Re: [Qemu-devel] [PATCH v6 11/11] iotests: Add test for potentially damaging repairs

[Max Reitz <mreitz@redhat.com>]

On 2014-10-21 at 16:12, Kevin Wolf wrote:
> Am 20.10.2014 um 16:35 hat Max Reitz geschrieben:
>> There are certain cases where repairing a qcow2 image might actually
>> damage it further (or rather, where repairing it has in fact damaged it
>> further with the old qcow2 check implementation). This should not
>> happen, so add a test for these cases.
>>
>> Furthermore, the repair function now repairs refblocks beyond the image
>> end by resizing the image accordingly. Add several tests for this as
>> well.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> Reviewed-by: Eric Blake <eblake@redhat.com>
> In case you didn't know: qemu-img handles hex offsets just fine, so
> there's no need to comment the hex value and then convert it to decimal
> for the real command.

Aha *g*

I did it that way in 060 and since then I just copied from there...

>> +--- Refblock is unallocated ---
>> +
>> +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
>> +Repairing refcount block 1 is outside image
>> +ERROR cluster 16 refcount=0 reference=1
>> +Rebuilding refcount structure
>> +Repairing cluster 1 refcount=1 reference=0
>> +Repairing cluster 2 refcount=1 reference=0
>> +Repairing cluster 16 refcount=1 reference=0
>> +The following inconsistencies were found and repaired:
>> +
>> +    0 leaked clusters
>> +    2 corruptions
>> +
>> +Double checking the fixed image now...
>> +No errors were found on the image.
>> +
>> +--- Signed overflow after the refblock ---
>> +
>> +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
>> +Repairing refcount block 1 is outside image
>> +ERROR could not resize image: Invalid argument
>> +Rebuilding refcount structure
>> +Repairing cluster 1 refcount=1 reference=0
>> +Repairing cluster 2 refcount=1 reference=0
>> +The following inconsistencies were found and repaired:
>> +
>> +    0 leaked clusters
>> +    1 corruptions
>> +
>> +Double checking the fixed image now...
>> +No errors were found on the image.
> This looks fishy. Compare this to the output of the previous case. We're
> now missing the corruption for the refblock because *nb_clusters wasn't
> increased.

I think we're rather missing the corruption for cluster 16 refcount=0. 
And I'd find that completely fine.

> Don't we actually run the risk of allocating a clusters during the
> refcount rebuild that was outside the image, but couldn't be repaired?
> Perhaps a resize failure needs to stop the repair.

The other way would be to unconditionally call inc_refcounts().

But I think it does not matter either way. If the refcount structure is 
rebuilt, all current refblocks are leaked anyway, so overwriting them is 
not an issue, I think.

Max