Hi all,
On Wed, 29 Aug 2007, Alexander Graf wrote:
Paul Jakma wrote:
On Mon, 27 Aug 2007, Anthony Liguori wrote:
I think this is the right level myself. Advisory locks work okay but
not all filesystems support them... I think it would do more harm than
good to have a feature like that was supposed to provide a safe-guard
but then frequently didn't work.
^^^^^^^^^^^^^^^^^^^^^^
Are you trying to say that any kind of significant portion of QEMU
users have clustered file-systems?
I think that's unlikely, and it'd be nice if QEMU by default did a
fcntl() on writeable image files to lock itself from multiple access,
that'd benefit the vast majority of users.
I'm usually running one "main" qemu instance that has read/write access
to the disk file and several others for tests that use the -snapshot
option, so I think it's very important to have an easy means of
switching this check off.
Would it make sense to take a read lock (preventing concurrent writes) on
read-only snapshot images, and a write lock on all writable files? That
should allow one to run as many instances as you want off a single
snapshot in snapshot mode, but still prevent one from (accidentally)
running a non-snapshot QEMU on the same image, or from (accidentally)
running two instances writing to the same COW file.
By removing the need to add the lock-override command line switch to qemu
in this case, it would reduce the risk of accidental image corruption by
accidentally overriding the lock.
Cheers, Chris.
--
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\ __/ / ,__(_)_ | Chris Wilson <0000 at qwirx.com> - Cambs UK |
/ (_/ ,\/ _/ /_ \ | Security/C/C++/Java/Perl/SQL/HTML Developer |
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