qcow2: Add offset_to_sc_index()

For a given offset, return the subcluster number within its cluster
(i.e. with 32 subclusters per cluster it returns a number between 0
and 31).

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <56e3e4ac0d827c6a2f5f259106c5ddb7c4ca2653.1594396418.git.berto@igalia.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

diff --git a/block/qcow2.h b/block/qcow2.h
index eee4c8de9ca4d4945be6aeea3792a1c1643b8dc8..2503374677e8f5a982b23816603b9a4b1969cb7f 100644 (file)
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -581,6 +581,11 @@ static inline int offset_to_l2_slice_index(BDRVQcow2State *s, int64_t offset)
     return (offset >> s->cluster_bits) & (s->l2_slice_size - 1);
 }
 
+static inline int offset_to_sc_index(BDRVQcow2State *s, int64_t offset)
+{
+    return (offset >> s->subcluster_bits) & (s->subclusters_per_cluster - 1);
+}
+
 static inline int64_t qcow2_vm_state_offset(BDRVQcow2State *s)
 {
     return (int64_t)s->l1_vm_state_index << (s->cluster_bits + s->l2_bits);