termios: Add IO control handler

Update #2785.

cpukit/libcsupport/include/rtems/termiostypes.h

@@ -183,6 +183,21 @@ typedef struct {
     const struct termios         *term
   );
 
+  /**
+   * @brief IO control handler.
+   *
+   * Invoked in case the Termios layer cannot deal with the IO request.
+   *
+   * @param[in] context The Termios device context.
+   * @param[in] request The IO control request.
+   * @param[in] buffer The IO control buffer.
+   */
+  int (*ioctl)(
+    rtems_termios_device_context *context,
+    ioctl_command_t               request,
+    void                         *buffer
+  );
+
   /**
    * @brief Termios device mode.
    */

cpukit/libcsupport/src/termios.c

@@ -781,8 +781,11 @@ rtems_termios_ioctl (void *arg)
   default:
     if (rtems_termios_linesw[tty->t_line].l_ioctl != NULL) {
       sc = rtems_termios_linesw[tty->t_line].l_ioctl(tty,args);
-    }
-    else {
+    } else if (tty->handler.ioctl) {
+      args->ioctl_return = (*tty->handler.ioctl) (tty->device_context,
+        args->command, args->buffer);
+      sc = RTEMS_SUCCESSFUL;
+    } else {
       sc = RTEMS_INVALID_NUMBER;
     }
     break;