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 <address@hidden>
Signed-off-by: Eric Blake <address@hidden>
---
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)))) {