On 05/26/2016 06:48 AM, Eric Blake wrote:
is_zero_cluster() and is_zero_cluster_top_locked() are used only by qcow2_co_write_zeroes(). The former is too broad (we don't care if the sectors we are about to overwrite are non-zero, only that all other sectors in the cluster are zero), so it needs to be called up to twice but with smaller limits - rename it along with adding the neeeded parameter. The latter can be inlined for more compact code.The testsuite change shows that we now have a sparser top file when an unaligned write_zeroes overwrites the only portion of the backing file with data. Based on a patch proposal by Denis V. Lunev. CC: Denis V. Lunev <d...@openvz.org> Signed-off-by: Eric Blake <ebl...@redhat.com> --- block/qcow2.c | 47 +++++++++++++++++++++++----------------------- tests/qemu-iotests/154.out | 8 ++++---- 2 files changed, 27 insertions(+), 28 deletions(-) diff --git a/block/qcow2.c b/block/qcow2.c index 105fd5e..ecac399 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2406,26 +2406,19 @@ finish: } -static bool is_zero_cluster(BlockDriverState *bs, int64_t start) +static bool is_zero_sectors(BlockDriverState *bs, int64_t start, + uint32_t count) { - BDRVQcow2State *s = bs->opaque; int nr; BlockDriverState *file; - int64_t res = bdrv_get_block_status_above(bs, NULL, start, - s->cluster_sectors, &nr, &file); - return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == s->cluster_sectors; -} + int64_t res; -static bool is_zero_cluster_top_locked(BlockDriverState *bs, int64_t start) -{ - BDRVQcow2State *s = bs->opaque; - int nr = s->cluster_sectors; - uint64_t off; - int ret; - - ret = qcow2_get_cluster_offset(bs, start << BDRV_SECTOR_BITS, &nr, &off); - assert(nr == s->cluster_sectors); - return ret == QCOW2_CLUSTER_UNALLOCATED || ret == QCOW2_CLUSTER_ZERO; + if (!count) { + return true; + } + res = bdrv_get_block_status_above(bs, NULL, start, count, + &nr, &file); + return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == count; } static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs, @@ -2434,27 +2427,33 @@ static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs, int ret; BDRVQcow2State *s = bs->opaque; - int head = sector_num % s->cluster_sectors; - int tail = (sector_num + nb_sectors) % s->cluster_sectors; + uint32_t head = sector_num % s->cluster_sectors; + uint32_t tail = (sector_num + nb_sectors) % s->cluster_sectors; trace_qcow2_write_zeroes_start_req(qemu_coroutine_self(), sector_num, nb_sectors); - if (head != 0 || tail != 0) { + if (head || tail) { int64_t cl_start = sector_num - head; + uint64_t off; + int nr; assert(cl_start + s->cluster_sectors >= sector_num + nb_sectors); - sector_num = cl_start; - nb_sectors = s->cluster_sectors; - - if (!is_zero_cluster(bs, sector_num)) { + /* check whether remainder of cluster already reads as zero */ + if (!(is_zero_sectors(bs, cl_start, head) && + is_zero_sectors(bs, sector_num + nb_sectors, + -tail & (s->cluster_sectors - 1)))) {
can we have cluster_sectors != 2^n? In this case this bits logic will be broken.
