qcow2: Decouple cluster allocation from cluster reuse code

This moves some code that prepares the allocation of new clusters to
where the actual allocation happens. This is the minimum required to be
able to move it to a separate function in the next patch.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/qcow2-cluster.c

@@ -946,10 +946,7 @@ again:
 
     cluster_offset = be64_to_cpu(l2_table[l2_index]);
 
-    /*
-     * Check how many clusters are already allocated and don't need COW, and how
-     * many need a new allocation.
-     */
+    /* Check how many clusters are already allocated and don't need COW */
     if (qcow2_get_cluster_type(cluster_offset) == QCOW2_CLUSTER_NORMAL
         && (cluster_offset & QCOW_OFLAG_COPIED))
     {
@@ -965,17 +962,6 @@ again:
         cluster_offset = 0;
     }
 
-    if (nb_clusters > 0) {
-        /* For the moment, overwrite compressed clusters one by one */
-        uint64_t entry = be64_to_cpu(l2_table[l2_index + keep_clusters]);
-        if (entry & QCOW_OFLAG_COMPRESSED) {
-            nb_clusters = 1;
-        } else {
-            nb_clusters = count_cow_clusters(s, nb_clusters, l2_table,
-                                             l2_index + keep_clusters);
-        }
-    }
-
     cluster_offset &= L2E_OFFSET_MASK;
 
     /*
@@ -996,6 +982,25 @@ again:
         uint64_t alloc_cluster_offset;
         uint64_t keep_bytes = keep_clusters * s->cluster_size;
 
+        ret = get_cluster_table(bs, offset, &l2_table, &l2_index);
+        if (ret < 0) {
+            return ret;
+        }
+
+        /* For the moment, overwrite compressed clusters one by one */
+        uint64_t entry = be64_to_cpu(l2_table[l2_index + keep_clusters]);
+        if (entry & QCOW_OFLAG_COMPRESSED) {
+            nb_clusters = 1;
+        } else {
+            nb_clusters = count_cow_clusters(s, nb_clusters, l2_table,
+                                             l2_index + keep_clusters);
+        }
+
+        ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
+        if (ret < 0) {
+            return ret;
+        }
+
         /* Calculate start and size of allocation */
         alloc_offset = offset + keep_bytes;