qcow2: count_contiguous_clusters and compression

The function is not intended to be used on compressed clusters and will
not work correctly, if used anyway, since L2E_OFFSET_MASK is not the
right mask for determining the offset of compressed clusters. Therefore,
assert that the first cluster is not compressed and always include the
compression flag in the mask of significant flags, i.e., stop the search
as soon as a compressed cluster occurs.

Signed-off-by: Max Reitz <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 91d07f220331b4a9f1e1e6d32d27af94ca69dd13..8b2361a2ed67c79bc12e098385a56603ee2f6ac4 100644 (file)
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -284,12 +284,15 @@ static int count_contiguous_clusters(uint64_t nb_clusters, int cluster_size,
         uint64_t *l2_table, uint64_t start, uint64_t stop_flags)
 {
     int i;
-    uint64_t mask = stop_flags | L2E_OFFSET_MASK;
-    uint64_t offset = be64_to_cpu(l2_table[0]) & mask;
+    uint64_t mask = stop_flags | L2E_OFFSET_MASK | QCOW2_CLUSTER_COMPRESSED;
+    uint64_t first_entry = be64_to_cpu(l2_table[0]);
+    uint64_t offset = first_entry & mask;
 
     if (!offset)
         return 0;
 
+    assert(qcow2_get_cluster_type(first_entry) != QCOW2_CLUSTER_COMPRESSED);
+
     for (i = start; i < start + nb_clusters; i++) {
         uint64_t l2_entry = be64_to_cpu(l2_table[i]) & mask;
         if (offset + (uint64_t) i * cluster_size != l2_entry) {