From 14a58a4e0c2e98a7d9232e1c229a531ca231133b Mon Sep 17 00:00:00 2001 From: Max Reitz Date: Tue, 10 Feb 2015 15:02:31 -0500 Subject: qcow2: Respect new_block in alloc_refcount_block() 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 Message-id: 1423598552-24301-2-git-send-email-mreitz@redhat.com Reviewed-by: Eric Blake Reviewed-by: Kevin Wolf Signed-off-by: Max Reitz --- block/qcow2-refcount.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'block') diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index dc8d186..6cbae1d 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -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; -- cgit v1.1