Currently this field only set by qed and qcow2. But in fact, all backing-supporting formats (parallels, qcow, qcow2, qed, vmdk) share this semantics: on unallocated blocks, if there is no backing file they just memset the buffer with zeroes.
So, document this behavior for .supports_backing and drop .unallocated_blocks_are_zero Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> --- include/block/block.h | 6 ------ include/block/block_int.h | 13 ++++++++++++- block.c | 15 --------------- block/io.c | 8 ++++---- block/qcow2.c | 1 - block/qed.c | 1 - 6 files changed, 16 insertions(+), 28 deletions(-) diff --git a/include/block/block.h b/include/block/block.h index 8b62429aa4..db1cb503ec 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -21,11 +21,6 @@ typedef struct BlockDriverInfo { /* offset at which the VM state can be saved (0 if not possible) */ int64_t vm_state_offset; bool is_dirty; - /* - * True if unallocated blocks read back as zeroes. This is equivalent - * to the LBPRZ flag in the SCSI logical block provisioning page. - */ - bool unallocated_blocks_are_zero; /* * True if this block driver only supports compressed writes */ @@ -431,7 +426,6 @@ int bdrv_co_pdiscard(BdrvChild *child, int64_t offset, int64_t bytes); int bdrv_has_zero_init_1(BlockDriverState *bs); int bdrv_has_zero_init(BlockDriverState *bs); int bdrv_has_zero_init_truncate(BlockDriverState *bs); -bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs); bool bdrv_can_write_zeroes_with_unmap(BlockDriverState *bs); int bdrv_block_status(BlockDriverState *bs, int64_t offset, int64_t bytes, int64_t *pnum, int64_t *map, diff --git a/include/block/block_int.h b/include/block/block_int.h index 92335f33c7..c156b22c6b 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -115,7 +115,18 @@ struct BlockDriver { */ bool bdrv_needs_filename; - /* Set if a driver can support backing files */ + /* + * Set if a driver can support backing files. This also implies the + * following semantics: + * + * - Return status 0 of .bdrv_co_block_status means that corresponding + * blocks are not allocated in this layer of backing-chain + * - For such (unallocated) blocks, read will: + * - read from backing file if there is one and big enough + * - fill buffer with zeroes if there is no backing file + * - space after EOF of the backing file considered as zero + * (corresponding part of read-buffer must be zeroed by driver) + */ bool supports_backing; /* For handling image reopen for split or non-split files */ diff --git a/block.c b/block.c index cf5c19b1db..0283fdecbc 100644 --- a/block.c +++ b/block.c @@ -5305,21 +5305,6 @@ int bdrv_has_zero_init_truncate(BlockDriverState *bs) return 0; } -bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs) -{ - BlockDriverInfo bdi; - - if (bs->backing) { - return false; - } - - if (bdrv_get_info(bs, &bdi) == 0) { - return bdi.unallocated_blocks_are_zero; - } - - return false; -} - bool bdrv_can_write_zeroes_with_unmap(BlockDriverState *bs) { if (!(bs->open_flags & BDRV_O_UNMAP)) { diff --git a/block/io.c b/block/io.c index a4f9714230..484adec5a1 100644 --- a/block/io.c +++ b/block/io.c @@ -2385,16 +2385,16 @@ static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs, if (ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) { ret |= BDRV_BLOCK_ALLOCATED; - } else if (want_zero) { - if (bdrv_unallocated_blocks_are_zero(bs)) { - ret |= BDRV_BLOCK_ZERO; - } else if (bs->backing) { + } else if (want_zero && bs->drv->supports_backing) { + if (bs->backing) { BlockDriverState *bs2 = bs->backing->bs; int64_t size2 = bdrv_getlength(bs2); if (size2 >= 0 && offset >= size2) { ret |= BDRV_BLOCK_ZERO; } + } else { + ret |= BDRV_BLOCK_ZERO; } } diff --git a/block/qcow2.c b/block/qcow2.c index 2ba0b17c39..dc3c0aac2b 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -4858,7 +4858,6 @@ err: static int qcow2_get_info(BlockDriverState *bs, BlockDriverInfo *bdi) { BDRVQcow2State *s = bs->opaque; - bdi->unallocated_blocks_are_zero = true; bdi->cluster_size = s->cluster_size; bdi->vm_state_offset = qcow2_vm_state_offset(s); return 0; diff --git a/block/qed.c b/block/qed.c index b0fdb8f565..fb7833dc8b 100644 --- a/block/qed.c +++ b/block/qed.c @@ -1514,7 +1514,6 @@ static int bdrv_qed_get_info(BlockDriverState *bs, BlockDriverInfo *bdi) memset(bdi, 0, sizeof(*bdi)); bdi->cluster_size = s->header.cluster_size; bdi->is_dirty = s->header.features & QED_F_NEED_CHECK; - bdi->unallocated_blocks_are_zero = true; return 0; } -- 2.21.0