Re: [Qemu-devel] [PATCH v10 00/11] Drop in_use from BlockDriverState and enable point-in-time snapshot exporting over NBD

[Fam Zheng <famz@redhat.com>]

On 2014年01月08日 11:42, Fam Zheng wrote:
> 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 -> v10: Rebased to qemu.git. Address Stefan's comments:
>
>      [01/11] block: Add BlockOpType enum
>              Change enum definition as internal.
>
>      [05/11] block: Add bdrv_set_backing_hd()
>              Set bs->backing_file and bs->backing_format.
>
>      [06/11] block: Add backing_blocker in BlockDriverState
>              Reuse bdrv_set_backing_hd().
>
>      [07/11] block: Parse "backing" option to reference existing BDS
>              Fix use-after-free.
>              Check for "backing=" and "backing.file=" conflict.
>              Remove unintended bdrv_swap hunks.

Actually it is not unintended, this breaks qemu-iotests 040. The asserts 
have to be removed to allow block commit.

Will respin, sorry for posting three revisions in a row.

Fam

>
>      [08/11] block: Support dropping active in bdrv_drop_intermediate
>              Fix function comment.
>
>      [09/11] stream: Use bdrv_drop_intermediate and drop close_unused_images
>
>
> Fam Zheng (11):
>    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-migration.c               |   7 +-
>   block.c                         | 306 +++++++++++++++++++++++++++-------------
>   block/backup.c                  |  21 +++
>   block/commit.c                  |   1 +
>   block/stream.c                  |  28 +---
>   blockdev.c                      |  70 +++++++--
>   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                |  49 +++++++
>   qmp-commands.hx                 |  44 ++++++
>   13 files changed, 446 insertions(+), 154 deletions(-)
>