Re: [Qemu-devel] [PATCH 0/3] block: block-backup live backup command

[Eric Blake]

On 04/23/2013 10:25 AM, Stefan Hajnoczi wrote:
> This series adds a new QMP command, block-backup, which takes a point-in-time
> snapshot of a block device.  The snapshot is copied out to a target block
> device.  A simple example is:
> 
>   block-backup device=virtio0 format=qcow2 target=backup-20130401.qcow2

> What's next for block-backup?
> -----------------------------
> The following enhancements are left for future patches:
> 
> 1. QMP 'transaction' support.  It is handy to atomically snapshot multiple
>    block devices.  We need qmp_transaction() support for this.  Wenchao Xia is
>    currently making qmp_transaction() extensible so new action types, like
>    block-backup, can be added.
> 
> 2. Sync modes like drive-mirror (top, full, none).  This makes it possible to
>    preserve the backing file chain.

Based on today's phone call, it sounds like this would mean adding
optional parameters to the QMP command.  We already did that for
drive-mirror (1.4 has more parameters than 1.3), but without a way to
introspect when those parameters are available, the new parameters
aren't quite as useful.  So we don't repeat that mistake, we need to
decide whether this should still go into 1.5 with a plan of adding
parameters for 1.6, or whether we should add a counterpart query-*
command that makes it easy to determine how much of block-backup is
supported, or [your suggestion here]....

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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