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Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks.
From: |
Anthony Liguori |
Subject: |
Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks. |
Date: |
Mon, 07 Dec 2009 08:53:14 -0600 |
User-agent: |
Thunderbird 2.0.0.23 (X11/20090825) |
Daniel P. Berrange wrote:
It is safe if you assume that no one else has tried to modify the disk
since you opened it, otherwise you'd be commiting changes against a
base state which no longer exists.
1) first user opens cow1.qcow, acquires F_WRLCK
2) first user opens base.qcow, acquires F_RDLCK
3) second user opens cow2.qcow, acquires F_WRLCK
4) second user opens base.qcow, acquires F_RDLCK
5) second user attempts to commit cow2.qcow to base.qcow, tries to
acquire F_WRLCK. Calling F_SETLK with F_WRLCK will drop the F_RDLCK and
upgrade to F_WRLCK.
6) F_SETLK fails because another process is holding F_RDLCK, error is
printed to user
Now assume that there is only one user and commit succeeded, then we'd
drop back down to F_RDLCK (after an fsync) which means that afterwards,
people could open up the image again.
Regards,
Anthony Liguori
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., (continued)
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Daniel P. Berrange, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Richard W.M. Jones, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Jamie Lokier, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Daniel P. Berrange, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Richard W.M. Jones, 2009/12/07
- [Qemu-devel] Re: [PATCH] Disk image shared and exclusive locks., Paolo Bonzini, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Anthony Liguori, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Daniel P. Berrange, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Anthony Liguori, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Daniel P. Berrange, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks.,
Anthony Liguori <=
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Kevin Wolf, 2009/12/08
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Richard W.M. Jones, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Richard W.M. Jones, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Jamie Lokier, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Anthony Liguori, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Richard W.M. Jones, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Anthony Liguori, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Richard W.M. Jones, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Anthony Liguori, 2009/12/07
- Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks., Kevin Wolf, 2009/12/08