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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;
}
}