0aa8744584
This will be essential reading for anybody who wants to understand how GFS2 interacts with the userland gfs_controld, and the details of recovery. Signed-off-by: Steven Whitehouse <swhiteho@redhat.com> Signed-off-by: Bob Peterson <rpeterso@redhat.com>
100 lines
3.7 KiB
Text
100 lines
3.7 KiB
Text
uevents and GFS2
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==================
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During the lifetime of a GFS2 mount, a number of uevents are generated.
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This document explains what the events are and what they are used
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for (by gfs_controld in gfs2-utils).
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A list of GFS2 uevents
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-----------------------
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1. ADD
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The ADD event occurs at mount time. It will always be the first
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uevent generated by the newly created filesystem. If the mount
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is successful, an ONLINE uevent will follow. If it is not successful
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then a REMOVE uevent will follow.
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The ADD uevent has two environment variables: SPECTATOR=[0|1]
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and RDONLY=[0|1] that specify the spectator status (a read-only mount
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with no journal assigned), and read-only (with journal assigned) status
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of the filesystem respectively.
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2. ONLINE
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The ONLINE uevent is generated after a successful mount or remount. It
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has the same environment variables as the ADD uevent. The ONLINE
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uevent, along with the two environment variables for spectator and
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RDONLY are a relatively recent addition (2.6.32-rc+) and will not
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be generated by older kernels.
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3. CHANGE
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The CHANGE uevent is used in two places. One is when reporting the
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successful mount of the filesystem by the first node (FIRSTMOUNT=Done).
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This is used as a signal by gfs_controld that it is then ok for other
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nodes in the cluster to mount the filesystem.
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The other CHANGE uevent is used to inform of the completion
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of journal recovery for one of the filesystems journals. It has
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two environment variables, JID= which specifies the journal id which
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has just been recovered, and RECOVERY=[Done|Failed] to indicate the
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success (or otherwise) of the operation. These uevents are generated
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for every journal recovered, whether it is during the initial mount
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process or as the result of gfs_controld requesting a specific journal
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recovery via the /sys/fs/gfs2/<fsname>/lock_module/recovery file.
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Because the CHANGE uevent was used (in early versions of gfs_controld)
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without checking the environment variables to discover the state, we
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cannot add any more functions to it without running the risk of
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someone using an older version of the user tools and breaking their
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cluster. For this reason the ONLINE uevent was used when adding a new
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uevent for a successful mount or remount.
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4. OFFLINE
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The OFFLINE uevent is only generated due to filesystem errors and is used
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as part of the "withdraw" mechanism. Currently this doesn't give any
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information about what the error is, which is something that needs to
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be fixed.
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5. REMOVE
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The REMOVE uevent is generated at the end of an unsuccessful mount
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or at the end of a umount of the filesystem. All REMOVE uevents will
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have been preceeded by at least an ADD uevent for the same fileystem,
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and unlike the other uevents is generated automatically by the kernel's
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kobject subsystem.
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Information common to all GFS2 uevents (uevent environment variables)
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----------------------------------------------------------------------
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1. LOCKTABLE=
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The LOCKTABLE is a string, as supplied on the mount command
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line (locktable=) or via fstab. It is used as a filesystem label
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as well as providing the information for a lock_dlm mount to be
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able to join the cluster.
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2. LOCKPROTO=
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The LOCKPROTO is a string, and its value depends on what is set
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on the mount command line, or via fstab. It will be either
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lock_nolock or lock_dlm. In the future other lock managers
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may be supported.
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3. JOURNALID=
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If a journal is in use by the filesystem (journals are not
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assigned for spectator mounts) then this will give the
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numeric journal id in all GFS2 uevents.
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4. UUID=
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With recent versions of gfs2-utils, mkfs.gfs2 writes a UUID
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into the filesystem superblock. If it exists, this will
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be included in every uevent relating to the filesystem.
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