[Qemu-devel] [PATCH for-4.2 05/13] qcow2: Write v3-compliant snapshot list on upgrade

[Max Reitz <mreitz@redhat.com>]

qcow2 v3 requires every snapshot table entry to have two extra data
fields: The 64-bit VM state size, and the virtual disk size.  Both are
optional for v2 images, so they may not be present.

qcow2_upgrade() therefore should update the snapshot table to ensure all
entries have these extra data fields.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1727347
Reported-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 99e9dad798..75d41683a1 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -4731,7 +4731,9 @@ static int qcow2_upgrade(BlockDriverState *bs, int target_version,
                          Error **errp)
 {
     BDRVQcow2State *s = bs->opaque;
+    bool need_snapshot_update;
     int current_version = s->qcow_version;
+    int i;
     int ret;
 
     /* This is qcow2_upgrade(), not qcow2_downgrade() */
@@ -4740,7 +4742,30 @@ static int qcow2_upgrade(BlockDriverState *bs, int target_version,
     /* There are no other versions (yet) that you can upgrade to */
     assert(target_version == 3);
 
-    status_cb(bs, 0, 1, cb_opaque);
+    status_cb(bs, 0, 2, cb_opaque);
+
+    /*
+     * In v2, snapshots do not need to have extra data.  v3 requires
+     * the 64-bit VM state size and the virtual disk size to be
+     * present.
+     * qcow2_write_snapshots() will always write the list in the
+     * v3-compliant format.
+     */
+    need_snapshot_update = false;
+    for (i = 0; i < s->nb_snapshots; i++) {
+        if (s->snapshots[i].extra_data_size < 16) {
+            need_snapshot_update = true;
+            break;
+        }
+    }
+    if (need_snapshot_update) {
+        ret = qcow2_write_snapshots(bs);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to update the snapshot table");
+            return ret;
+        }
+    }
+    status_cb(bs, 1, 2, cb_opaque);
 
     s->qcow_version = target_version;
     ret = qcow2_update_header(bs);
@@ -4749,7 +4774,7 @@ static int qcow2_upgrade(BlockDriverState *bs, int target_version,
         error_setg_errno(errp, -ret, "Failed to update the image header");
         return ret;
     }
-    status_cb(bs, 1, 1, cb_opaque);
+    status_cb(bs, 2, 2, cb_opaque);
 
     return 0;
 }
-- 
2.21.0