text: /* vi: set sw=4 ts=4: */
  /*
   * Copyright (c) 2007 Denys Vlasenko <vda.linux@googlemail.com>
   *
   * Licensed under GPLv2, see file LICENSE in this source tree.
   */
  #include "libbb.h"
  
  //applet:IF_CTTYHACK(APPLET(cttyhack, _BB_DIR_BIN, _BB_SUID_DROP))
  
  //kbuild:lib-$(CONFIG_CTTYHACK) += cttyhack.o
  
  //config:config CTTYHACK
  //config:	bool "cttyhack"
  //config:	default y
  //config:	help
  //config:	  One common problem reported on the mailing list is "can't access tty;
  //config:	  job control turned off" error message which typically appears when
  //config:	  one tries to use shell with stdin/stdout opened to /dev/console.
  //config:	  This device is special - it cannot be a controlling tty.
  //config:
  //config:	  Proper solution is to use correct device instead of /dev/console.
  //config:
  //config:	  cttyhack provides "quick and dirty" solution to this problem.
  //config:	  It analyzes stdin with various ioctls, trying to determine whether
  //config:	  it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line).
  //config:	  If it detects one, it closes stdin/out/err and reopens that device.
  //config:	  Then it executes given program. Opening the device will make
  //config:	  that device a controlling tty. This may require cttyhack
  //config:	  to be a session leader.
  //config:
  //config:	  Example for /etc/inittab (for busybox init):
  //config:
  //config:	  ::respawn:/bin/cttyhack /bin/sh
  //config:
  //config:	  Starting an interactive shell from boot shell script:
  //config:
  //config:	  setsid cttyhack sh
  //config:
  //config:	  Giving controlling tty to shell running with PID 1:
  //config:
  //config:	  # exec cttyhack sh
  //config:
  //config:	  Without cttyhack, you need to know exact tty name,
  //config:	  and do something like this:
  //config:
  //config:	  # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
  //config:
  
  //usage:#define cttyhack_trivial_usage
  //usage:       "PROG ARGS"
  //usage:#define cttyhack_full_usage "\n\n"
  //usage:       "Give PROG a controlling tty if possible."
  //usage:     "\nExample for /etc/inittab (for busybox init):"
  //usage:     "\n	::respawn:/bin/cttyhack /bin/sh"
  //usage:     "\nGiving controlling tty to shell running with PID 1:"
  //usage:     "\n	$ exec cttyhack sh"
  //usage:     "\nStarting interactive shell from boot shell script:"
  //usage:     "\n	setsid cttyhack sh"
  
  #if !defined(__linux__) && !defined(TIOCGSERIAL) && !ENABLE_WERROR
  # warning cttyhack will not be able to detect a controlling tty on this system
  #endif
  
  /* From <linux/vt.h> */
  struct vt_stat {
  	unsigned short v_active;        /* active vt */
  	unsigned short v_signal;        /* signal to send */
  	unsigned short v_state;         /* vt bitmask */
  };
  enum { VT_GETSTATE = 0x5603 }; /* get global vt state info */
  
  /* From <linux/serial.h> */
  struct serial_struct {
  	int	type;
  	int	line;
  	unsigned int	port;
  	int	irq;
  	int	flags;
  	int	xmit_fifo_size;
  	int	custom_divisor;
  	int	baud_base;
  	unsigned short	close_delay;
  	char	io_type;
  	char	reserved_char[1];
  	int	hub6;
  	unsigned short	closing_wait;   /* time to wait before closing */
  	unsigned short	closing_wait2;  /* no longer used... */
  	unsigned char	*iomem_base;
  	unsigned short	iomem_reg_shift;
  	unsigned int	port_high;
  	unsigned long	iomap_base;	/* cookie passed into ioremap */
  	int	reserved[1];
  };
  
  int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  int cttyhack_main(int argc UNUSED_PARAM, char **argv)
  {
  	int fd;
  	char console[sizeof(int)*3 + 16];
  	union {
  		struct vt_stat vt;
  		struct serial_struct sr;
  		char paranoia[sizeof(struct serial_struct) * 3];
  	} u;
  
  	if (!*++argv) {
  		bb_show_usage();
  	}
  
  	strcpy(console, "/dev/tty");
  	fd = open(console, O_RDWR);
  	if (fd >= 0) {
  		/* We already have ctty, nothing to do */
  		close(fd);
  	} else {
  		/* We don't have ctty (or don't have "/dev/tty" node...) */
  		if (0) {}
  #ifdef TIOCGSERIAL
  		else if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) {
  			/* this is a serial console */
  			sprintf(console + 8, "S%d", u.sr.line);
  		}
  #endif
  #ifdef __linux__
  		else if (ioctl(0, VT_GETSTATE, &u.vt) == 0) {
  			/* this is linux virtual tty */
  			sprintf(console + 8, "S%d" + 1, u.vt.v_active);
  		}
  #endif
  		if (console[8]) {
  			fd = xopen(console, O_RDWR);
  			//bb_error_msg("switching to '%s'", console);
  			dup2(fd, 0);
  			dup2(fd, 1);
  			dup2(fd, 2);
  			while (fd > 2)
  				close(fd--);
  			/* Some other session may have it as ctty,
  			 * steal it from them:
  			 */
  			ioctl(0, TIOCSCTTY, 1);
  		}
  	}
  
  	BB_EXECVP_or_die(argv);
  }
  