Re: [Qemu-devel] [PATCH v4 04/10] block: make 'top' argument to block-commit optional

[Eric Blake]

On 06/04/2014 07:51 AM, Jeff Cody wrote:
> Now that active layer block-commit is supported, the 'top' argument
> no longer needs to be mandatory.
> 
> Change it to optional, with the default being the active layer in the
> device chain.
> 
> Reviewed-by: Eric Blake <address@hidden>
> Reviewed-by: Benoit Canet <address@hidden>
> Signed-off-by: Jeff Cody <address@hidden>
> ---

Unrelated to my review, but I wish we had done a better job at making
the qemu 2.0 addition of active commit introspectible.  Had we made
_this_ patch at the same time, introspection would be possible by
creating a dummy blockdev, then attempting a block-commit that omits the
'top' argument (since the error message for a missing required argument
[old qemu] is different than the message for a blockdev that can't be
committed [new qemu]).  But since this change is in a different release
than where we supported active commit, I'm stuck coming up with some
reliable way to do a probe of whether active commit is supported so that
libvirt knows whether to expose active commit on to the end user.

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

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