| Message ID | 20170214192525.18624-2-eblake@redhat.com |
|---|---|
| State | New |
| Headers | show |
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 <eblake@redhat.com> > Reviewed-by: Max Reitz <mreitz@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
On 02/15/2017 06:25 AM, Kevin Wolf wrote: > 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. Indeed; a slight tweak to qemu-iotests/097 exposes the problem. I'll include that in my next spin (although I note that Dan has patches on the list to split 097 into two tests, in order to give qcow coverage rather than just qcow2).
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)); + /* The zero flag is only supported by version 3 and newer */ if (s->qcow_version < 3) { return -ENOTSUP;