Re: [Qemu-devel] [PATCH for-2.7 v2 00/17] block: Lock images when opening

["Denis V. Lunev" <den@openvz.org>]

On 04/15/2016 06:27 AM, Fam Zheng wrote:
> v2: Lock byte 1 in the image itself, no lock file. [Daniel]
>      Fix migration (image are not locked in bdrv_open_common if
>      BDRV_O_INACTIVE). [Denis]
>      Simplify test case fixes because of the above.
>      Add lock for RBD.
>      Add "-L" option in "qemu-img" and "qemu-nbd" too. [Denis]
>      Add test case for image locking.
>
> 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. The difference is that libvirt locks byte 0,
> we lock byte 1.  Read only openings are mapped to shared locks.
>
> The alternative locking API, 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.
>
> Fam Zheng (17):
>    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
>    raw-posix: Implement .bdrv_lockf
>    gluster: Implement .bdrv_lockf
>    rbd: Implement image locking
>    qemu-io: Add "-L" option for BDRV_O_NO_LOCK
>    qemu-img: Add "-L" option to sub commands
>    qemu-img: Update documentation of "-L" option
>    qemu-nbd: Add "--no-lock/-L" option
>    qemu-iotests: 140: Disable image lock for qemu-io access
>    qemu-iotests: 046: Move version detection out from verify_io
>    qemu-iotests: Wait for QEMU processes before checking image in 091
>    qemu-iotests: Disable image lock when checking test image
>    block: Turn on image locking by default
>    qemu-iotests: Add test case 152 for image locking
>
>   block.c                    |  42 ++++++++
>   block/gluster.c            |  30 ++++++
>   block/raw-posix.c          |  35 +++++++
>   block/rbd.c                |  25 +++++
>   blockdev.c                 |   8 ++
>   include/block/block.h      |   1 +
>   include/block/block_int.h  |  12 +++
>   qapi/block-core.json       |   6 +-
>   qemu-img-cmds.hx           |  44 ++++-----
>   qemu-img.c                 |  90 +++++++++++++----
>   qemu-img.texi              |   3 +
>   qemu-io.c                  |  22 ++++-
>   qemu-nbd.c                 |   6 +-
>   qemu-nbd.texi              |   2 +
>   tests/qemu-iotests/030     |   2 +-
>   tests/qemu-iotests/046     |  22 +++--
>   tests/qemu-iotests/091     |   3 +
>   tests/qemu-iotests/091.out |   1 +
>   tests/qemu-iotests/140     |   2 +-
>   tests/qemu-iotests/152     | 106 ++++++++++++++++++++
>   tests/qemu-iotests/152.out | 237 +++++++++++++++++++++++++++++++++++++++++++++
>   tests/qemu-iotests/group   |   1 +
>   22 files changed, 645 insertions(+), 55 deletions(-)
>   create mode 100755 tests/qemu-iotests/152
>   create mode 100644 tests/qemu-iotests/152.out
>
done for now...