qmp-commands: move 'change-backing-file' doc to schema

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/qmp-commands.txt

@@ -549,37 +549,6 @@ Example:
                                                   "sync": "full" } }
 <- { "return": {} }
 
-change-backing-file
--------------------
-Since: 2.1
-
-Change the backing file in the image file metadata.  This does not cause
-QEMU to reopen the image file to reparse the backing filename (it may,
-however, perform a reopen to change permissions from r/o -> r/w -> r/o,
-if needed). The new backing file string is written into the image file
-metadata, and the QEMU internal strings are updated.
-
-Arguments:
-
-- "image-node-name":    The name of the block driver state node of the
-                        image to modify.  The "device" is argument is used to
-                        verify "image-node-name" is in the chain described by
-                        "device".
-                        (json-string, optional)
-
-- "device":             The device name or node-name of the root node that owns
-                        image-node-name.
-                        (json-string)
-
-- "backing-file":       The string to write as the backing file.  This string is
-                        not validated, so care should be taken when specifying
-                        the string or the image chain may not be able to be
-                        reopened again.
-                        (json-string)
-
-Returns: Nothing on success
-         If "device" does not exist or cannot be determined, DeviceNotFound
-
 block_set_io_throttle
 ------------
 

qapi/block-core.json

@@ -1233,7 +1233,9 @@
 # updated.
 #
 # @image-node-name: The name of the block driver state node of the
-#                   image to modify.
+#                   image to modify. The "device" argument is used
+#                   to verify "image-node-name" is in the chain
+#                   described by "device".
 #
 # @device:          The device name or node-name of the root node that owns
 #                   image-node-name.
@@ -1243,6 +1245,10 @@
 #                   when specifying the string or the image chain may
 #                   not be able to be reopened again.
 #
+# Returns: Nothing on success
+#
+#          If "device" does not exist or cannot be determined, DeviceNotFound
+#
 # Since: 2.1
 ##
 { 'command': 'change-backing-file',