diff options
| -rw-r--r-- | block/io.c | 27 | ||||
| -rw-r--r-- | block/qcow2.c | 35 | ||||
| -rw-r--r-- | include/block/block.h | 2 |
3 files changed, 48 insertions, 16 deletions
@@ -2447,6 +2447,33 @@ int bdrv_block_status(BlockDriverState *bs, int64_t offset, int64_t bytes, offset, bytes, pnum, map, file); } +/* + * Check @bs (and its backing chain) to see if the range defined + * by @offset and @bytes is known to read as zeroes. + * Return 1 if that is the case, 0 otherwise and -errno on error. + * This test is meant to be fast rather than accurate so returning 0 + * does not guarantee non-zero data. + */ +int coroutine_fn bdrv_co_is_zero_fast(BlockDriverState *bs, int64_t offset, + int64_t bytes) +{ + int ret; + int64_t pnum = bytes; + + if (!bytes) { + return 1; + } + + ret = bdrv_common_block_status_above(bs, NULL, false, false, offset, + bytes, &pnum, NULL, NULL); + + if (ret < 0) { + return ret; + } + + return (pnum == bytes) && (ret & BDRV_BLOCK_ZERO); +} + int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset, int64_t bytes, int64_t *pnum) { diff --git a/block/qcow2.c b/block/qcow2.c index b6cb4db..4274806 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2387,26 +2387,26 @@ static bool merge_cow(uint64_t offset, unsigned bytes, return false; } -static bool is_unallocated(BlockDriverState *bs, int64_t offset, int64_t bytes) -{ - int64_t nr; - return !bytes || - (!bdrv_is_allocated_above(bs, NULL, false, offset, bytes, &nr) && - nr == bytes); -} - -static bool is_zero_cow(BlockDriverState *bs, QCowL2Meta *m) +/* + * Return 1 if the COW regions read as zeroes, 0 if not, < 0 on error. + * Note that returning 0 does not guarantee non-zero data. + */ +static int is_zero_cow(BlockDriverState *bs, QCowL2Meta *m) { /* * This check is designed for optimization shortcut so it must be * efficient. - * Instead of is_zero(), use is_unallocated() as it is faster (but not - * as accurate and can result in false negatives). + * Instead of is_zero(), use bdrv_co_is_zero_fast() as it is + * faster (but not as accurate and can result in false negatives). */ - return is_unallocated(bs, m->offset + m->cow_start.offset, - m->cow_start.nb_bytes) && - is_unallocated(bs, m->offset + m->cow_end.offset, - m->cow_end.nb_bytes); + int ret = bdrv_co_is_zero_fast(bs, m->offset + m->cow_start.offset, + m->cow_start.nb_bytes); + if (ret <= 0) { + return ret; + } + + return bdrv_co_is_zero_fast(bs, m->offset + m->cow_end.offset, + m->cow_end.nb_bytes); } static int handle_alloc_space(BlockDriverState *bs, QCowL2Meta *l2meta) @@ -2432,7 +2432,10 @@ static int handle_alloc_space(BlockDriverState *bs, QCowL2Meta *l2meta) continue; } - if (!is_zero_cow(bs, m)) { + ret = is_zero_cow(bs, m); + if (ret < 0) { + return ret; + } else if (ret == 0) { continue; } diff --git a/include/block/block.h b/include/block/block.h index d16c401..c9d7c58 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -508,6 +508,8 @@ int bdrv_is_allocated(BlockDriverState *bs, int64_t offset, int64_t bytes, int bdrv_is_allocated_above(BlockDriverState *top, BlockDriverState *base, bool include_base, int64_t offset, int64_t bytes, int64_t *pnum); +int coroutine_fn bdrv_co_is_zero_fast(BlockDriverState *bs, int64_t offset, + int64_t bytes); bool bdrv_is_read_only(BlockDriverState *bs); int bdrv_can_set_read_only(BlockDriverState *bs, bool read_only, |