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

From: Fam Zheng
Subject: [Qemu-devel] [PATCH for-2.7 v2 00/17] block: Lock images when opening
Date: Fri, 15 Apr 2016 11:27:50 +0800

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


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