Re: [Qemu-devel] qemu-img: error while compressing, Input/output error

[Stefan Hajnoczi]

On Mon, Apr 15, 2013 at 1:00 PM, Ilkka Tengvall
<address@hidden> wrote:
> On 15.04.2013 09:52, Stefan Hajnoczi wrote:
>>
>> I discussed the bug with kwolf on Friday.  Although I sent a patch to
>> add an error message when the input image length is not a multiple of
>> cluster_size, Kevin pointed out that we can allow the final cluster to
>> be zero-padded beyond the end of the virtual disk.
>> Stefan
>
>
> I second that. As an end user it is just extra complication to do that
> manually. Especially if the device really ends at the non 64K boundary, it's
> extra trouble to extend the device first. Not to talk about complicating the
> auto build scripts by needing to add the size calculations before all
> compressions.
>
> In my case I don't mind if there is some extra bytes of zero at the end of a
> file size of hundreds of megs. I do understand the purity aspect though, not
> getting the exact same copy while doing the conversion back. Could there be
> a compatibility switch, that would handle the error automatically if one
> doesn't care about converting back to original image?

A compatibility option won't be necessary because the virtual disk
size will not be extended.  This means that the image can be converted
to raw without a change in disk size.

The trick is that although we will compress a padded cluster, the
virtual disk size will remain unchanged.  The zero bytes will not be
accessible, they will just automatically pad to the required
alignment.

Stefan