On 10/03/2017 09:00 PM, Eric Blake wrote: > Compare the following images with all-zero contents: > $ truncate --size 1M A > $ qemu-img create -f qcow2 -o preallocation=off B 1G > $ qemu-img create -f qcow2 -o preallocation=metadata C 1G >
> Signed-off-by: Eric Blake <ebl...@redhat.com>
> Reviewed-by: John Snow <js...@redhat.com>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
>
> +++ b/qemu-img.c
> @@ -1481,11 +1481,11 @@ static int img_compare(int argc, char **argv)
> while (sector_num < progress_base) {
> int64_t count;
>
> - ret = bdrv_is_allocated_above(blk_bs(blk_over), NULL,
> + ret = bdrv_block_status_above(blk_bs(blk_over), NULL,
Just now noticing: in this function, ret is 32-bit, but
bdrv_block_status_above() returns 64-bit values...
> sector_num * BDRV_SECTOR_SIZE,
> (progress_base - sector_num) *
> BDRV_SECTOR_SIZE,
> - &count);
> + &count, NULL);
> if (ret < 0) {
...which could make for a false positive in a static checker (none of
our implementations return a negative value beyond INT_MIN for wrapping
to be a serious concern). So that's yet another reason why I am liking
Kevin's proposal to split the returned offset to be a by-reference
parameter rather than squashed into the return type, as it will let me
use a 32-bit return type and avoid worrying about this corner case.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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