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qcow2: Allow discard of final unaligned cluster

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As mentioned in commit 0c1bd46, we ignored requests to
discard the trailing cluster of an unaligned image.  While
discard is an advisory operation from the guest standpoint,
(and we are therefore free to ignore any request), our
qcow2 implementation exploits the fact that a discarded
cluster reads back as 0.  As long as we discard on cluster
boundaries, we are fine; but that means we could observe
non-zero data leaked at the tail of an unaligned image.

Enhance iotest 66 to cover this case, and fix the implementation
to honor a discard request on the final partial cluster.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-id: 20170407013709.18440-1-eblake@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Eric Blake 2017-04-06 20:37:09 -05:00 • committed by Max Reitz
parent f59adb3256
commit 048c5fd1bf
3 changed files with 21 additions and 10 deletions
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7
block/qcow2.c
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@ -2515,7 +2515,12 @@ static coroutine_fn int qcow2_co_pdiscard(BlockDriverState *bs,
if (!QEMU_IS_ALIGNED(offset | count, s->cluster_size)) {
assert(count < s->cluster_size);
return -ENOTSUP;
/* Ignore partial clusters, except for the special case of the
* complete partial cluster at the end of an unaligned file */
if (!QEMU_IS_ALIGNED(offset, s->cluster_size) ||
offset + count != bs->total_sectors * BDRV_SECTOR_SIZE) {
return -ENOTSUP;
}
}
qemu_co_mutex_lock(&s->lock);