text: /* vi: set sw=4 ts=4: */
  /*
   * mesg implementation for busybox
   *
   * Copyright (c) 2002 Manuel Novoa III  <mjn3@codepoet.org>
   *
   * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   */
  //config:config MESG
  //config:	bool "mesg (1.2 kb)"
  //config:	default y
  //config:	help
  //config:	Mesg controls access to your terminal by others. It is typically
  //config:	used to allow or disallow other users to write to your terminal
  //config:
  //config:config FEATURE_MESG_ENABLE_ONLY_GROUP
  //config:	bool "Enable writing to tty only by group, not by everybody"
  //config:	default y
  //config:	depends on MESG
  //config:	help
  //config:	Usually, ttys are owned by group "tty", and "write" tool is
  //config:	setgid to this group. This way, "mesg y" only needs to enable
  //config:	"write by owning group" bit in tty mode.
  //config:
  //config:	If you set this option to N, "mesg y" will enable writing
  //config:	by anybody at all. This is not recommended.
  
  //applet:IF_MESG(APPLET_NOFORK(mesg, mesg, BB_DIR_USR_BIN, BB_SUID_DROP, mesg))
  
  //kbuild:lib-$(CONFIG_MESG) += mesg.o
  
  //usage:#define mesg_trivial_usage
  //usage:       "[y|n]"
  //usage:#define mesg_full_usage "\n\n"
  //usage:       "Control write access to your terminal\n"
  //usage:       "	y	Allow write access to your terminal\n"
  //usage:       "	n	Disallow write access to your terminal"
  
  #include "libbb.h"
  
  #if ENABLE_FEATURE_MESG_ENABLE_ONLY_GROUP
  #define S_IWGRP_OR_S_IWOTH  S_IWGRP
  #else
  #define S_IWGRP_OR_S_IWOTH  (S_IWGRP | S_IWOTH)
  #endif
  
  int mesg_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  int mesg_main(int argc UNUSED_PARAM, char **argv)
  {
  	struct stat sb;
  	mode_t m;
  	char c = 0;
  
  	argv++;
  
  	if (argv[0]
  	 && (argv[1] || ((c = argv[0][0]) != 'y' && c != 'n'))
  	) {
  		bb_show_usage();
  	}
  
  	/* We are a NOFORK applet.
  	 * (Not that it's very useful, but code is trivially NOFORK-safe).
  	 * Play nice. Do not leak anything.
  	 */
  
  	if (!isatty(STDIN_FILENO))
  		bb_error_msg_and_die("not a tty");
  
  	xfstat(STDIN_FILENO, &sb, "stdin");
  	if (c == 0) {
  		puts((sb.st_mode & (S_IWGRP|S_IWOTH)) ? "is y" : "is n");
  		return EXIT_SUCCESS;
  	}
  	m = (c == 'y') ? sb.st_mode | S_IWGRP_OR_S_IWOTH
  	               : sb.st_mode & ~(S_IWGRP|S_IWOTH);
  	if (fchmod(STDIN_FILENO, m) != 0)
  		bb_perror_nomsg_and_die();
  	return EXIT_SUCCESS;
  }
  