[Qemu-devel] [PATCH v16 00/14] Drop in_use from BlockDriverState and enable point-in-time snapshot exporting over NBD

[Fam Zheng <famz@redhat.com>]

This series adds for point-in-time snapshot NBD exporting based on
blockdev-backup (variant of drive-backup with existing device as target).

We get a thin point-in-time snapshot by COW mechanism of drive-backup, and
export it through built in NBD server. The steps are as below:

 1. (SHELL) qemu-img create -f qcow2 BACKUP.qcow2 <source size here>

    (Alternatively we can use -o backing_file=RUNNING-VM.img to omit explicitly
    providing the size by ourselves, but it's risky because RUNNING-VM.qcow2 is
    used r/w by guest. Whether or not setting backing file in the image file
    doesn't matter, as we are going to override the backing hd in the next
    step)

 2. (QMP) blockdev-add backing=source-drive file.driver=file file.filename=BACKUP.qcow2 id=target0 if=none driver=qcow2

    (where source-drive is the running BlockDriverState name for
    RUNNING-VM.img. This patch implements "backing=" option to override
    backing_hd for added drive)

 3. (QMP) blockdev-backup device=source-drive sync=none target=target0

    (this is the QMP command introduced by this series, which use a named
    device as target of drive-backup)

 4. (QMP) nbd-server-add device=target0

When image fleecing done:

 1. (QMP) block-job-cancel device=source-drive

 2. (HMP) drive_del target0

 3. (SHELL) rm BACKUP.qcow2

v16: Address review comments from Jeff and Markus (thanks for reviewing!)
     (A side-by-side diff of v15 -> v16: http://goo.gl/1goc6S)

    [03/14] block: Replace in_use with operation blocker
            Improve error message. (Markus)

    [05/14] block: Add bdrv_set_backing_hd()
            in bdrv_set_backing_hd:
            * Don't call bdrv_ref and bdrv_unref. (Jeff)
            * Add "bs->open_flags &= ~BDRV_O_NO_BACKING". (Jeff)
            in bdrv_open_backing_file:
            * Remove unnecessary "bs->backing_hd = NULL;". (Jeff)
            * Don't get wrong refcnt on backing_hd. (Jeff)
            in bdrv_append:
            * Remove unnessary backing_file and backing_format copy, it's taken
              care of in bdrv_set_backing_hd(). (Jeff)

    [06/14] block: Add backing_blocker in BlockDriverState
            Add call to bdrv_ref() since bdrv_set_backing_hd() doesn't do it
            now.

    [08/14] block: Support dropping active in bdrv_drop_intermediate
            Verify active, top, base are in the same backing chain. (Jeff)
            Remember to change backing file when base != NULL. (Jeff)
            
    [09/14] stream: Use bdrv_drop_intermediate and drop close_unused_images
            Drop more unnecessary code. (Jeff)

Thanks,
Fam


Fam Zheng (14):
  block: Add BlockOpType enum
  block: Introduce op_blockers to BlockDriverState
  block: Replace in_use with operation blocker
  block: Move op_blocker check from block_job_create to its caller
  block: Add bdrv_set_backing_hd()
  block: Add backing_blocker in BlockDriverState
  block: Parse "backing" option to reference existing BDS
  block: Support dropping active in bdrv_drop_intermediate
  stream: Use bdrv_drop_intermediate and drop close_unused_images
  qmp: Add command 'blockdev-backup'
  block: Allow backup on referenced named BlockDriverState
  block: Add blockdev-backup to transaction
  qemu-iotests: Test blockdev-backup in 055
  qemu-iotests: Image fleecing test case 083

 block-migration.c               |   7 +-
 block.c                         | 314 +++++++++++++++++++++++++++-------------
 block/backup.c                  |  26 ++++
 block/commit.c                  |   2 +-
 block/mirror.c                  |   1 +
 block/stream.c                  |  42 +-----
 blockdev.c                      | 122 ++++++++++++++--
 blockjob.c                      |  14 +-
 hw/block/dataplane/virtio-blk.c |  19 ++-
 include/block/block.h           |  29 +++-
 include/block/block_int.h       |   9 +-
 include/block/blockjob.h        |   3 +
 qapi-schema.json                |  50 +++++++
 qmp-commands.hx                 |  44 ++++++
 tests/qemu-iotests/055          | 275 +++++++++++++++++++++++++++++------
 tests/qemu-iotests/055.out      |   4 +-
 tests/qemu-iotests/083          |  99 +++++++++++++
 tests/qemu-iotests/083.out      |   5 +
 tests/qemu-iotests/group        |   1 +
 19 files changed, 854 insertions(+), 212 deletions(-)
 create mode 100755 tests/qemu-iotests/083
 create mode 100644 tests/qemu-iotests/083.out

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1.9.0