[Qemu-devel] [PATCH v8 00/12] 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

v8: Address comments from Markus, Kevin and Ian. Thanks for the review!

    Cover letter fixed "block-job-cancel". (Ian)

    Dropped "[v7 07/10] block: Pass error in bdrv_snapshot_create". (Markus)
    Dropped "[v7 08/10] block: Add checks of blocker in block operations". (Markus)
    They are neither necessary for this series nor significant improvements.

    [01/10] qapi: Add BlockOperationType enum
            Since 2.0. (Kevin, Markus)
    [02/10] block: Introduce op_blockers to BlockDriverState
            Commit message reword. (Markus)
            Move bdrv_op_blocker_is_empty() here.
    [03/10] block: Replace in_use with operation blocker
            Moved to the front of series.
            Reword commit message. (Markus)
            Move memcpy in bdrv_move_feature_fields() into 02/10. (Markus)
            Don't drop in_use asserts, convert them. (Markus)
            Drop unused local_err. (Markus)
            Simplify bdrv_op_blocker_is_empty(). (Markus)
            Fix error message for do_drive_del() and dataplane. (Markus)
            Remember to error_free for dataplane op blocker. (Markus)
            Drop whitespace change. (Markus)
            Mechanical convert of in_use for block_job_create().
    [04/10] block: Add bdrv_set_backing_hd()
            New. Separate the common part for setting backing_hd.
    [05/10] block: Add backing_blocker in BlockDriverState
            New.
    [06/10] block: Parse "backing" option to reference existing BDS
            Make use of 04/10.
            We need to delete "backing" from qdict, otherwise QMP complains
            with an supported option, not dropping it. (Markus)
            Move error_free(bs->backing_blocker) in bdrv_close(). (Markus)
            Reword comment for backing_blocker. (Markus)
            03/10 retained the logic of in_use assert, this is no longer true
            since backing_hd has a blocker on it. So drop it. (Markus)
    [07/10] block: Support dropping active in bdrv_drop_intermediate
            Make use of 04/10. (Kevin)
            Pass NULL, NULL instead of empty string to bdrv_change_backing_file. (Kevin)
    [08/10] stream: Use bdrv_drop_intermediate and drop close_unused_images
    [09/10] qmp: Add command 'blockdev-backup'
            Since 1.8 -> Since 2.0.
    [10/10] block: Allow backup on referenced named BlockDriverState

v7: Fix typo in cover letter "ide0-hd0". (Markus)
    Rebase to current qemu.git. (Resolved a few trivial contextual conflict)

v6: Address Paolo's comments, (except for bitmask):
    - Add blocker for all backing_hd references, a relatively big change, some
      patches are reordered.
    - Introduce a few other necessary patches.
    - Move two snapshot checks into bdrv_snapshot_*.

    The interface is unchanged.

Fam Zheng (12):
  blkdebug: Use QLIST_FOREACH_SAFE to resume IO
  qapi: Add BlockOperationType 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-migration.c               |   7 +-
 block.c                         | 291 ++++++++++++++++++++++++++--------------
 block/backup.c                  |  21 +++
 block/blkdebug.c                |   8 +-
 block/commit.c                  |   1 +
 block/stream.c                  |  28 +---
 blockdev.c                      |  70 ++++++++--
 blockjob.c                      |  14 +-
 hw/block/dataplane/virtio-blk.c |  18 ++-
 include/block/block.h           |  10 +-
 include/block/block_int.h       |   9 +-
 include/block/blockjob.h        |   3 +
 qapi-schema.json                |  99 ++++++++++++++
 qmp-commands.hx                 |  44 ++++++
 14 files changed, 465 insertions(+), 158 deletions(-)

-- 
1.8.5.1