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block: drop unallocated_blocks_are_zero

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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>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200528094405.145708-10-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2020-05-28 12:44:04 +03:00 committed by Max Reitz
parent cdf9ebf18f
commit a2adbbf603
5 changed files with 13 additions and 15 deletions
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9
block/io.c
View File

@ -2406,7 +2406,7 @@ 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);
@ -2415,12 +2415,7 @@ 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;
}
}

1
block/qcow2.c
View File

@ -4987,7 +4987,6 @@ 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;

1
block/qed.c
View File

@ -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;
}

5
include/block/block.h
View File

@ -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
*/

12
include/block/block_int.h
View File

@ -123,7 +123,17 @@ 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 */