savevm: Delete existing snapshots in all images

When creating a snapshot we can run into the situation that the first disk
doesn't have a snapshot, but the second one does have one with the same name as
the new snapshot.

In this case, qemu doesn't recognize that there is a snapshot to be
overwritten, so it starts to save the new snapshot and errors out later when it
tries to snapshot the second image. With this patch, snapshots on secondary
images are overwritten just like on the first image.
Reported-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

savevm.c

@@ -1535,12 +1535,40 @@ static int bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
     return ret;
 }
 
+/*
+ * Deletes snapshots of a given name in all opened images.
+ */
+static int del_existing_snapshots(Monitor *mon, const char *name)
+{
+    BlockDriverState *bs;
+    DriveInfo *dinfo;
+    QEMUSnapshotInfo sn1, *snapshot = &sn1;
+    int ret;
+
+    QTAILQ_FOREACH(dinfo, &drives, next) {
+        bs = dinfo->bdrv;
+        if (bdrv_can_snapshot(bs) &&
+            bdrv_snapshot_find(bs, snapshot, name) >= 0)
+        {
+            ret = bdrv_snapshot_delete(bs, name);
+            if (ret < 0) {
+                monitor_printf(mon,
+                               "Error while deleting snapshot on '%s'\n",
+                               bdrv_get_device_name(bs));
+                return -1;
+            }
+        }
+    }
+
+    return 0;
+}
+
 void do_savevm(Monitor *mon, const QDict *qdict)
 {
     DriveInfo *dinfo;
     BlockDriverState *bs, *bs1;
     QEMUSnapshotInfo sn1, *sn = &sn1, old_sn1, *old_sn = &old_sn1;
-    int must_delete, ret;
+    int ret;
     QEMUFile *f;
     int saved_vm_running;
     uint32_t vm_state_size;
@@ -1563,20 +1591,15 @@ void do_savevm(Monitor *mon, const QDict *qdict)
     saved_vm_running = vm_running;
     vm_stop(0);
 
-    must_delete = 0;
+    memset(sn, 0, sizeof(*sn));
     if (name) {
         ret = bdrv_snapshot_find(bs, old_sn, name);
         if (ret >= 0) {
-            must_delete = 1;
-        }
-    }
-    memset(sn, 0, sizeof(*sn));
-    if (must_delete) {
-        pstrcpy(sn->name, sizeof(sn->name), old_sn->name);
-        pstrcpy(sn->id_str, sizeof(sn->id_str), old_sn->id_str);
-    } else {
-        if (name)
+            pstrcpy(sn->name, sizeof(sn->name), old_sn->name);
+            pstrcpy(sn->id_str, sizeof(sn->id_str), old_sn->id_str);
+        } else {
             pstrcpy(sn->name, sizeof(sn->name), name);
+        }
     }
 
     /* fill auxiliary fields */
@@ -1591,6 +1614,11 @@ void do_savevm(Monitor *mon, const QDict *qdict)
 #endif
     sn->vm_clock_nsec = qemu_get_clock(vm_clock);
 
+    /* Delete old snapshots of the same name */
+    if (del_existing_snapshots(mon, name) < 0) {
+        goto the_end;
+    }
+
     /* save the VM state */
     f = qemu_fopen_bdrv(bs, 1);
     if (!f) {
@@ -1610,14 +1638,6 @@ void do_savevm(Monitor *mon, const QDict *qdict)
     QTAILQ_FOREACH(dinfo, &drives, next) {
         bs1 = dinfo->bdrv;
         if (bdrv_has_snapshot(bs1)) {
-            if (must_delete) {
-                ret = bdrv_snapshot_delete(bs1, old_sn->id_str);
-                if (ret < 0) {
-                    monitor_printf(mon,
-                                   "Error while deleting snapshot on '%s'\n",
-                                   bdrv_get_device_name(bs1));
-                }
-            }
             /* Write VM state size only to the image that contains the state */
             sn->vm_state_size = (bs == bs1 ? vm_state_size : 0);
             ret = bdrv_snapshot_create(bs1, sn);