Re: [Qemu-devel] [PATCH] qemu-img rebase: allow backing file to be specified as '-'

[Eric Blake <eblake@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 1294 bytes --]

On 10/15/2012 12:07 PM, Eric Blake wrote:
> On 10/15/2012 11:29 AM, Alex Bligh wrote:
>> This patch allows qemu-img rebase to rebase an image to
>> have no backing file, as opposed to merely allowing it to
>> rebase to an existing backing file.
> 
> You can already do that by rebasing to the empty string.  And it is
> feasible (although unlikely) to have a file named '-', where your patch
> would make it impossible to use that file directly (although you could
> still use './-').  NACK.
> 
> $ qemu-img info bar
> image: bar
> file format: qcow2
> virtual size: 0 (0 bytes)
> disk size: 192K
> cluster_size: 65536
> backing file: foo
> $ qemu-img rebase -u -b ''  bar
> $ qemu-img info bar
> image: bar
> file format: qcow2
> virtual size: 0 (0 bytes)
> disk size: 192K
> cluster_size: 65536

On the other hand, if you don't use -u, then qemu-img complains:

$ qemu-img rebase  -b ''  bar
qemu-img: Could not open new backing file ''

So I think a better patch would be to allow rebase-by-pull to work the
same as unsafe rebase, by honoring the empty string as a request to pull
the entire chain into the destination and leave no backing file.

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


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 617 bytes --]