--- /dev/null
+==========
+NFS Client
+==========
+
+The NFS client
+==============
+
+The NFS version 2 protocol was first documented in RFC1094 (March 1989).
+Since then two more major releases of NFS have been published, with NFSv3
+being documented in RFC1813 (June 1995), and NFSv4 in RFC3530 (April
+2003).
+
+The Linux NFS client currently supports all the above published versions,
+and work is in progress on adding support for minor version 1 of the NFSv4
+protocol.
+
+The purpose of this document is to provide information on some of the
+special features of the NFS client that can be configured by system
+administrators.
+
+
+The nfs4_unique_id parameter
+============================
+
+NFSv4 requires clients to identify themselves to servers with a unique
+string. File open and lock state shared between one client and one server
+is associated with this identity. To support robust NFSv4 state recovery
+and transparent state migration, this identity string must not change
+across client reboots.
+
+Without any other intervention, the Linux client uses a string that contains
+the local system's node name. System administrators, however, often do not
+take care to ensure that node names are fully qualified and do not change
+over the lifetime of a client system. Node names can have other
+administrative requirements that require particular behavior that does not
+work well as part of an nfs_client_id4 string.
+
+The nfs.nfs4_unique_id boot parameter specifies a unique string that can be
+used instead of a system's node name when an NFS client identifies itself to
+a server. Thus, if the system's node name is not unique, or it changes, its
+nfs.nfs4_unique_id stays the same, preventing collision with other clients
+or loss of state during NFS reboot recovery or transparent state migration.
+
+The nfs.nfs4_unique_id string is typically a UUID, though it can contain
+anything that is believed to be unique across all NFS clients. An
+nfs4_unique_id string should be chosen when a client system is installed,
+just as a system's root file system gets a fresh UUID in its label at
+install time.
+
+The string should remain fixed for the lifetime of the client. It can be
+changed safely if care is taken that the client shuts down cleanly and all
+outstanding NFSv4 state has expired, to prevent loss of NFSv4 state.
+
+This string can be stored in an NFS client's grub.conf, or it can be provided
+via a net boot facility such as PXE. It may also be specified as an nfs.ko
+module parameter. Specifying a uniquifier string is not support for NFS
+clients running in containers.
+
+
+The DNS resolver
+================
+
+NFSv4 allows for one server to refer the NFS client to data that has been
+migrated onto another server by means of the special "fs_locations"
+attribute. See `RFC3530 Section 6: Filesystem Migration and Replication`_ and
+`Implementation Guide for Referrals in NFSv4`_.
+
+.. _RFC3530 Section 6\: Filesystem Migration and Replication: http://tools.ietf.org/html/rfc3530#section-6
+.. _Implementation Guide for Referrals in NFSv4: http://tools.ietf.org/html/draft-ietf-nfsv4-referrals-00
+
+The fs_locations information can take the form of either an ip address and
+a path, or a DNS hostname and a path. The latter requires the NFS client to
+do a DNS lookup in order to mount the new volume, and hence the need for an
+upcall to allow userland to provide this service.
+
+Assuming that the user has the 'rpc_pipefs' filesystem mounted in the usual
+/var/lib/nfs/rpc_pipefs, the upcall consists of the following steps:
+
+ (1) The process checks the dns_resolve cache to see if it contains a
+ valid entry. If so, it returns that entry and exits.
+
+ (2) If no valid entry exists, the helper script '/sbin/nfs_cache_getent'
+ (may be changed using the 'nfs.cache_getent' kernel boot parameter)
+ is run, with two arguments:
+ - the cache name, "dns_resolve"
+ - the hostname to resolve
+
+ (3) After looking up the corresponding ip address, the helper script
+ writes the result into the rpc_pipefs pseudo-file
+ '/var/lib/nfs/rpc_pipefs/cache/dns_resolve/channel'
+ in the following (text) format:
+
+ "<ip address> <hostname> <ttl>\n"
+
+ Where <ip address> is in the usual IPv4 (123.456.78.90) or IPv6
+ (ffee:ddcc:bbaa:9988:7766:5544:3322:1100, ffee::1100, ...) format.
+ <hostname> is identical to the second argument of the helper
+ script, and <ttl> is the 'time to live' of this cache entry (in
+ units of seconds).
+
+ .. note::
+ If <ip address> is invalid, say the string "0", then a negative
+ entry is created, which will cause the kernel to treat the hostname
+ as having no valid DNS translation.
+
+
+
+
+A basic sample /sbin/nfs_cache_getent
+=====================================
+.. code-block:: sh
+
+ #!/bin/bash
+ #
+ ttl=600
+ #
+ cut=/usr/bin/cut
+ getent=/usr/bin/getent
+ rpc_pipefs=/var/lib/nfs/rpc_pipefs
+ #
+ die()
+ {
+ echo "Usage: $0 cache_name entry_name"
+ exit 1
+ }
+
+ [ $# -lt 2 ] && die
+ cachename="$1"
+ cache_path=${rpc_pipefs}/cache/${cachename}/channel
+
+ case "${cachename}" in
+ dns_resolve)
+ name="$2"
+ result="$(${getent} hosts ${name} | ${cut} -f1 -d\ )"
+ [ -z "${result}" ] && result="0"
+ ;;
+ *)
+ die
+ ;;
+ esac
+ echo "${result} ${name} ${ttl}" >${cache_path}
+++ /dev/null
-
-The NFS client
-==============
-
-The NFS version 2 protocol was first documented in RFC1094 (March 1989).
-Since then two more major releases of NFS have been published, with NFSv3
-being documented in RFC1813 (June 1995), and NFSv4 in RFC3530 (April
-2003).
-
-The Linux NFS client currently supports all the above published versions,
-and work is in progress on adding support for minor version 1 of the NFSv4
-protocol.
-
-The purpose of this document is to provide information on some of the
-special features of the NFS client that can be configured by system
-administrators.
-
-
-The nfs4_unique_id parameter
-============================
-
-NFSv4 requires clients to identify themselves to servers with a unique
-string. File open and lock state shared between one client and one server
-is associated with this identity. To support robust NFSv4 state recovery
-and transparent state migration, this identity string must not change
-across client reboots.
-
-Without any other intervention, the Linux client uses a string that contains
-the local system's node name. System administrators, however, often do not
-take care to ensure that node names are fully qualified and do not change
-over the lifetime of a client system. Node names can have other
-administrative requirements that require particular behavior that does not
-work well as part of an nfs_client_id4 string.
-
-The nfs.nfs4_unique_id boot parameter specifies a unique string that can be
-used instead of a system's node name when an NFS client identifies itself to
-a server. Thus, if the system's node name is not unique, or it changes, its
-nfs.nfs4_unique_id stays the same, preventing collision with other clients
-or loss of state during NFS reboot recovery or transparent state migration.
-
-The nfs.nfs4_unique_id string is typically a UUID, though it can contain
-anything that is believed to be unique across all NFS clients. An
-nfs4_unique_id string should be chosen when a client system is installed,
-just as a system's root file system gets a fresh UUID in its label at
-install time.
-
-The string should remain fixed for the lifetime of the client. It can be
-changed safely if care is taken that the client shuts down cleanly and all
-outstanding NFSv4 state has expired, to prevent loss of NFSv4 state.
-
-This string can be stored in an NFS client's grub.conf, or it can be provided
-via a net boot facility such as PXE. It may also be specified as an nfs.ko
-module parameter. Specifying a uniquifier string is not support for NFS
-clients running in containers.
-
-
-The DNS resolver
-================
-
-NFSv4 allows for one server to refer the NFS client to data that has been
-migrated onto another server by means of the special "fs_locations"
-attribute. See
- http://tools.ietf.org/html/rfc3530#section-6
-and
- http://tools.ietf.org/html/draft-ietf-nfsv4-referrals-00
-
-The fs_locations information can take the form of either an ip address and
-a path, or a DNS hostname and a path. The latter requires the NFS client to
-do a DNS lookup in order to mount the new volume, and hence the need for an
-upcall to allow userland to provide this service.
-
-Assuming that the user has the 'rpc_pipefs' filesystem mounted in the usual
-/var/lib/nfs/rpc_pipefs, the upcall consists of the following steps:
-
- (1) The process checks the dns_resolve cache to see if it contains a
- valid entry. If so, it returns that entry and exits.
-
- (2) If no valid entry exists, the helper script '/sbin/nfs_cache_getent'
- (may be changed using the 'nfs.cache_getent' kernel boot parameter)
- is run, with two arguments:
- - the cache name, "dns_resolve"
- - the hostname to resolve
-
- (3) After looking up the corresponding ip address, the helper script
- writes the result into the rpc_pipefs pseudo-file
- '/var/lib/nfs/rpc_pipefs/cache/dns_resolve/channel'
- in the following (text) format:
-
- "<ip address> <hostname> <ttl>\n"
-
- Where <ip address> is in the usual IPv4 (123.456.78.90) or IPv6
- (ffee:ddcc:bbaa:9988:7766:5544:3322:1100, ffee::1100, ...) format.
- <hostname> is identical to the second argument of the helper
- script, and <ttl> is the 'time to live' of this cache entry (in
- units of seconds).
-
- Note: If <ip address> is invalid, say the string "0", then a negative
- entry is created, which will cause the kernel to treat the hostname
- as having no valid DNS translation.
-
-
-
-
-A basic sample /sbin/nfs_cache_getent
-=====================================
-
-#!/bin/bash
-#
-ttl=600
-#
-cut=/usr/bin/cut
-getent=/usr/bin/getent
-rpc_pipefs=/var/lib/nfs/rpc_pipefs
-#
-die()
-{
- echo "Usage: $0 cache_name entry_name"
- exit 1
-}
-
-[ $# -lt 2 ] && die
-cachename="$1"
-cache_path=${rpc_pipefs}/cache/${cachename}/channel
-
-case "${cachename}" in
- dns_resolve)
- name="$2"
- result="$(${getent} hosts ${name} | ${cut} -f1 -d\ )"
- [ -z "${result}" ] && result="0"
- ;;
- *)
- die
- ;;
-esac
-echo "${result} ${name} ${ttl}" >${cache_path}
-
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