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[Qemu-devel] [PATCH 1/2] qcow2: Respect new_block in alloc_refcount_bloc
From: |
Max Reitz |
Subject: |
[Qemu-devel] [PATCH 1/2] qcow2: Respect new_block in alloc_refcount_block() |
Date: |
Tue, 10 Feb 2015 15:02:31 -0500 |
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 <address@hidden>
---
block/qcow2-refcount.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 9b80ca7..b956365 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -326,8 +326,20 @@ 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;
--
2.1.0