Non-active block commits do not discard blocks only containing zeros,
causing images to lose sparseness after the commit. This commit fixes
that by writing zero blocks using blk_co_pwrite_zeroes rather than
writing them out as any other arbitrary data.
Signed-off-by: Vincent Vanlaer <libvirt-e6954...@volkihar.be>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
---
block/commit.c | 38 +++++++++++++++++++++++++++++---------
1 file changed, 29 insertions(+), 9 deletions(-)
diff --git a/block/commit.c b/block/commit.c
index 5c24c8b80a..ca1a367b41 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -149,19 +149,39 @@ static int commit_iteration(CommitBlockJob *s, int64_t
offset,
}
if (ret & BDRV_BLOCK_ALLOCATED) {
- assert(bytes < SIZE_MAX);
+ if (ret & BDRV_BLOCK_ZERO) {
+ /*
+ * If the top (sub)clusters are smaller than the base
+ * (sub)clusters, this will not unmap unless the underlying device
+ * does some tracking of these requests. Ideally, we would find
+ * the maximal extent of the zero clusters.
+ */
+ ret = blk_co_pwrite_zeroes(s->base, offset, bytes,
+ BDRV_REQ_MAY_UNMAP);
+ if (ret < 0) {
+ error_in_source = false;
+ goto fail;
+ }
+ } else {
+ assert(bytes < SIZE_MAX);
- ret = blk_co_pread(s->top, offset, bytes, buf, 0);
- if (ret < 0) {
- goto fail;
- }
+ ret = blk_co_pread(s->top, offset, bytes, buf, 0);
+ if (ret < 0) {
+ goto fail;
+ }
- ret = blk_co_pwrite(s->base, offset, bytes, buf, 0);
- if (ret < 0) {
- error_in_source = false;
- goto fail;
+ ret = blk_co_pwrite(s->base, offset, bytes, buf, 0);
+ if (ret < 0) {
+ error_in_source = false;
+ goto fail;
+ }
}
+ /*
+ * Whether zeroes actually end up on disk depends on the details of
+ * the underlying driver. Therefore, this might rate limit more than
+ * is necessary.
+ */
block_job_ratelimit_processed_bytes(&s->common, bytes);
}
--
2.44.1
