Re: [Qemu-devel] QEMU online guest disk resize wrt host block devices

[Kevin Wolf]

Am 01.09.2011 17:56, schrieb Christoph Hellwig:
> On Thu, Sep 01, 2011 at 03:27:35PM +0100, Daniel P. Berrange wrote:
>> One other question too, when creating a qcow2 image via 'qemu-img create'
>> you can specify a 'prealloc' option to require metadata to be allocated
>> at time of creation.
>>
>> Should we have the same control at time of resize too. If the app had
>> originally created the qcow2 image with preallocated metadata, then
>> I'd expect they want to pre-allocate metadata when extending it too,
>> or is there no additional metadata allocation required when extending
>> an image ?
> 
> Sounds reasonable.  Keving, is there a sane way to implement this?

Implementing the functionality itself shouldn't be a big problem. The
big question is what the right interface would look like.

We have driver specific preallocation options, so we would end up with
something like this: bdrv_truncate(bs, int64_t size, char*
prealloc_mode). Not exactly nice. And is preallocation the only thing or
would we need to pass a whole option list like for image creation?

Of course, if this is a real requirement and not only a random thought,
we can always introduce a specific flag for the current use case and add
the generic thing only later when we have thought a bit more about it.

Kevin