add example usage to hello command

include/grub/extcmd.h

@@ -21,10 +21,12 @@
 
 #include <grub/lib/arg.h>
 #include <grub/command.h>
+#include <grub/script_sh.h>
 
 struct grub_extcmd;
+struct grub_extcmd_context;
 
-typedef grub_err_t (*grub_extcmd_func_t) (struct grub_extcmd *cmd,
+typedef grub_err_t (*grub_extcmd_func_t) (struct grub_extcmd_context *ctxt,
 					  int argc, char **args);
 
 /* The argcmd description.  */
@@ -38,11 +40,21 @@ struct grub_extcmd
   const struct grub_arg_option *options;
 
   void *data;
-
-  struct grub_arg_list *state;
 };
 typedef struct grub_extcmd *grub_extcmd_t;
 
+/* Command context for each instance of execution.  */
+struct grub_extcmd_context
+{
+  struct grub_extcmd *extcmd;
+
+  struct grub_arg_list *state;
+
+  /* Script parameters, if any.  */
+  struct grub_script **script_params;
+};
+typedef struct grub_extcmd_context *grub_extcmd_context_t;
+
 grub_extcmd_t grub_register_extcmd (const char *name,
 				    grub_extcmd_func_t func,
 				    unsigned flags,
@@ -52,4 +64,8 @@ grub_extcmd_t grub_register_extcmd (const char *name,
 
 void grub_unregister_extcmd (grub_extcmd_t cmd);
 
+grub_err_t
+grub_extcmd_dispatcher (struct grub_command *cmd, int argc, char **args,
+			struct grub_script **scripts);
+
 #endif /* ! GRUB_EXTCMD_HEADER */