Re: [Qemu-devel] [PATCHv4] qemu-img rebase: use empty string to rebase without backing file

[Eric Blake]

On 10/19/2012 10:46 AM, Kevin Wolf wrote:
>> As it happens, we despite what Eric Blake said, we couldn't get an unsafe
>> rebase to no backing file to work with the existing code (with our without
>> our patch). The second option may fix this bug. Reading line 1497, is this
>> because the semantic is not 'an empty string', but 'omit -b entirely'?
>> This behaviour is undocumented in the manpage which specifies -b as a
>> compulsory option. If so, that's a bit unfortunate as we now have different
>> semantics with and without -u. Note if no -b parameter is supplied, there
>> is also a possible null pointer exception at line 1693 (null passed to
>> error_report).
> 
> Right. I think not passing -b at all or passing an empty string should
> have the same meaning, namely removing the backing file reference. I
> won't try to modify this patch to do this, though, we can do it on top.

Agreed - a future patch that makes -b optional rather than mandatory,
where '-b ""' and omitting the argument have the same semantics whether
or not -u is present, would be nice.

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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