[Qemu-devel] [PATCH] qcow2: release refcount table clusters of the old table, after growing the refcount table

[Juergen Keil]

Another patch for qcow2:  when the refcount table is grown, clusters for 
the new refcount table are allocated, but the clusters for the old
(now unused) refcount table are not released.

This isn't a big problem, it just wastes a few clusters.

But it results in error messages when block-qcow2.c is compiled with
DEBUG_ALLOC / DEBUG_ALLOC2 error checking, and a qcow2 image has ever
grown the refcount table:


    /* compare ref counts */
    for(i = 0; i < nb_clusters; i++) {
        refcount1 = get_refcount(bs, i);
        refcount2 = refcount_table[i];
        if (refcount1 != refcount2)
            printf("ERROR cluster %d refcount=%d reference=%d\n",
                   i, refcount1, refcount2);
    }


% qemu-img info sol11-b60.img
ERROR cluster 9 refcount=1 reference=0            <<<<<<<<<<<<<<<<<<<<<<<<<<<
image: sol11-b60.img
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 2.6G
cluster_size: 4096

Index: block-qcow2.c
===================================================================
RCS file: /cvsroot/qemu/qemu/block-qcow2.c,v
retrieving revision 1.5
diff -u -B -r1.5 block-qcow2.c
--- block-qcow2.c       1 Apr 2007 19:01:40 -0000       1.5
+++ block-qcow2.c       2 Apr 2007 10:17:54 -0000
@@ -1886,6 +1894,8 @@
     int64_t table_offset;
     uint64_t data64;
     uint32_t data32;
+    int old_table_size;
+    int64_t old_table_offset;
 
     if (min_size <= s->refcount_table_size)
         return 0;
@@ -1931,11 +1941,14 @@
                     &data32, sizeof(data32)) != sizeof(data32))
         goto fail;
     qemu_free(s->refcount_table);
+    old_table_offset = s->refcount_table_offset;
+    old_table_size = s->refcount_table_size;
     s->refcount_table = new_table;
     s->refcount_table_size = new_table_size;
     s->refcount_table_offset = table_offset;
 
     update_refcount(bs, table_offset, new_table_size2, 1);
+    free_clusters(bs, old_table_offset, old_table_size * sizeof(uint64_t));
     return 0;
  fail:
     free_clusters(bs, table_offset, new_table_size2);