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

[Kevin Wolf]

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 <address@hidden>
> Reviewed-by: Eric Blake <address@hidden>

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.

> +--- 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.

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.

Kevin