From: Vincent Vanlaer <[email protected]> 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 <[email protected]> Reviewed-by: Vladimir Sementsov-Ogievskiy <[email protected]> Message-Id: <[email protected]> Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]> (cherry picked from commit 6f3199f99600fe75f32f78574e507f347de80854) Signed-off-by: Michael Tokarev <[email protected]> diff --git a/block/commit.c b/block/commit.c index 5c6596a52e..7cc8c0f0df 100644 --- a/block/commit.c +++ b/block/commit.c @@ -150,19 +150,39 @@ 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); } -- 2.47.3
