qemu: snapshot: Properly handle image locking

Images that became the backing chain of the current image due to the
snapshot need to be unlocked in the lock manager. Also if qemu was
paused during the snapshot the current top level images need to be
released until qemu is resumed so that they can be acquired properly.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1191901

src/qemu/qemu_driver.c

@@ -14486,6 +14486,23 @@ qemuDomainSnapshotCreateDiskActive(virQEMUDriverPtr driver,
                 virStorageFileUnlink(diskdata[i].src) < 0)
                 VIR_WARN("Unable to remove just-created %s", diskdata[i].src->path);
         }
+    } else {
+        /* on successful snapshot we need to remove locks from the now-old
+         * disks and if the VM is paused release locks on the images since qemu
+         * stopped using them*/
+        bool paused = virDomainObjGetState(vm, NULL) != VIR_DOMAIN_RUNNING;
+
+        for (i = 0; i < snap->def->ndisks; i++) {
+            if (!diskdata[i].disk)
+                continue;
+
+            if (paused)
+                virDomainLockImageDetach(driver->lockManager, vm,
+                                         diskdata[i].disk->src);
+
+            virDomainLockImageDetach(driver->lockManager, vm,
+                                     diskdata[i].disk->src->backingStore);
+        }
     }
 
     if (ret == 0 || !actions) {