chardev: add qmp hotplug commands, with null chardev support

Add chardev-add and chardev-remove qmp commands.  Hotplugging
a null chardev is supported for now, more will be added later.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

qmp-commands.hx

@@ -2654,3 +2654,53 @@ EQMP
         .args_type  = "",
         .mhandler.cmd_new = qmp_marshal_input_query_target,
     },
+
+    {
+        .name       = "chardev-add",
+        .args_type  = "id:s,backend:q",
+        .mhandler.cmd_new = qmp_marshal_input_chardev_add,
+    },
+
+SQMP
+chardev-add
+----------------
+
+Add a chardev.
+
+Arguments:
+
+- "id": the chardev's ID, must be unique (json-string)
+- "backend": chardev backend type + parameters
+
+Example:
+
+-> { "execute" : "chardev-add",
+     "arguments" : { "id" : "foo",
+                     "backend" : { "type" : "null", "data" : {} } } }
+<- { "return": {} }
+
+EQMP
+
+    {
+        .name       = "chardev-remove",
+        .args_type  = "id:s",
+        .mhandler.cmd_new = qmp_marshal_input_chardev_remove,
+    },
+
+
+SQMP
+chardev-remove
+--------------
+
+Remove a chardev.
+
+Arguments:
+
+- "id": the chardev's ID, must exist and not be in use (json-string)
+
+Example:
+
+-> { "execute": "chardev-remove", "arguments": { "id" : "foo" } }
+<- { "return": {} }
+
+EQMP