File: cttyhack.c

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/* vi: set sw=4 ts=4: */
/*
 * Licensed under GPLv2
 *
 * Copyright (c) 2007 Denys Vlasenko <vda.linux@googlemail.com>
 */
#include "libbb.h"

#if !defined(__linux__) && !defined(TIOCGSERIAL)
# 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);
}