Re: [Qemu-devel] [PATCH v7 for 2.1 4/4] block: add QAPI command to allow live backing file change

[Eric Blake <eblake@redhat.com>]

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On 06/25/2014 01:40 PM, Jeff Cody wrote:
> This allows a user to make a live change to the backing file recorded in
> an open image.
> 
> The image file to modify can be specified 2 ways:
> 
> 1) image filename
> 2) image node-name
> 
> Note: this does not cause the backing file itself to be reopened; it
> merely changes the backing filename in the image file structure, and
> in internal BDS structures.
> 
> It is the responsibility of the user to pass a filename string that
> can be resolved when the image chain is reopened, and the filename
> string is not validated.
> 
> A good analogy for this command is that it is a live version of
> 'qemu-img rebase -u', with respect to changing the backing file string.

For 2.1, did we want to limit this command to only affecting the active
layer (and failing if it was attempted on a backing file), in order to
simplify dealing with op-blocker work?  Having the command exist, even
if it is limited in nature, is all the more libvirt wants right now; and
it's easier to relax a constraint in a future release than it is to
release something now and have to keep it working even after we rework
op-blockers in the future.

> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Jeff Cody <jcody@redhat.com>

I'm still okay with this patch as-is, if we are okay with the ability to
rename the backing file of a non-active node.

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


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