[Qemu-devel] [RFC PATCH 03/16] qcow2: Ignore reserved bits in count_contiguous_clusters()

[Kevin Wolf <kwolf@redhat.com>]

Until now, count_contiguous_clusters() has an argument that allowed to
specify flags that should be ignored in the comparison, i.e. that are
allowed to change between contiguous clusters.

This patch changes the function so that it ignores all flags by default
now and you need to pass the flags on which it should stop.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2-cluster.c |   38 ++++++++++++++++++++++++++++----------
 1 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 44d13de..9547fa9 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -246,28 +246,44 @@ fail:
     return ret;
 }
 
+/*
+ * Checks how many clusters in a given L2 table are contiguous in the image
+ * file. As soon as one of the flags in the bitmask stop_flags changes compared
+ * to the first cluster, the search is stopped and the cluster is not counted
+ * as contiguous. (This allows it, for example, to stop at the first compressed
+ * cluster which may require a different handling)
+ */
 static int count_contiguous_clusters(uint64_t nb_clusters, int cluster_size,
-        uint64_t *l2_table, uint64_t start, uint64_t mask)
+        uint64_t *l2_table, uint64_t start, uint64_t stop_flags)
 {
     int i;
-    uint64_t offset = be64_to_cpu(l2_table[0]) & ~mask;
+    uint64_t mask = stop_flags | L2E_OFFSET_MASK;
+    uint64_t offset = be64_to_cpu(l2_table[0]) & mask;
 
     if (!offset)
         return 0;
 
-    for (i = start; i < start + nb_clusters; i++)
-        if (offset + (uint64_t) i * cluster_size != (be64_to_cpu(l2_table[i]) & ~mask))
+    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) {
             break;
+        }
+    }
 
 	return (i - start);
 }
 
 static int count_contiguous_free_clusters(uint64_t nb_clusters, uint64_t *l2_table)
 {
-    int i = 0;
+    int i;
 
-    while(nb_clusters-- && l2_table[i] == 0)
-        i++;
+    for (i = 0; i < nb_clusters; i++) {
+        int type = qcow2_get_cluster_type(be64_to_cpu(l2_table[i]));
+
+        if (type != QCOW2_CLUSTER_UNALLOCATED) {
+            break;
+        }
+    }
 
     return i;
 }
@@ -444,7 +460,7 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
     case QCOW2_CLUSTER_NORMAL:
         /* how many allocated clusters ? */
         c = count_contiguous_clusters(nb_clusters, s->cluster_size,
-                &l2_table[l2_index], 0, QCOW_OFLAG_COPIED);
+                &l2_table[l2_index], 0, QCOW_OFLAG_COMPRESSED);
         *cluster_offset &= L2E_OFFSET_MASK;
         break;
     }
@@ -696,7 +712,8 @@ static int count_cow_clusters(BDRVQcowState *s, int nb_clusters,
 
     while (i < nb_clusters) {
         i += count_contiguous_clusters(nb_clusters - i, s->cluster_size,
-                &l2_table[l2_index], i, 0);
+                &l2_table[l2_index], i,
+                QCOW_OFLAG_COPIED | QCOW_OFLAG_COMPRESSED);
         if ((i >= nb_clusters) || be64_to_cpu(l2_table[l2_index + i])) {
             break;
         }
@@ -854,7 +871,8 @@ again:
     if (cluster_offset & QCOW_OFLAG_COPIED) {
         /* We keep all QCOW_OFLAG_COPIED clusters */
         keep_clusters = count_contiguous_clusters(nb_clusters, s->cluster_size,
-                                                  &l2_table[l2_index], 0, 0);
+                                                  &l2_table[l2_index], 0,
+                                                  QCOW_OFLAG_COPIED);
         assert(keep_clusters <= nb_clusters);
         nb_clusters -= keep_clusters;
     } else {
-- 
1.7.6.5