Re: [Qemu-devel] [PATCH 2/2] block: in commit, determine base image from the top image

[Eric Blake <eblake@redhat.com>]

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On 10/09/2012 11:56 PM, Jeff Cody wrote:
> This simplifies some code and error checking, and also fixes a bug.
> 
> bdrv_find_backing_image() should only be passed absolute filenames,
> or filenames relative to the chain.  In the QMP message handler for
> block commit, when looking up the base do so from the determined top
> image, so we know it is reachable from top.
> 
> Signed-off-by: Jeff Cody <jcody@redhat.com>
> ---
>  block/commit.c |  9 ---------
>  blockdev.c     | 21 +++++++++++----------
>  2 files changed, 11 insertions(+), 19 deletions(-)
> 

> @@ -1182,6 +1172,17 @@ void qmp_block_commit(const char *device,
>          return;
>      }
>  
> +    if (base && has_base) {
> +        base_bs = bdrv_find_backing_image(top_bs, base);

In particular, if I have the chain:

/dir1/base <- /dir1/snap1(base) <- /dir2/base(/dir1/snap1) <-
/dir2/snap2(base)

and request a commit of "top":"/dir1/snap1", "base":"base", then this
new code will now look up base relative to /dir1/snap1 and find
/dir1/base and proceed with the commit; whereas the old code would look
up base relative to /dir2/snap2 and find /dir2/base and complain that
the arguments were swapped.

I can live with those semantics.

Reviewed-by: Eric Blake <eblake@redhat.com>

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


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