commit 4fbe5233fdaae22b96f9cd5a70351429fa91cce1
author Kevin Wolf <kwolf@redhat.com> Fri Aug 05 12:06:11 2011 +0200
committer Anthony Liguori <aliguori@us.ibm.com> Fri Aug 05 07:25:45 2011 -0500
tree c25af7be12c85d37c1bf8391fb74cab66b03c278
parent e2f775205a3523751ac479ec3194eb054376419d

qcow2: Fix L1 table size after bdrv_snapshot_goto

When loading an internal snapshot whose L1 table is smaller than the current L1
table, the size of the current L1 would be shrunk to the snapshot's L1 size in
memory, but not on disk. This lead to incorrect refcount updates and eventuelly
to image corruption.

Instead of writing the new L1 size to disk, this simply retains the bigger L1
size that is currently in use and makes sure that the unused part is zeroed.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Tested-by: Philipp Hahn <hahn@univention.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
(cherry picked from commit 35d7ace74bd07e3d6983c1fd7cbfab4e11175689)

block/qcow2-snapshot.c

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 74823a5..e32bcf0 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -317,7 +317,8 @@
 {
     BDRVQcowState *s = bs->opaque;
     QCowSnapshot *sn;
-    int i, snapshot_index, l1_size2;
+    int i, snapshot_index;
+    int cur_l1_bytes, sn_l1_bytes;
 
     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
     if (snapshot_index < 0)
@@ -330,14 +331,19 @@
     if (qcow2_grow_l1_table(bs, sn->l1_size, true) < 0)
         goto fail;
 
-    s->l1_size = sn->l1_size;
-    l1_size2 = s->l1_size * sizeof(uint64_t);
+    cur_l1_bytes = s->l1_size * sizeof(uint64_t);
+    sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
+
+    if (cur_l1_bytes > sn_l1_bytes) {
+        memset(s->l1_table + sn->l1_size, 0, cur_l1_bytes - sn_l1_bytes);
+    }
+
     /* copy the snapshot l1 table to the current l1 table */
     if (bdrv_pread(bs->file, sn->l1_table_offset,
-                   s->l1_table, l1_size2) != l1_size2)
+                   s->l1_table, sn_l1_bytes) < 0)
         goto fail;
     if (bdrv_pwrite_sync(bs->file, s->l1_table_offset,
-                    s->l1_table, l1_size2) < 0)
+                    s->l1_table, cur_l1_bytes) < 0)
         goto fail;
     for(i = 0;i < s->l1_size; i++) {
         be64_to_cpus(&s->l1_table[i]);