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Previously, a command sent lvmetad new VG metadata in vg_commit().
In vg_commit(), devices are suspended, so any memory allocation
done by the command while sending to lvmetad, or by lvmetad while
updating its cache could deadlock if memory reclaim was triggered.
Now lvmetad is updated in unlock_vg(), after devices are resumed.
The new method for updating VG metadata in lvmetad is in two phases:
1. In vg_write(), before devices are suspended, the command sends
lvmetad a short message ("set_vg_info") telling it what the new
VG seqno will be. lvmetad sees that the seqno is newer than
the seqno of its cached VG, so it sets the INVALID flag for the
cached VG. If sending the message to lvmetad fails, the command
fails before the metadata is committed and the change is not made.
If sending the message succeeds, vg_commit() is called.
2. In unlock_vg(), after devices are resumed, the command sends
lvmetad the standard vg_update message with the new metadata.
lvmetad sees that the seqno in the new metadata matches the
seqno it saved from set_vg_info, and knows it has the latest
copy, so it clears the INVALID flag for the cached VG.
If a command fails between 1 and 2 (after committing the VG on disk,
but before sending lvmetad the new metadata), the cached VG retains
the INVALID flag in lvmetad. A subsequent command will read the
cached VG from lvmetad, see the INVALID flag, ignore the cached
copy, read the VG from disk instead, update the lvmetad copy
with the latest copy from disk, (this clears the INVALID flag
in lvmetad), and use the correct VG metadata for the command.
(This INVALID mechanism already existed for use by lvmlockd.)
This tree contains the LVM2 and device-mapper tools and libraries. For more information about LVM2 read the changelog in the WHATS_NEW file. Installation instructions are in INSTALL. There is no warranty - see COPYING and COPYING.LIB. Tarballs are available from: ftp://sources.redhat.com/pub/lvm2/ The source code is stored in git: http://git.fedorahosted.org/git/lvm2.git git clone git://git.fedorahosted.org/git/lvm2.git Mailing list for general discussion related to LVM2: linux-lvm@redhat.com Subscribe from https://www.redhat.com/mailman/listinfo/linux-lvm Mailing lists for LVM2 development, patches and commits: lvm-devel@redhat.com Subscribe from https://www.redhat.com/mailman/listinfo/lvm-devel lvm2-commits@lists.fedorahosted.org (Read-only archive of commits) Subscribe from https://fedorahosted.org/mailman/listinfo/lvm2-commits Mailing list for device-mapper development, including kernel patches and multipath-tools: dm-devel@redhat.com Subscribe from https://www.redhat.com/mailman/listinfo/dm-devel The source code repository used until 7th June 2012 is accessible here: http://sources.redhat.com/cgi-bin/cvsweb.cgi/LVM2/?cvsroot=lvm2.