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Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening |
Date: |
Thu, 14 Apr 2016 10:36:27 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, 04/13 13:18, Denis V. Lunev wrote:
> On 04/13/2016 12:09 PM, Fam Zheng wrote:
> >Too many troubles have been caused by two processes writing to the same image
> >unexpectedly. This series introduces automatical image locking into QEMU to
> >avoid such tragedy. With this, the user won't be able to open the image from
> >two processes (e.g. using qemu-img when the image is attached to the guest).
> >
> >Underneath is the fcntl syscall that locks the local file, similar to what is
> >already used in libvirt virtlockd. Also because of that, we cannot directly
> >apply fcntl lock on the image file itself, instead we open and lock
> >"/var/tmp/.qemu-$sha1.lock", where $sha1 is derived from the image's full
> >path
> >as in realpath(3). This mechanism should be equally useful for the single
> >host
> >case, and it doesn't conflict with virtlockd when managed by libvirt.
> >
> >The alternative file locking API on Linux, flock(2), cannot protect host NFS
> >mount points, so it's not used.
> >
> >Gluster locking is also implemented wrapping glfs_posix_lock in patch 6. It's
> >only lightly tested.
> >
> >All other drivers that don't implement .bdrv_lockf are always permissive and
> >does no checking.
> >
> >In the future, the intention is that image format drivers that introduce
> >locking mechanisms could also fit into this API.
> >
> >The first 6 patches define the internal and external interfaces, and
> >implement
> >the image locking.
> >
> >Patch 7 adds an option in qemu-io to allow disabling the lock, for testing
> >purpose.
> >
> >Patches 8 - 14 fixes the potential failures of test cases where multiple
> >processes may open the image concurrently.
> >
> >Finally the default behavior is switched to on in patch 15.
> >
> >Fam Zheng (15):
> > block: Add BDRV_O_NO_LOCK
> > qapi: Add lock-image in blockdev-add options
> > blockdev: Add and parse "lock-image" option for block devices
> > block: Introduce image file locking interface
> > raw-posix: Implement .bdrv_lockf
> > gluster: Implement .bdrv_lockf
> > qemu-io: Add "-L" option for BDRV_O_NO_LOCK
> > qemu-iotests: 140: Disable image lock for qemu-io access
> > qemu-iotests: 046: Move version detection out from verify_io
> > qemu-iotests: Fix lock-image for shared disk in test case 091
> > qemu-iotests: Disable image lock when checking test image
> > qemu-iotests: 051: Disable image lock in the command line
> > ahci-test: Specify "lock-image=off" in CLI
> > ide-test: Specify "lock-image=off" in command lines
> > block: Turn on image locking by default
> >
> > block.c | 25 +++++++++++
> > block/gluster.c | 34 +++++++++++++++
> > block/raw-posix.c | 97
> > +++++++++++++++++++++++++++++++++++++++++++
> > blockdev.c | 8 ++++
> > include/block/block.h | 9 ++++
> > include/block/block_int.h | 5 +++
> > qapi/block-core.json | 6 ++-
> > qemu-io.c | 22 +++++++++-
> > tests/ahci-test.c | 16 +++++--
> > tests/ide-test.c | 5 ++-
> > tests/qemu-iotests/030 | 2 +-
> > tests/qemu-iotests/046 | 22 +++++-----
> > tests/qemu-iotests/051 | 2 +-
> > tests/qemu-iotests/051.out | 10 ++---
> > tests/qemu-iotests/051.pc.out | 10 ++---
> > tests/qemu-iotests/091 | 4 +-
> > tests/qemu-iotests/140 | 2 +-
> > 17 files changed, 245 insertions(+), 34 deletions(-)
> >
> First of all, I like the approach as we have discussed :) Then,
> in general, I support Daniel with the point that
> the locking should be done on the image file
> directly.
>
> Also, it looks like this will break migration with the shared storage.
> For me it seems that we will have lock the image from both ends
There should already be state handling logic between source and destinition
ends, I'll take a look and see if we can add lock/unlock calls there to keep it
working.
Fam
- [Qemu-devel] [PATCH for-2.7 09/15] qemu-iotests: 046: Move version detection out from verify_io, (continued)
- [Qemu-devel] [PATCH for-2.7 09/15] qemu-iotests: 046: Move version detection out from verify_io, Fam Zheng, 2016/04/13
- [Qemu-devel] [PATCH for-2.7 11/15] qemu-iotests: Disable image lock when checking test image, Fam Zheng, 2016/04/13
- [Qemu-devel] [PATCH for-2.7 10/15] qemu-iotests: Fix lock-image for shared disk in test case 091, Fam Zheng, 2016/04/13
- [Qemu-devel] [PATCH for-2.7 13/15] ahci-test: Specify "lock-image=off" in CLI, Fam Zheng, 2016/04/13
- [Qemu-devel] [PATCH for-2.7 15/15] block: Turn on image locking by default, Fam Zheng, 2016/04/13
- [Qemu-devel] [PATCH for-2.7 12/15] qemu-iotests: 051: Disable image lock in the command line, Fam Zheng, 2016/04/13
- [Qemu-devel] [PATCH for-2.7 14/15] ide-test: Specify "lock-image=off" in command lines, Fam Zheng, 2016/04/13
- Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening, Daniel P. Berrange, 2016/04/13
- Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening, Denis V. Lunev, 2016/04/13
- Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening,
Fam Zheng <=
- Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening, Denis V. Lunev, 2016/04/14
- Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening, Fam Zheng, 2016/04/14
- Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening, Denis V. Lunev, 2016/04/14
- Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening, Fam Zheng, 2016/04/14
- Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening, Denis V. Lunev, 2016/04/14
Re: [Qemu-devel] [PATCH for-2.7 00/15] block: Lock images when opening, Richard W.M. Jones, 2016/04/17