recorded locally for later transmission.
o During the restrictive phase, operations that change locking state o During the restrictive phase, operations that change locking state
for the filesystem in transition are prevented by returning for the file system in transition are prevented by returning
NFS4ERR_DELAY on any attempt to make a filehandle within that NFS4ERR_DELAY on any attempt to make a filehandle within that file
filesystem either the current or saved filehandle for a request. system either the current or saved filehandle for a request.
RELEASE_LOCKOWNER operations may return NFS4ERR_DELAY, but if they RELEASE_LOCKOWNER operations may return NFS4ERR_DELAY, but if they
are processed, the lockowner deletion needs to be communicated are processed, the lock-owner deletion needs to be communicated
immediately to the destination server. immediately to the destination server.
A possible sequence would be the following. A possible sequence would be the following.
o The server enters the preparatory phase for the transitioning o The server enters the preparatory phase for the transitioning file
filesystem. system.
o At this point locking state, including stateids, locks, owner o At this point locking state, including stateids, locks, owner
strings are transferred to the destination server. The seqids strings are transferred to the destination server. The seqids
associated with owners are either not transferred, or transferred associated with owners are either not transferred, or transferred
on a provisional basis, subject to later change. on a provisional basis, subject to later change.
o After the above has been transferred, the server may enter the o After the above has been transferred, the server may enter the
restrictive phase for the filesystem. restrictive phase for the file system.
o At this point, the updated seqid values may be sent to the o At this point, the updated seqid values may be sent to the
destination server. destination server.
Reporting regarding pending owner deletions (as a result of Reporting regarding pending owner deletions (as a result of
RELEASE_LOCKOWNER operations) can be communicated at the same RELEASE_LOCKOWNER operations) can be communicated at the same
time. time.
o Once it is known that all of this information has been transferred o Once it is known that all of this information has been transferred
to the destination server, and there are no pending to the destination server, and there are no pending
RELEASE_LOCKOWNER notifications outstanding, the source server may RELEASE_LOCKOWNER notifications outstanding, the source server may
treat the filesystem transition as having occurred and return treat the file system transition as having occurred and return
NFS4ERR_MOVED when an attempt is made to access it. NFS4ERR_MOVED when an attempt is made to access it.
7. Additional Changes 8. Additional Changes
This chapter contains a number of items which relate to the changes This chapter contains a number of items which relate to the changes
in the chapters above, but which, for one reason or another, exist in in the chapters above, but which, for one reason or another, exist in
different portions of the specification to be updated. different portions of the specification to be updated.
7.1. Summary of Additional Changes from Previous Documents 8.1. Summary of Additional Changes from Previous Documents
We summarize here all the remaining changes, not included in the two
main chapters.
o New definition of the CLID_INUSE error.
o A revised description of SETCLIENTID, which brings the description Summarized here are all the remaining changes, not included in the
into sync with the rest of the spec regarding CLID_INUSE. two main chapters.
o A revision to the Security Considerations section, indicating why o New definition of the error NFS4ERR_CLID_INUSE, appearing in
integrity protection is needed for the SETCLIENTID operation. Section 8.2. This replaces the definition in Section 13.1.10.1 in
[RFC7530].
o A revision of the error definitions chapter to allow o A revision of the error definitions chapter to allow
RELEASE_LOCKOWNER to return NFS4ERR_DELAY, with appropriate RELEASE_LOCKOWNER to return NFS4ERR_DELAY, with appropriate
constraints to assure interoperability with clients not expecting constraints to assure interoperability with clients not expecting
this error to be returned. this error to be returned. These changes are discussed in
Section 8.2 and modify the error tables in Sections 13.2 and 13.4
in [RFC7530].
7.2. NFS4ERR_CLID_INUSE definition o A revised description of SETCLIENTID, appearing in Section 8.4.
This brings the description into sync with the rest of the spec
regarding NFS4ERR_CLID_INUSE. The revised description replace the
one in Section 16.33 of [RFC7530].
o Some security-related changes appear in Sections 8.5 and 8.6. The
Security Considerations section of this document (Section 9)
describes the effect on the corresponding section (Section 19) in
[RFC7530].
8.2. NFS4ERR_CLID_INUSE definition
The definition of this error is now as follows The definition of this error is now as follows
The SETCLIENTID operation has found that the id string within the The SETCLIENTID operation has found that the id string within the
specified nfs_client_id4 was previously presented with a different specified nfs_client_id4 was previously presented with a different
principal and that client instance currently holds an active principal and that client instance currently holds an active
lease. A server MAY return this error if the same principal is lease. A server MAY return this error if the same principal is
used but a change in authentication flavor gives good reason to used but a change in authentication flavor gives good reason to
reject the new SETCLIENTID operation as not bona fide. reject the new SETCLIENTID operation as not bona fide.
7.3. NFS4ERR_DELAY return from RELEASE_LOCKOWNER 8.3. NFS4ERR_DELAY return from RELEASE_LOCKOWNER
The existing error tables should be considered modified to allow The existing error tables should be considered modified to allow
NFS4ERR_DELAY to be returned by RELEASE_LOCKOWNER. However, the NFS4ERR_DELAY to be returned by RELEASE_LOCKOWNER. However, the
scope of this addition is limited and is not to be considered as scope of this addition is limited and is not to be considered as
making this error return generally acceptable. making this error return generally acceptable.
It needs to be made clear that servers may not return this error to It needs to be made clear that servers may not return this error to
clients not prepared to support filesystem migration. Such clients clients not prepared to support file system migration. Such clients
may be following the error specifications in [RFC7530] and so might may be following the error specifications in [RFC7530] and so might
not expect NFS4ERR_DELAY to be returned on RELEASE_LOCKOWNER. not expect NFS4ERR_DELAY to be returned on RELEASE_LOCKOWNER.
The following constraint applies to this additional error return, as The following constraint applies to this additional error return, as
if it were a note appearing together with the newly allowed error if it were a note appearing together with the newly allowed error
code: code:
In order to make server state fixed for a filesystem being In order to make server state fixed for a file system being
migrated, a server MAY return NFS4ERR_DELAY in response to a migrated, a server MAY return NFS4ERR_DELAY in response to a
RELEASE_LOCKOWNER that will affect locking state being propagated RELEASE_LOCKOWNER that will affect locking state being propagated
to a destination server. The source server MUST NOT do so unless to a destination server. The source server MUST NOT do so unless
it is likely that it will later return NFS4ERR_MOVED for the it is likely that it will later return NFS4ERR_MOVED for the file
filesystem in question. system in question.
In the context of lockowner release, the set of filesystems such In the context of lock-owner release, the set of file systems such
that server state being made fixed can result in NFS4ERR_DELAY that server state being made fixed can result in NFS4ERR_DELAY
must include the filesystem on which the operation associated with must include the file system on which the operation associated
the current lockowner seqid was performed. with the current lock-owner seqid was performed.
In addition, this set may include other filesystems on which an In addition, this set may include other file systems on which an
operation associated with an earlier seqid for the current operation associated with an earlier seqid for the current lock-
lockowner seqid was performed, since servers will have to deal owner seqid was performed, since servers will have to deal with
with the issue of an owner being used in succession for multiple the issue of an owner being used in succession for multiple file
filesystems. systems.
Thus, a client that is prepared to receive NFS4ERR_MOVED after Thus, if a client that is prepared to receive NFS4ERR_MOVED after
creating state associated with a given filesystem, it also needs creating state associated with a given file system, it also needs
to be prepared to receive NFS4ERR_DELAY in response to to be prepared to receive NFS4ERR_DELAY in response to
RELEASE_LOCKOWNER, if it has used that owner in connection with a RELEASE_LOCKOWNER, if it has used that owner in connection with a
file on that filesystem. file on that file system.
7.4. Operation 35: SETCLIENTID - Negotiate Client ID 8.4. Operation 35: SETCLIENTID - Negotiate Client ID
7.4.1. SYNOPSIS 8.4.1. SYNOPSIS
client, callback, callback_ident -> clientid, setclientid_confirm client, callback, callback_ident -> clientid, setclientid_confirm
7.4.2. ARGUMENT 8.4.2. ARGUMENT
struct SETCLIENTID4args { struct SETCLIENTID4args {
nfs_client_id4 client; nfs_client_id4 client;
cb_client4 callback; cb_client4 callback;
uint32_t callback_ident; uint32_t callback_ident;
}; };
7.4.3. RESULT 8.4.3. RESULT
struct SETCLIENTID4resok { struct SETCLIENTID4resok {
clientid4 clientid; clientid4 clientid;
verifier4 setclientid_confirm; verifier4 setclientid_confirm;
}; };
union SETCLIENTID4res switch (nfsstat4 status) { union SETCLIENTID4res switch (nfsstat4 status) {
case NFS4_OK: case NFS4_OK:
SETCLIENTID4resok resok4; SETCLIENTID4resok resok4;
case NFS4ERR_CLID_INUSE: case NFS4ERR_CLID_INUSE:
clientaddr4 client_using; clientaddr4 client_using;
default: default:
void; void;
}; };
7.4.4. DESCRIPTION 8.4.4. DESCRIPTION
The client uses the SETCLIENTID operation to notify the server of its The client uses the SETCLIENTID operation to notify the server of its
intention to use a particular client identifier, callback, and intention to use a particular client identifier, callback, and
callback_ident for subsequent requests that entail creating lock, callback_ident for subsequent requests that entail creating lock,
share reservation, and delegation state on the server. Upon share reservation, and delegation state on the server. Upon
successful completion the server will return a shorthand client ID successful completion the server will return a shorthand client ID
which, if confirmed via a separate step, will be used in subsequent which, if confirmed via a separate step, will be used in subsequent
file locking and file open requests. Confirmation of the client ID file locking and file open requests. Confirmation of the client ID
must be done via the SETCLIENTID_CONFIRM operation to return the must be done via the SETCLIENTID_CONFIRM operation to return the
client ID and setclientid_confirm values, as verifiers, to the client ID and setclientid_confirm values, as verifiers, to the
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The callback information provided in this operation will be used if The callback information provided in this operation will be used if
the client is provided an open delegation at a future point. the client is provided an open delegation at a future point.
Therefore, the client must correctly reflect the program and port Therefore, the client must correctly reflect the program and port
numbers for the callback program at the time SETCLIENTID is used. numbers for the callback program at the time SETCLIENTID is used.
The callback_ident value is used by the server on the callback. The The callback_ident value is used by the server on the callback. The
client can leverage the callback_ident to eliminate the need for more client can leverage the callback_ident to eliminate the need for more
than one callback RPC program number, while still being able to than one callback RPC program number, while still being able to
determine which server is initiating the callback. determine which server is initiating the callback.
7.4.5. IMPLEMENTATION 8.4.5. IMPLEMENTATION
To understand how to implement SETCLIENTID, make the following To specify the implementation of SETCLIENTID, the following notations
notations. Let: are used.
Let:
x be the value of the client.id subfield of the SETCLIENTID4args x be the value of the client.id subfield of the SETCLIENTID4args
structure. structure.
v be the value of the client.verifier subfield of the v be the value of the client.verifier subfield of the
SETCLIENTID4args structure. SETCLIENTID4args structure.
c be the value of the client ID field returned in the c be the value of the client ID field returned in the
SETCLIENTID4resok structure. SETCLIENTID4resok structure.
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callback_ident fields of the SETCLIENTID4args structure. callback_ident fields of the SETCLIENTID4args structure.
s be the setclientid_confirm value returned in the SETCLIENTID4resok s be the setclientid_confirm value returned in the SETCLIENTID4resok
structure. structure.
{ v, x, c, k, s } be a quintuple for a client record. A client { v, x, c, k, s } be a quintuple for a client record. A client
record is confirmed if there has been a SETCLIENTID_CONFIRM record is confirmed if there has been a SETCLIENTID_CONFIRM
operation to confirm it. Otherwise it is unconfirmed. An operation to confirm it. Otherwise it is unconfirmed. An
unconfirmed record is established by a SETCLIENTID call. unconfirmed record is established by a SETCLIENTID call.
7.4.5.1. IMPLEMENTATION (Preparatory Phase) 8.4.5.1. IMPLEMENTATION (Preparatory Phase)
Since SETCLIENTID is a non-idempotent operation, let us assume that Since SETCLIENTID is a non-idempotent operation, our treatment
the server is implementing the duplicate request cache (DRC). assumes use of a duplicate request cache (DRC). For a discussion of
the DRC, see Section 9.1.7 of [RFC7530].
When the server gets a SETCLIENTID { v, x, k } request, it first does When the server gets a SETCLIENTID { v, x, k } request, it first does
a number of preliminary checks as listed below before proceeding to a number of preliminary checks as listed below before proceeding to
the main part of SETCLIENTID processing. the main part of SETCLIENTID processing.
o It first looks up the request in the DRC. If there is a hit, it o It first looks up the request in the DRC. If there is a hit, it
returns the result cached in the DRC. The server does NOT remove returns the result cached in the DRC. The server does NOT remove
client state (locks, shares, delegations) nor does it modify any client state (locks, shares, delegations) nor does it modify any
recorded callback and callback_ident information for client { x }. recorded callback and callback_ident information for client { x }.
The server now proceeds to the main part of SETCLIENTID.
o Otherwise (i.e. in the case of any DRC miss), the server takes the o Otherwise (i.e., in the case of any DRC miss), the server takes
client id string x, and searches for confirmed client records for the client id string x, and searches for confirmed client records
x that the server may have recorded from previous SETCLIENTID for x that the server may have recorded from previous SETCLIENTID
calls. If there are no such, or if all such records have a calls. If there are no such, or if all such records have a
recorded principal which matches that of the current request's recorded principal which matches that of the current request's
principal, then principal, then the preparatory phase proceeds as follows.
o If there is a confirmed client record with a matching client id * If there is a confirmed client record with a matching client id
string and a non-matching principal, the server checks the current string and a non-matching principal, the server checks the
state of the associated lease. If there is no associated state current state of the associated lease. If there is no
for the lease, or the lease has expired, the server proceeds to associated state for the lease, or the lease has expired, the
the main part of SETCLIENTID server proceeds to the main part of SETCLIENTID.
o Otherwise, the server is being asked to do a SETCLIENTID for a * Otherwise, the server is being asked to do a SETCLIENTID for a
client by a non-matching principal while there is active state and client by a non-matching principal while there is active state.
the server rejects the SETCLIENTID request returning an In this case, the server rejects the SETCLIENTID request
NFS4ERR_CLID_INUSE error, since use of a single client with returning an NFS4ERR_CLID_INUSE error, since use of a single
multiple principals is not allowed. Note that even though the client with multiple principals is not allowed. Note that even
previously used clientaddr is returned with this error, the use of though the previously used clientaddr4 is returned with this
the same id string with multiple clientaddr's is not prohibited, error, the use of the same id string with multiple
while its use with multiple principals is prohibited. clientaddr4's is not prohibited, while its use with multiple
principals is prohibited.
7.4.5.2. IMPLEMENTATION (Main Phase) 8.4.5.2. IMPLEMENTATION (Main Phase)
If the SETCLIENTID has not been dealt with by DRC processing, and has If the SETCLIENTID has not been dealt with by DRC processing, and has
not been rejected with an NFS4ERR_CLID_INUSE error, then the main not been rejected with an NFS4ERR_CLID_INUSE error, then the main
part of SETCLIENTID processing proceeds, as described below. part of SETCLIENTID processing proceeds, as described below.
o The server checks if it has recorded a confirmed record for { v, o The server checks if it has recorded a confirmed record for { v,
x, c, l, s }, where l may or may not equal k. If so, and since x, c, l, s }, where l may or may not equal k. If so, and since
the id verifier v of the request matches that which is confirmed the id verifier v of the request matches that which is confirmed
and recorded, the server treats this as a probable callback and recorded, the server treats this as a probable callback
information update and records an unconfirmed { v, x, c, k, t } information update and records an unconfirmed { v, x, c, k, t }
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The server returns { d, t }. The server returns { d, t }.
The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
{ d, t }. The server does NOT remove client (lock/share/ { d, t }. The server does NOT remove client (lock/share/
delegation) state for x. delegation) state for x.
The server generates the clientid and setclientid_confirm values and The server generates the clientid and setclientid_confirm values and
must take care to ensure that these values are extremely unlikely to must take care to ensure that these values are extremely unlikely to
ever be regenerated. ever be regenerated.
7.5. Security Considerations for Inter-server Information Transfer 8.5. Security Considerations for Inter-server Information Transfer
Although the means by which the source and destination server Although the means by which the source and destination server
communicate is not specified by NFSv4.0, the following security- communicate is not specified by NFSv4.0, the following security-
related requirements for inter-server communication should be noted. related considerations for inter-server communication should be
noted.
o Communication between source and destination servers needs to be o Communication between source and destination servers needs to be
carried out in a secure manner, either on a private network, or carried out in a secure manner, with protection against deliberate
using a security mechanism that ensures privacy. modification of data in transit provided either by use of private
network, or by using a security mechanism that ensures integrity.
In many cases, privacy will also be required, requiring a
strengthened security mechanism if a private network is not used.
o Effective implementation of the filesystem migration function o Effective implementation of the file system migration function
requires that a trust relationship exist between source and requires that a trust relationship exist between source and
destination servers. destination servers. The details of that trust relationship
depend on the specifics of the inter-server transfer protocol,
which is outside the scope of this specification.
o The source server may communicate to the destination sever o The source server may communicate to the destination server
security-related information to be used to make more rigorous the security-related information in order to allow it to more
validation of client's identity. For example, the destination rigorously validate clients' identity. For example, the
server might reject a SETCLIENTID done with a different principal destination server might reject a SETCLIENTID done with a
or with a different IP address than was done previously by the different principal or with a different IP address than was done
client on the source server. However, the destination server MUST previously by the client on the source server. However, the
NOT use this information to allow any operation to be performed by destination server MUST NOT use this information to allow any
the client that would not be allowed otherwise. operation to be performed by the client that would not be allowed
otherwise.
7.6. Security Considerations Revision 8.6. Security Considerations Revision
The last paragraph of the "Security Considerations" section should be The penultimate paragraph of Section 19 of [RFC7530] should be
revised to read as follows: revised to read as follows:
Because the operations SETCLIENTID/SETCLIENTID_CONFIRM are Because the operations SETCLIENTID/SETCLIENTID_CONFIRM are
responsible for the release of client state, it is imperative that responsible for the release of client state, it is imperative that
the principal used for these operations is checked against and the principal used for these operations is checked against and
match the previous use of these operations. In addition, use of match the previous use of these operations. In addition, use of
integrity protection is desirable on the SETCLIENTID operation, to integrity protection is desirable on the SETCLIENTID operation, to
prevent an attack whereby a change in the boot verifier forces an prevent an attack whereby a change in the boot instance id
undesired loss of client state. See the section "Client Identity (verifier) forces an undesired loss of client state. See the
Definition" for further discussion. Section 5 for further discussion.
8. Security Considerations
Is to be modified as specified in Section 7.6. 9. Security Considerations
In addition, the material in Section 7.5 should be noted. The security considerations of [RFC7530] remain appropriate with the
exception of the modification to the penultimate paragraph specified
in Section 8.6 of this document and the addition of the material in
Section 8.5.
9. IANA Considerations 10. IANA Considerations
This document does not require actions by IANA. This document does not require actions by IANA.
10. References 11. References
10.1. Normative References 11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC7530] Haynes, T. and D. Noveck, "Network File System (NFS) [RFC7530] Haynes, T., Ed. and D. Noveck, Ed., "Network File System
Version 4 Protocol", RFC 7530, March 2015. (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
March 2015, <http://www.rfc-editor.org/info/rfc7530>.
10.2. Informative References 11.2. Informative References
[info-migr] [info-migr]
Noveck, D., Ed., Shivam, P., Lever, C., and B. Baker, Noveck, D., Ed., Shivam, P., Lever, C., and B. Baker,
"NFSv4 migration: Implementation experience and spec "NFSv4 migration: Implementation experience and spec
issues to resolve", March 2015, <http://www.ietf.org/id/ issues to resolve", March 2015, <http://www.ietf.org/id/
draft-ietf-nfsv4-migration-issues-07.txt>. draft-ietf-nfsv4-migration-issues-07.txt>.
Work in progress. Work in progress.
[RFC1813] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS [RFC1813] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
Version 3 Protocol Specification", RFC 1813, June 1995. Version 3 Protocol Specification", RFC 1813,
DOI 10.17487/RFC1813, June 1995,
<http://www.rfc-editor.org/info/rfc1813>.
[RFC5661] Shepler, S., Eisler, M., and D. Noveck, "Network File [RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
System (NFS) Version 4 Minor Version 1 Protocol", RFC "Network File System (NFS) Version 4 Minor Version 1
5661, January 2010. Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
<http://www.rfc-editor.org/info/rfc5661>.
Appendix A. Acknowledgements Appendix A. Acknowledgements
The editor and authors of this document gratefully acknowledge the The editor and authors of this document gratefully acknowledge the
contributions of Trond Myklebust of Primary Data and Robert Thurlow contributions of Trond Myklebust of Primary Data and Robert Thurlow
of Oracle. We also thank Tom Haynes of Primary Data and Spencer of Oracle. We also thank Tom Haynes of Primary Data and Spencer
Shepler of Microsoft for their guidance and suggestions. Shepler of Microsoft for their guidance and suggestions.
Special thanks go to members of the Oracle Solaris NFS team, Special thanks go to members of the Oracle Solaris NFS team,
especially Rick Mesta and James Wahlig, for their work implementing especially Rick Mesta and James Wahlig, for their work implementing
skipping to change at page 47, line 4 skipping to change at page 52, line 23
contributions of Trond Myklebust of Primary Data and Robert Thurlow contributions of Trond Myklebust of Primary Data and Robert Thurlow
of Oracle. We also thank Tom Haynes of Primary Data and Spencer of Oracle. We also thank Tom Haynes of Primary Data and Spencer
Shepler of Microsoft for their guidance and suggestions. Shepler of Microsoft for their guidance and suggestions.
Special thanks go to members of the Oracle Solaris NFS team, Special thanks go to members of the Oracle Solaris NFS team,
especially Rick Mesta and James Wahlig, for their work implementing especially Rick Mesta and James Wahlig, for their work implementing
an NFSv4.0 migration prototype and identifying many of the issues an NFSv4.0 migration prototype and identifying many of the issues
addressed here. addressed here.
Authors' Addresses Authors' Addresses
David Noveck (editor) David Noveck (editor)
Hewlett-Packard Hewlett Packard Enterprise
165 Dascomb Road 165 Dascomb Road
Andover, MA 01810 Andover, MA 01810
US US
Phone: +1 978 474 2011 Phone: +1 978 474 2011
Email: davenoveck@gmail.com Email: davenoveck@gmail.com
Piyush Shivam Piyush Shivam
Oracle Corporation Oracle Corporation
5300 Riata Park Ct. 5300 Riata Park Ct.
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