linux/Documentation/filesystems/gfs2-uevents.txt
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   1                              uevents and GFS2
   2                             ==================
   3
   4During the lifetime of a GFS2 mount, a number of uevents are generated.
   5This document explains what the events are and what they are used
   6for (by gfs_controld in gfs2-utils).
   7
   8A list of GFS2 uevents
   9-----------------------
  10
  111. ADD
  12
  13The ADD event occurs at mount time. It will always be the first
  14uevent generated by the newly created filesystem. If the mount
  15is successful, an ONLINE uevent will follow.  If it is not successful
  16then a REMOVE uevent will follow.
  17
  18The ADD uevent has two environment variables: SPECTATOR=[0|1]
  19and RDONLY=[0|1] that specify the spectator status (a read-only mount
  20with no journal assigned), and read-only (with journal assigned) status
  21of the filesystem respectively.
  22
  232. ONLINE
  24
  25The ONLINE uevent is generated after a successful mount or remount. It
  26has the same environment variables as the ADD uevent. The ONLINE
  27uevent, along with the two environment variables for spectator and
  28RDONLY are a relatively recent addition (2.6.32-rc+) and will not
  29be generated by older kernels.
  30
  313. CHANGE
  32
  33The CHANGE uevent is used in two places. One is when reporting the
  34successful mount of the filesystem by the first node (FIRSTMOUNT=Done).
  35This is used as a signal by gfs_controld that it is then ok for other
  36nodes in the cluster to mount the filesystem.
  37
  38The other CHANGE uevent is used to inform of the completion
  39of journal recovery for one of the filesystems journals. It has
  40two environment variables, JID= which specifies the journal id which
  41has just been recovered, and RECOVERY=[Done|Failed] to indicate the
  42success (or otherwise) of the operation. These uevents are generated
  43for every journal recovered, whether it is during the initial mount
  44process or as the result of gfs_controld requesting a specific journal
  45recovery via the /sys/fs/gfs2/<fsname>/lock_module/recovery file.
  46
  47Because the CHANGE uevent was used (in early versions of gfs_controld)
  48without checking the environment variables to discover the state, we
  49cannot add any more functions to it without running the risk of
  50someone using an older version of the user tools and breaking their
  51cluster. For this reason the ONLINE uevent was used when adding a new
  52uevent for a successful mount or remount.
  53
  544. OFFLINE
  55
  56The OFFLINE uevent is only generated due to filesystem errors and is used
  57as part of the "withdraw" mechanism. Currently this doesn't give any
  58information about what the error is, which is something that needs to
  59be fixed.
  60
  615. REMOVE
  62
  63The REMOVE uevent is generated at the end of an unsuccessful mount
  64or at the end of a umount of the filesystem. All REMOVE uevents will
  65have been preceded by at least an ADD uevent for the same filesystem,
  66and unlike the other uevents is generated automatically by the kernel's
  67kobject subsystem.
  68
  69
  70Information common to all GFS2 uevents (uevent environment variables)
  71----------------------------------------------------------------------
  72
  731. LOCKTABLE=
  74
  75The LOCKTABLE is a string, as supplied on the mount command
  76line (locktable=) or via fstab. It is used as a filesystem label
  77as well as providing the information for a lock_dlm mount to be
  78able to join the cluster.
  79
  802. LOCKPROTO=
  81
  82The LOCKPROTO is a string, and its value depends on what is set
  83on the mount command line, or via fstab. It will be either
  84lock_nolock or lock_dlm. In the future other lock managers
  85may be supported.
  86
  873. JOURNALID=
  88
  89If a journal is in use by the filesystem (journals are not
  90assigned for spectator mounts) then this will give the
  91numeric journal id in all GFS2 uevents.
  92
  934. UUID=
  94
  95With recent versions of gfs2-utils, mkfs.gfs2 writes a UUID
  96into the filesystem superblock. If it exists, this will
  97be included in every uevent relating to the filesystem.
  98
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