mirror of https://gitee.com/openkylin/linux.git
142 lines
5.3 KiB
ReStructuredText
142 lines
5.3 KiB
ReStructuredText
==========
|
|
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}
|