From fc6b211f920a68f4c9c8db91ccc35ca95fe6683a Mon Sep 17 00:00:00 2001 From: Andrey Drobyshev Date: Tue, 11 Jul 2023 20:25:52 +0300 Subject: [PATCH] block/io: align requests to subcluster_size When target image is using subclusters, and we align the request during copy-on-read, it makes sense to align to subcluster_size rather than cluster_size. Otherwise we end up with unnecessary allocations. This commit renames bdrv_round_to_clusters() to bdrv_round_to_subclusters() and utilizes subcluster_size field of BlockDriverInfo to make necessary alignments. It affects copy-on-read as well as mirror job (which is using bdrv_round_to_clusters()). This change also fixes the following bug with failing assert (covered by the test in the subsequent commit): qemu-img create -f qcow2 base.qcow2 64K qemu-img create -f qcow2 -o extended_l2=on,backing_file=base.qcow2,backing_fmt=qcow2 img.qcow2 64K qemu-io -c "write -P 0xaa 0 2K" img.qcow2 qemu-io -C -c "read -P 0x00 2K 62K" img.qcow2 qemu-io: ../block/io.c:1236: bdrv_co_do_copy_on_readv: Assertion `skip_bytes < pnum' failed. Reviewed-by: Eric Blake Reviewed-by: Denis V. Lunev Signed-off-by: Andrey Drobyshev Reviewed-by: Vladimir Sementsov-Ogievskiy Signed-off-by: Stefan Hajnoczi Message-ID: <20230711172553.234055-3-andrey.drobyshev@virtuozzo.com> --- block/io.c | 50 ++++++++++++++++++++-------------------- block/mirror.c | 8 +++---- include/block/block-io.h | 8 +++---- 3 files changed, 33 insertions(+), 33 deletions(-) diff --git a/block/io.c b/block/io.c index 055fcf7438..76e7df18d8 100644 --- a/block/io.c +++ b/block/io.c @@ -728,21 +728,21 @@ BdrvTrackedRequest *coroutine_fn bdrv_co_get_self_request(BlockDriverState *bs) } /** - * Round a region to cluster boundaries + * Round a region to subcluster (if supported) or cluster boundaries */ void coroutine_fn GRAPH_RDLOCK -bdrv_round_to_clusters(BlockDriverState *bs, int64_t offset, int64_t bytes, - int64_t *cluster_offset, int64_t *cluster_bytes) +bdrv_round_to_subclusters(BlockDriverState *bs, int64_t offset, int64_t bytes, + int64_t *align_offset, int64_t *align_bytes) { BlockDriverInfo bdi; IO_CODE(); - if (bdrv_co_get_info(bs, &bdi) < 0 || bdi.cluster_size == 0) { - *cluster_offset = offset; - *cluster_bytes = bytes; + if (bdrv_co_get_info(bs, &bdi) < 0 || bdi.subcluster_size == 0) { + *align_offset = offset; + *align_bytes = bytes; } else { - int64_t c = bdi.cluster_size; - *cluster_offset = QEMU_ALIGN_DOWN(offset, c); - *cluster_bytes = QEMU_ALIGN_UP(offset - *cluster_offset + bytes, c); + int64_t c = bdi.subcluster_size; + *align_offset = QEMU_ALIGN_DOWN(offset, c); + *align_bytes = QEMU_ALIGN_UP(offset - *align_offset + bytes, c); } } @@ -1168,8 +1168,8 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t offset, int64_t bytes, void *bounce_buffer = NULL; BlockDriver *drv = bs->drv; - int64_t cluster_offset; - int64_t cluster_bytes; + int64_t align_offset; + int64_t align_bytes; int64_t skip_bytes; int ret; int max_transfer = MIN_NON_ZERO(bs->bl.max_transfer, @@ -1203,28 +1203,28 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t offset, int64_t bytes, * BDRV_REQUEST_MAX_BYTES (even when the original read did not), which * is one reason we loop rather than doing it all at once. */ - bdrv_round_to_clusters(bs, offset, bytes, &cluster_offset, &cluster_bytes); - skip_bytes = offset - cluster_offset; + bdrv_round_to_subclusters(bs, offset, bytes, &align_offset, &align_bytes); + skip_bytes = offset - align_offset; trace_bdrv_co_do_copy_on_readv(bs, offset, bytes, - cluster_offset, cluster_bytes); + align_offset, align_bytes); - while (cluster_bytes) { + while (align_bytes) { int64_t pnum; if (skip_write) { ret = 1; /* "already allocated", so nothing will be copied */ - pnum = MIN(cluster_bytes, max_transfer); + pnum = MIN(align_bytes, max_transfer); } else { - ret = bdrv_is_allocated(bs, cluster_offset, - MIN(cluster_bytes, max_transfer), &pnum); + ret = bdrv_is_allocated(bs, align_offset, + MIN(align_bytes, max_transfer), &pnum); if (ret < 0) { /* * Safe to treat errors in querying allocation as if * unallocated; we'll probably fail again soon on the * read, but at least that will set a decent errno. */ - pnum = MIN(cluster_bytes, max_transfer); + pnum = MIN(align_bytes, max_transfer); } /* Stop at EOF if the image ends in the middle of the cluster */ @@ -1242,7 +1242,7 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t offset, int64_t bytes, /* Must copy-on-read; use the bounce buffer */ pnum = MIN(pnum, MAX_BOUNCE_BUFFER); if (!bounce_buffer) { - int64_t max_we_need = MAX(pnum, cluster_bytes - pnum); + int64_t max_we_need = MAX(pnum, align_bytes - pnum); int64_t max_allowed = MIN(max_transfer, MAX_BOUNCE_BUFFER); int64_t bounce_buffer_len = MIN(max_we_need, max_allowed); @@ -1254,7 +1254,7 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t offset, int64_t bytes, } qemu_iovec_init_buf(&local_qiov, bounce_buffer, pnum); - ret = bdrv_driver_preadv(bs, cluster_offset, pnum, + ret = bdrv_driver_preadv(bs, align_offset, pnum, &local_qiov, 0, 0); if (ret < 0) { goto err; @@ -1266,13 +1266,13 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t offset, int64_t bytes, /* FIXME: Should we (perhaps conditionally) be setting * BDRV_REQ_MAY_UNMAP, if it will allow for a sparser copy * that still correctly reads as zero? */ - ret = bdrv_co_do_pwrite_zeroes(bs, cluster_offset, pnum, + ret = bdrv_co_do_pwrite_zeroes(bs, align_offset, pnum, BDRV_REQ_WRITE_UNCHANGED); } else { /* This does not change the data on the disk, it is not * necessary to flush even in cache=writethrough mode. */ - ret = bdrv_driver_pwritev(bs, cluster_offset, pnum, + ret = bdrv_driver_pwritev(bs, align_offset, pnum, &local_qiov, 0, BDRV_REQ_WRITE_UNCHANGED); } @@ -1301,8 +1301,8 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t offset, int64_t bytes, } } - cluster_offset += pnum; - cluster_bytes -= pnum; + align_offset += pnum; + align_bytes -= pnum; progress += pnum - skip_bytes; skip_bytes = 0; } diff --git a/block/mirror.c b/block/mirror.c index d3cacd1708..e213a892db 100644 --- a/block/mirror.c +++ b/block/mirror.c @@ -283,8 +283,8 @@ static int coroutine_fn mirror_cow_align(MirrorBlockJob *s, int64_t *offset, need_cow |= !test_bit((*offset + *bytes - 1) / s->granularity, s->cow_bitmap); if (need_cow) { - bdrv_round_to_clusters(blk_bs(s->target), *offset, *bytes, - &align_offset, &align_bytes); + bdrv_round_to_subclusters(blk_bs(s->target), *offset, *bytes, + &align_offset, &align_bytes); } if (align_bytes > max_bytes) { @@ -576,8 +576,8 @@ static void coroutine_fn mirror_iteration(MirrorBlockJob *s) int64_t target_offset; int64_t target_bytes; WITH_GRAPH_RDLOCK_GUARD() { - bdrv_round_to_clusters(blk_bs(s->target), offset, io_bytes, - &target_offset, &target_bytes); + bdrv_round_to_subclusters(blk_bs(s->target), offset, io_bytes, + &target_offset, &target_bytes); } if (target_offset == offset && target_bytes == io_bytes) { diff --git a/include/block/block-io.h b/include/block/block-io.h index 4415506e40..6db48f2d35 100644 --- a/include/block/block-io.h +++ b/include/block/block-io.h @@ -189,10 +189,10 @@ bdrv_get_info(BlockDriverState *bs, BlockDriverInfo *bdi); ImageInfoSpecific *bdrv_get_specific_info(BlockDriverState *bs, Error **errp); BlockStatsSpecific *bdrv_get_specific_stats(BlockDriverState *bs); -void bdrv_round_to_clusters(BlockDriverState *bs, - int64_t offset, int64_t bytes, - int64_t *cluster_offset, - int64_t *cluster_bytes); +void bdrv_round_to_subclusters(BlockDriverState *bs, + int64_t offset, int64_t bytes, + int64_t *cluster_offset, + int64_t *cluster_bytes); void bdrv_get_backing_filename(BlockDriverState *bs, char *filename, int filename_size);