Re: [Qemu-devel] [PATCH v12 00/11] Drop in_use from BlockDriverState and enable point-in-time snapshot exporting over NBD

[Stefan Hajnoczi <stefanha@gmail.com>]

On Mon, Jan 27, 2014 at 11:48:06AM +0800, 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
> 
> v11 -> v12: Rebase to qemu.git.
>      Call bdrv_refresh_limits() in bdrv_set_backing_hd().
> 
> v8 -> v11: Rebased to qemu.git. Address Stefan's comments:
>     (sorry for sending 3 revisions in a day)
> 
>     [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
>             Update commit message about bdrv_swap assertion removal.
>             Fix use-after-free.
>             Check for "backing=" and "backing.file=" conflict.
> 
>     [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                         | 310 ++++++++++++++++++++++++++--------------
>  block/backup.c                  |  21 +++
>  block/commit.c                  |   1 +
>  block/stream.c                  |  30 +---
>  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(+), 160 deletions(-)

I had only one comment on the code, see my reply.  But we need tests in
order to merge this.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>