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Date: Tue, 14 May 2013 10:48:57 +0200
From: Stefan Hajnoczi <stefanha@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 2/3] block: add block-backup QMP command
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To: Eric Blake <eblake@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, qemu-devel@nongnu.org, Wenchao Xia <xiawenc@linux.vnet.ibm.com>, imain@redhat.com, pbonzini@redhat.com, dietmar@proxmox.com

On Fri, May 10, 2013 at 10:02:14PM -0600, Eric Blake wrote:
> On 04/29/2013 01:42 AM, Stefan Hajnoczi wrote:
> > @block-backup
> > 
> > +++ b/qapi-schema.json
> > @@ -1715,6 +1715,37 @@
> >              '*speed': 'int' } }
> >  
> >  ##
> > +# @block-backup
> > +#
> > +# Start a point-in-time copy of a block device to a new destination.  The
> > +# status of ongoing block backup operations can be checked with
> > +# query-block-jobs.  The operation can be stopped before it has completed using
> > +# the block-job-cancel command.
> 
> Still might be worth mentioning that 'query-block-jobs' will list it as
> a job of type 'backup'.

Will fix in v3.

> > +#
> > +# @device: the name of the device whose writes should be mirrored.
> > +#
> > +# @target: the target of the new image. If the file exists, or if it
> > +#          is a device, the existing file/device will be used as the new
> > +#          destination.  If it does not exist, a new file will be created.
> > +#
> > +# @format: #optional the format of the new destination, default is to
> > +#          probe if @mode is 'existing', else the format of the source
> > +#
> > +# @mode: #optional whether and how QEMU should create a new image, default is
> > +#        'absolute-paths'.
> > +#
> > +# @speed: #optional the maximum speed, in bytes per second
> > +#
> > +# Returns: nothing on success
> > +#          If @device is not a valid block device, DeviceNotFound
> > +#
> > +# Since 1.6
> > +##
> > +{ 'command': 'block-backup',
> > +  'data': { 'device': 'str', 'target': 'str', '*format': 'str',
> 
> Hmm - wondering if we should add an enum type for supported disk formats
> instead of using free-form strings.  The wire representation would be
> the same, and now's the time to do it before we add introspection (it's
> more than just this command impacted).

Interesting discussion about dynamic schema.  Since the wire format is
the same, I don't want to attempt solving the problem in the
block-backup series.