Currently this field only set by qed and qcow2. But in fact, all
backing-supporting formats (parallels, qcow, qcow2, qed, vmdk) share
these 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 <vsementsov@virtuozzo.com>
---
include/block/block.h | 5 -----
include/block/block_int.h | 12 +++++++++++-
block/io.c | 9 ++-------
block/qcow2.c | 1 -
block/qed.c | 1 -
5 files changed, 13 insertions(+), 15 deletions(-)
diff --git a/include/block/block.h b/include/block/block.h
index 931003a476..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
*/
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 92335f33c7..8fac6c3ce2 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -115,7 +115,17 @@ 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:
+ * - fill buffer with zeros if there is no backing file
+ * - read from the backing file otherwise, where the block layer
+ * takes care of reading zeros beyond EOF if backing file is short
+ */
bool supports_backing;
/* For handling image reopen for split or non-split files */
diff --git a/block/io.c b/block/io.c
index 00e7371d50..484adec5a1 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2385,7 +2385,7 @@ 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) {
+ } else if (want_zero && bs->drv->supports_backing) {
if (bs->backing) {
BlockDriverState *bs2 = bs->backing->bs;
int64_t size2 = bdrv_getlength(bs2);
@@ -2394,12 +2394,7 @@ static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs,
ret |= BDRV_BLOCK_ZERO;
}
} else {
- BlockDriverInfo bdi;
- int ret2 = bdrv_get_info(bs, &bdi);
-
- if (ret2 == 0 && bdi.unallocated_blocks_are_zero) {
- ret |= BDRV_BLOCK_ZERO;
- }
+ 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