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[Qemu-devel] [PATCH VERSION 3] Disk image exclusive and shared locks.


From: Richard W.M. Jones
Subject: [Qemu-devel] [PATCH VERSION 3] Disk image exclusive and shared locks.
Date: Tue, 15 Dec 2009 16:42:38 +0000
User-agent: Mutt/1.5.18 (2008-05-17)

This is v3 of the lock patch, previously discussed here:

http://lists.gnu.org/archive/html/qemu-devel/2009-12/threads.html#00461

In this version I've reverted back to the simpler interface.  There is
now only one "lock" option, which can be lock=exclusive|shared|none.

At Kevin Wolf's suggestion,
lock=exclusive|shared => all backing disks are locked shared
lock=none => no locks are acquired on any front or back disks

In order to mitigate the problem with locks during live migration,
I've added a lock command to the monitor, which currently allows you
to acquire (but not revoke) a lock.  (Revocation could be added fairly
easily too.)  This should allow the management tool to start the qemu
destination process without locking, and lock it once migration is
complete.

To keep the implementation very simple, the "commit" doesn't try to
acquire any extra locks.  The "commit" command should probably never
be used when a backing file could be shared.

In general I've attempted to keep the patch simple, but with room for
future extension.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://et.redhat.com/~rjones/virt-top

Attachment: 0001-Disk-image-exclusive-and-shared-locks.patch
Description: Text document


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