[RFC PATCH v2 07/26] qcow2: Add subcluster-related fields to BDRVQcow2State

[Alberto Garcia <berto@igalia.com>]

This patch adds the following new fields to BDRVQcow2State:

- subclusters_per_cluster: Number of subclusters in a cluster
- subcluster_size: The size of each subcluster, in bytes
- subcluster_bits: No. of bits so 1 << subcluster_bits = subcluster_size

Images without subclusters are treated as if they had exactly one,
with subcluster_size = cluster_size.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2.c | 5 +++++
 block/qcow2.h | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/block/qcow2.c b/block/qcow2.c
index 0bc69e6996..ed8b81c7b7 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1342,6 +1342,11 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
         }
     }
 
+    s->subclusters_per_cluster =
+        has_subclusters(s) ? QCOW_MAX_SUBCLUSTERS_PER_CLUSTER : 1;
+    s->subcluster_size = s->cluster_size / s->subclusters_per_cluster;
+    s->subcluster_bits = ctz32(s->subcluster_size);
+
     /* Check support for various header values */
     if (header.refcount_order > 6) {
         error_setg(errp, "Reference count entry width too large; may not "
diff --git a/block/qcow2.h b/block/qcow2.h
index b3826b37c1..278ca41314 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -75,6 +75,8 @@
 /* The cluster reads as all zeros */
 #define QCOW_OFLAG_ZERO (1ULL << 0)
 
+#define QCOW_MAX_SUBCLUSTERS_PER_CLUSTER 32
+
 #define MIN_CLUSTER_BITS 9
 #define MAX_CLUSTER_BITS 21
 
@@ -277,6 +279,9 @@ typedef struct BDRVQcow2State {
     int cluster_bits;
     int cluster_size;
     int l2_slice_size;
+    int subcluster_bits;
+    int subcluster_size;
+    int subclusters_per_cluster;
     int l2_bits;
     int l2_size;
     int l1_size;
-- 
2.20.1