commit 5a385bf5c5cb3069fab17c014cf4b4f629509f1e
author Eric Blake <eblake@redhat.com> Mon May 03 14:35:59 2021 -0700
committer Kevin Wolf <kwolf@redhat.com> Fri Jul 09 12:26:05 2021 +0200
tree 048c44a2cd42c4c0b3ac18a80a5be54620d5011e
parent 2842ff2d81ddd86b1d0dd3b98c46b72bfa5cb4cb

qcow2: Prohibit backing file changes in 'qemu-img amend'

This was deprecated back in bc5ee6da7 (qcow2: Deprecate use of
qemu-img amend to change backing file), and no one in the meantime has
given any reasons why it should be supported.  Time to make change
attempts a hard error (but for convenience, specifying the _same_
backing chain is not forbidden).  Update a couple of iotests to match.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210503213600.569128-2-eblake@redhat.com>
Reviewed-by: Connor Kuehl <ckuehl@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow2.c

diff --git a/block/qcow2.c b/block/qcow2.c
index ee4530c..0cac2ed 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -5620,15 +5620,10 @@
     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;
         }
     }