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Re: [Qemu-devel] [PATCH v6 00/10] Drop in_use from BlockDriverState and

From: Fam Zheng
Subject: Re: [Qemu-devel] [PATCH v6 00/10] Drop in_use from BlockDriverState and enable point-in-time snapshot exporting over NBD
Date: Wed, 11 Dec 2013 10:46:49 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.1

On 2013年11月28日 16:39, 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

  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.


Based on the size of change, this series needs some more review before merging. And I'd like to know if there is any concern or objection with op_blocker introduced here. I would like to base my next series (incremental backup with dirty bitmap) on it.

Any more reviews/comments?



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