Am 14.02.2017 um 20:25 hat Eric Blake geschrieben:
> qcow2_discard_clusters() is set up to silently ignore sub-cluster
> head or tail on unaligned requests. However, it is easy to audit
> the various callers: qcow2_snapshot_create() has always passed
> aligned data since the call was introduced in 1ebf561;
> qcow2_co_pdiscard() has passed aligned clusters since commit
> ecdbead taught the block layer the preferred discard alignment (the
> block layer can still pass sub-cluster values, but those are
> handled directly in qcow2_co_pdiscard()); and qcow2_make_empty()
> was fixed to pass aligned clusters in commit a3e1505.
I don't think this is true for the very part in the image if the image
size isn't cluster aligned:
ret = qcow2_discard_clusters(bs, start_sector * BDRV_SECTOR_SIZE,
MIN(sector_step,
bs->total_sectors - start_sector),
QCOW2_DISCARD_SNAPSHOT, true);
sector_step is alright after commit a3e1505, but bs->total_sectors can
be unaligned.
The other callers look okay.
> Replace
> rounding with assertions to hold us to the tighter contract,
> eliminating the now-impossible case of an early exit for a
> sub-cluster request.
>
> qcow2_zero_clusters() has always been called with cluster-aligned
> arguments from its lone caller qcow2_co_pwrite_zeroes() (like
> qcow2_co_pdiscard(), the caller takes care of sub-cluster requests
> from the block layer; and qcow2_zero_clusters() would have
> misbehaved on unaligned requests), but it deserves the same
> assertion for symmetry.
>
> Signed-off-by: Eric Blake <ebl...@redhat.com>
> Reviewed-by: Max Reitz <mre...@redhat.com>
>
> ---
> v5: no change
> v4: new patch
> ---
> block/qcow2-cluster.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 928c1e2..3304a15 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1521,13 +1521,9 @@ int qcow2_discard_clusters(BlockDriverState *bs,
> uint64_t offset,
>
> end_offset = offset + (nb_sectors << BDRV_SECTOR_BITS);
>
> - /* Round start up and end down */
> - offset = align_offset(offset, s->cluster_size);
> - end_offset = start_of_cluster(s, end_offset);
> -
> - if (offset > end_offset) {
> - return 0;
> - }
> + /* Caller must pass aligned values */
> + assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
> + assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size));
>
> nb_clusters = size_to_clusters(s, end_offset - offset);
>
> @@ -1602,6 +1598,10 @@ int qcow2_zero_clusters(BlockDriverState *bs, uint64_t
> offset, int nb_sectors,
> uint64_t nb_clusters;
> int ret;
>
> + /* Caller must pass aligned values */
> + assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
> + assert(QEMU_IS_ALIGNED(nb_sectors, s->cluster_size >> BDRV_SECTOR_BITS));
Maybe using s->cluster_sectors is nicer than doing the shift here. Not
too important, the code is replaced in the next patch anyway.
> /* The zero flag is only supported by version 3 and newer */
> if (s->qcow_version < 3) {
> return -ENOTSUP;
Kevin
