On 2013年12月13日 10:40, Ian Main wrote:
On Thu, Dec 12, 2013 at 04:23:36PM +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-complete device=source-drive
If you do another revision, this should be block-job-cancel.

OK, thanks for reminding.

Fam


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