[Qemu-devel] [PATCH] qcow2-refcount: Snapshot update for zero clusters

[Max Reitz <mreitz@redhat.com>]

Do not try to update the refcount for zero clusters in
qcow2_update_snapshot_refcount.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2-refcount.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 1244693..7555242 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -863,9 +863,13 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
             for(j = 0; j < s->l2_size; j++) {
                 offset = be64_to_cpu(l2_table[j]);
                 if (offset != 0) {
+                    uint64_t cluster_index;
+
                     old_offset = offset;
                     offset &= ~QCOW_OFLAG_COPIED;
-                    if (offset & QCOW_OFLAG_COMPRESSED) {
+
+                    switch (qcow2_get_cluster_type(offset)) {
+                    case QCOW2_CLUSTER_COMPRESSED:
                         nb_csectors = ((offset >> s->csize_shift) &
                                        s->csize_mask) + 1;
                         if (addend != 0) {
@@ -880,8 +884,10 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
                         }
                         /* compressed clusters are never modified */
                         refcount = 2;
-                    } else {
-                        uint64_t cluster_index = (offset & L2E_OFFSET_MASK) >> s->cluster_bits;
+                        break;
+
+                    case QCOW2_CLUSTER_NORMAL:
+                        cluster_index = (offset & L2E_OFFSET_MASK) >> s->cluster_bits;
                         if (addend != 0) {
                             refcount = update_cluster_refcount(bs, cluster_index, addend,
                                                                QCOW2_DISCARD_SNAPSHOT);
@@ -893,6 +899,10 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
                             ret = refcount;
                             goto fail;
                         }
+                        break;
+
+                    default:
+                        refcount = 0;
                     }
 
                     if (refcount == 1) {
-- 
1.8.3.1