[Qemu-devel] [PATCH v6 00/10] Drop in_use from BlockDriverState and enable point-in-time snapshot exporting over NBD

[Fam Zheng]

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 ide0-hd0 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-complete device=ide0-hd0

 2. (HMP) drive_del target0

 3. (SHELL) rm BACKUP.qcow2

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


Fam Zheng (10):
  qapi: Add BlockOperationType enum
  block: Introduce op_blockers to 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
  block: Replace in_use with operation blocker
  block: Pass error in bdrv_snapshot_create
  block: Add checks of blocker in block operations
  qmp: add command 'blockdev-backup'
  block: Allow backup on referenced named BlockDriverState

 block-migration.c               |   8 +-
 block.c                         | 348 +++++++++++++++++++++++++---------------
 block/backup.c                  |  21 +++
 block/commit.c                  |   1 +
 block/mirror.c                  |   2 +-
 block/snapshot.c                |  16 +-
 block/stream.c                  |  28 +---
 blockdev.c                      |  86 ++++++++--
 blockjob.c                      |  12 +-
 hw/block/dataplane/virtio-blk.c |  16 +-
 include/block/block.h           |  11 +-
 include/block/block_int.h       |   9 +-
 include/block/blockjob.h        |   3 +
 include/block/snapshot.h        |   3 +-
 qapi-schema.json                |  98 +++++++++++
 qemu-img.c                      |   2 +-
 qmp-commands.hx                 |  44 +++++
 savevm.c                        |   2 +-
 18 files changed, 520 insertions(+), 190 deletions(-)

-- 
1.8.4.2