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qcow2: Respect new_block in alloc_refcount_block()

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When choosing a new place for the refcount table, alloc_refcount_block()
tries to infer the number of clusters used so far from its argument
cluster_index (which comes from the idea that if any cluster with an
index greater than cluster_index was in use, the refcount table would
have to be big enough already to describe cluster_index).

However, there is a cluster that may be at or after cluster_index, and
which is not covered by the refcount structures, and that is the new
refcount block new_block. Therefore, it should be taken into account for
the blocks_used calculation.

Also, because new_block already describes (or is intended to describe)
cluster_index, we may not put the new refcount structures there.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 1423598552-24301-2-git-send-email-mreitz@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Max Reitz 2015-02-10 15:02:31 -05:00
parent 2867ce4ab8
commit 14a58a4e0c
1 changed files with 14 additions and 2 deletions
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16
block/qcow2-refcount.c
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@ -466,8 +466,20 @@ static int alloc_refcount_block(BlockDriverState *bs,
*/
BLKDBG_EVENT(bs->file, BLKDBG_REFTABLE_GROW);
/* Calculate the number of refcount blocks needed so far */
uint64_t blocks_used = DIV_ROUND_UP(cluster_index, s->refcount_block_size);
/* Calculate the number of refcount blocks needed so far; this will be the
* basis for calculating the index of the first cluster used for the
* self-describing refcount structures which we are about to create.
*
* Because we reached this point, there cannot be any refcount entries for
* cluster_index or higher indices yet. However, because new_block has been
* allocated to describe that cluster (and it will assume this role later
* on), we cannot use that index; also, new_block may actually have a higher
* cluster index than cluster_index, so it needs to be taken into account
* here (and 1 needs to be added to its value because that cluster is used).
*/
uint64_t blocks_used = DIV_ROUND_UP(MAX(cluster_index + 1,
(new_block >> s->cluster_bits) + 1),
s->refcount_block_size);
if (blocks_used > QCOW_MAX_REFTABLE_SIZE / sizeof(uint64_t)) {
return -EFBIG;