Documentation: convert nfs.txt to ReST

This patch converts nfs.txt to RST. It also moves it to admin-guide.
The reason for moving it is because this document contains information
useful for system administrators, as noted on the following paragraph:

'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'.

Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Link: https://lore.kernel.org/r/cb9f2da2f2f6dd432b4cf9e05f79f74f4d54b6ab.1578697871.git.dwlsalmeida@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 0 insertions, 136 deletions

diff --git a/Documentation/filesystems/nfs/nfs.txt b/Documentation/filesystems/nfs/nfs.txt
deleted file mode 100644
index f2571c8bef74..000000000000
--- a/Documentation/filesystems/nfs/nfs.txt
+++ /dev/null
@@ -1,136 +0,0 @@
-
-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}
-