| Message ID | 20170308025428.1037-4-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 08.03.2017 03:54, Eric Blake wrote: > 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. 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 <eblake@redhat.com> > > --- > v6: avoid assertion on non-cluster-aligned image, use s->cluster_sectors > to avoid a shift, drop R-b > v5: no change > v4: new patch > --- > block/qcow2-cluster.c | 15 ++++++++------- > 1 file changed, 8 insertions(+), 7 deletions(-) Reviewed-by: Max Reitz <mreitz@redhat.com>
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 78c11d4..046fbd8 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1519,13 +1519,10 @@ 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, except at image end */ + assert(QEMU_IS_ALIGNED(offset, s->cluster_size)); + assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) || + end_offset == bs->total_sectors << BDRV_SECTOR_BITS); nb_clusters = size_to_clusters(s, end_offset - offset); @@ -1600,6 +1597,10 @@ 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_sectors)); + /* The zero flag is only supported by version 3 and newer */ if (s->qcow_version < 3) { return -ENOTSUP;
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. 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 <eblake@redhat.com> --- v6: avoid assertion on non-cluster-aligned image, use s->cluster_sectors to avoid a shift, drop R-b v5: no change v4: new patch --- block/qcow2-cluster.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-)