diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/gfs2-uevents.txt | 100 | ||||
| -rw-r--r-- | Documentation/filesystems/nfs.txt | 98 | ||||
| -rw-r--r-- | Documentation/filesystems/seq_file.txt | 2 |
3 files changed, 199 insertions, 1 deletions
diff --git a/Documentation/filesystems/gfs2-uevents.txt b/Documentation/filesystems/gfs2-uevents.txt new file mode 100644 index 00000000000..fd966dc9979 --- /dev/null +++ b/Documentation/filesystems/gfs2-uevents.txt @@ -0,0 +1,100 @@ + uevents and GFS2 + ================== + +During the lifetime of a GFS2 mount, a number of uevents are generated. +This document explains what the events are and what they are used +for (by gfs_controld in gfs2-utils). + +A list of GFS2 uevents +----------------------- + +1. ADD + +The ADD event occurs at mount time. It will always be the first +uevent generated by the newly created filesystem. If the mount +is successful, an ONLINE uevent will follow. If it is not successful +then a REMOVE uevent will follow. + +The ADD uevent has two environment variables: SPECTATOR=[0|1] +and RDONLY=[0|1] that specify the spectator status (a read-only mount +with no journal assigned), and read-only (with journal assigned) status +of the filesystem respectively. + +2. ONLINE + +The ONLINE uevent is generated after a successful mount or remount. It +has the same environment variables as the ADD uevent. The ONLINE +uevent, along with the two environment variables for spectator and +RDONLY are a relatively recent addition (2.6.32-rc+) and will not +be generated by older kernels. + +3. CHANGE + +The CHANGE uevent is used in two places. One is when reporting the +successful mount of the filesystem by the first node (FIRSTMOUNT=Done). +This is used as a signal by gfs_controld that it is then ok for other +nodes in the cluster to mount the filesystem. + +The other CHANGE uevent is used to inform of the completion +of journal recovery for one of the filesystems journals. It has +two environment variables, JID= which specifies the journal id which +has just been recovered, and RECOVERY=[Done|Failed] to indicate the +success (or otherwise) of the operation. These uevents are generated +for every journal recovered, whether it is during the initial mount +process or as the result of gfs_controld requesting a specific journal +recovery via the /sys/fs/gfs2/<fsname>/lock_module/recovery file. + +Because the CHANGE uevent was used (in early versions of gfs_controld) +without checking the environment variables to discover the state, we +cannot add any more functions to it without running the risk of +someone using an older version of the user tools and breaking their +cluster. For this reason the ONLINE uevent was used when adding a new +uevent for a successful mount or remount. + +4. OFFLINE + +The OFFLINE uevent is only generated due to filesystem errors and is used +as part of the "withdraw" mechanism. Currently this doesn't give any +information about what the error is, which is something that needs to +be fixed. + +5. REMOVE + +The REMOVE uevent is generated at the end of an unsuccessful mount +or at the end of a umount of the filesystem. All REMOVE uevents will +have been preceeded by at least an ADD uevent for the same fileystem, +and unlike the other uevents is generated automatically by the kernel's +kobject subsystem. + + +Information common to all GFS2 uevents (uevent environment variables) +---------------------------------------------------------------------- + +1. LOCKTABLE= + +The LOCKTABLE is a string, as supplied on the mount command +line (locktable=) or via fstab. It is used as a filesystem label +as well as providing the information for a lock_dlm mount to be +able to join the cluster. + +2. LOCKPROTO= + +The LOCKPROTO is a string, and its value depends on what is set +on the mount command line, or via fstab. It will be either +lock_nolock or lock_dlm. In the future other lock managers +may be supported. + +3. JOURNALID= + +If a journal is in use by the filesystem (journals are not +assigned for spectator mounts) then this will give the +numeric journal id in all GFS2 uevents. + +4. UUID= + +With recent versions of gfs2-utils, mkfs.gfs2 writes a UUID +into the filesystem superblock. If it exists, this will +be included in every uevent relating to the filesystem. + + + diff --git a/Documentation/filesystems/nfs.txt b/Documentation/filesystems/nfs.txt new file mode 100644 index 00000000000..f50f26ce6cd --- /dev/null +++ b/Documentation/filesystems/nfs.txt @@ -0,0 +1,98 @@ + +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 +upcall interfaces that are used in order to provide the NFS client with +some of the information that it requires in order to fully comply with +the NFS spec. + +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} + diff --git a/Documentation/filesystems/seq_file.txt b/Documentation/filesystems/seq_file.txt index b843743aa0b..0d15ebccf5b 100644 --- a/Documentation/filesystems/seq_file.txt +++ b/Documentation/filesystems/seq_file.txt @@ -46,7 +46,7 @@ better to do. The file is seekable, in that one can do something like the following: dd if=/proc/sequence of=out1 count=1 - dd if=/proc/sequence skip=1 out=out2 count=1 + dd if=/proc/sequence skip=1 of=out2 count=1 Then concatenate the output files out1 and out2 and get the right result. Yes, it is a thoroughly useless module, but the point is to show |