source: MondoRescue/branches/2.2.9/mindi-busybox/shell/cttyhack.c

/* 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);
}