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block/io: Update BSC only if want_zero is true 

We update the block-status cache whenever we get new information from a
bdrv_co_block_status() call to the block driver.  However, if we have
passed want_zero=false to that call, it may flag areas containing zeroes
as data, and so we would update the block-status cache with wrong
information.

Therefore, we should not update the cache with want_zero=false.

Reported-by: Nir Soffer <nsoffer@redhat.com>
Fixes: 0bc329fbb0 ("block: block-status cache for data regions")
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220118170000.49423-2-hreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Hanna Reitz 2022-01-18 17:59:59 +01:00 committed by Eric Blake
parent 3a8fa0edd1
commit 113b727ce7
1 changed files with 5 additions and 1 deletions
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6
block/io.c
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@ -2497,8 +2497,12 @@ static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs,
* non-protocol nodes, and then it is never used. However, filling
* the cache requires an RCU update, so double check here to avoid
* such an update if possible.
*
* Check want_zero, because we only want to update the cache when we
* have accurate information about what is zero and what is data.
*/
if (ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
if (want_zero &&
ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
QLIST_EMPTY(&bs->children))
{
/*