1 files changed, 33 insertions, 9 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index ee4530cdbd..9f1b6461c8 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1926,6 +1926,7 @@ static void qcow2_refresh_limits(BlockDriverState *bs, Error **errp)
 static int qcow2_reopen_prepare(BDRVReopenState *state,
                                 BlockReopenQueue *queue, Error **errp)
 {
+    BDRVQcow2State *s = state->bs->opaque;
     Qcow2ReopenState *r;
     int ret;
 
@@ -1956,6 +1957,16 @@ static int qcow2_reopen_prepare(BDRVReopenState *state,
         }
     }
 
+    /*
+     * Without an external data file, s->data_file points to the same BdrvChild
+     * as bs->file. It needs to be resynced after reopen because bs->file may
+     * be changed. We can't use it in the meantime.
+     */
+    if (!has_data_file(state->bs)) {
+        assert(s->data_file == state->bs->file);
+        s->data_file = NULL;
+    }
+
     return 0;
 
 fail:
@@ -1966,7 +1977,16 @@ fail:
 
 static void qcow2_reopen_commit(BDRVReopenState *state)
 {
+    BDRVQcow2State *s = state->bs->opaque;
+
     qcow2_update_options_commit(state->bs, state->opaque);
+    if (!s->data_file) {
+        /*
+         * If we don't have an external data file, s->data_file was cleared by
+         * qcow2_reopen_prepare() and needs to be updated.
+         */
+        s->data_file = state->bs->file;
+    }
     g_free(state->opaque);
 }
 
@@ -1990,6 +2010,15 @@ static void qcow2_reopen_commit_post(BDRVReopenState *state)
 
 static void qcow2_reopen_abort(BDRVReopenState *state)
 {
+    BDRVQcow2State *s = state->bs->opaque;
+
+    if (!s->data_file) {
+        /*
+         * If we don't have an external data file, s->data_file was cleared by
+         * qcow2_reopen_prepare() and needs to be restored.
+         */
+        s->data_file = state->bs->file;
+    }
     qcow2_update_options_abort(state->bs, state->opaque);
     g_free(state->opaque);
 }
@@ -5620,15 +5649,10 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
     if (backing_file || backing_format) {
         if (g_strcmp0(backing_file, s->image_backing_file) ||
             g_strcmp0(backing_format, s->image_backing_format)) {
-            warn_report("Deprecated use of amend to alter the backing file; "
-                        "use qemu-img rebase instead");
-        }
-        ret = qcow2_change_backing_file(bs,
-                    backing_file ?: s->image_backing_file,
-                    backing_format ?: s->image_backing_format);
-        if (ret < 0) {
-            error_setg_errno(errp, -ret, "Failed to change the backing file");
-            return ret;
+            error_setg(errp, "Cannot amend the backing file");
+            error_append_hint(errp,
+                              "You can use 'qemu-img rebase' instead.\n");
+            return -EINVAL;
         }
     }