release/src/router/busybox/shell/cttyhack.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Copyright (c) 2007 Denys Vlasenko <vda.linux@googlemail.com>
   4  *
   5  * Licensed under GPLv2, see file LICENSE in this source tree.
   6  */
   7 #include "libbb.h"
   8
   9 //applet:IF_CTTYHACK(APPLET(cttyhack, BB_DIR_BIN, BB_SUID_DROP))
  10
  11 //kbuild:lib-$(CONFIG_CTTYHACK) += cttyhack.o
  12
  13 //config:config CTTYHACK
  14 //config:       bool "cttyhack"
  15 //config:       default y
  16 //config:       help
  17 //config:         One common problem reported on the mailing list is the "can't
  18 //config:         access tty; job control turned off" error message, which typically
  19 //config:         appears when one tries to use a shell with stdin/stdout on
  20 //config:         /dev/console.
  21 //config:         This device is special - it cannot be a controlling tty.
  22 //config:
  23 //config:         The proper solution is to use the correct device instead of
  24 //config:         /dev/console.
  25 //config:
  26 //config:         cttyhack provides a "quick and dirty" solution to this problem.
  27 //config:         It analyzes stdin with various ioctls, trying to determine whether
  28 //config:         it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line).
  29 //config:         On Linux it also checks sysfs for a pointer to the active console.
  30 //config:         If cttyhack is able to find the real console device, it closes
  31 //config:         stdin/out/err and reopens that device.
  32 //config:         Then it executes the given program. Opening the device will make
  33 //config:         that device a controlling tty. This may require cttyhack
  34 //config:         to be a session leader.
  35 //config:
  36 //config:         Example for /etc/inittab (for busybox init):
  37 //config:
  38 //config:         ::respawn:/bin/cttyhack /bin/sh
  39 //config:
  40 //config:         Starting an interactive shell from boot shell script:
  41 //config:
  42 //config:         setsid cttyhack sh
  43 //config:
  44 //config:         Giving controlling tty to shell running with PID 1:
  45 //config:
  46 //config:         # exec cttyhack sh
  47 //config:
  48 //config:         Without cttyhack, you need to know exact tty name,
  49 //config:         and do something like this:
  50 //config:
  51 //config:         # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
  52 //config:
  53 //config:         Starting getty on a controlling tty from a shell script:
  54 //config:
  55 //config:         # getty 115200 $(cttyhack)
  56
  57 //usage:#define cttyhack_trivial_usage
  58 //usage:       "[PROG ARGS]"
  59 //usage:#define cttyhack_full_usage "\n\n"
  60 //usage:       "Give PROG a controlling tty if possible."
  61 //usage:     "\nExample for /etc/inittab (for busybox init):"
  62 //usage:     "\n        ::respawn:/bin/cttyhack /bin/sh"
  63 //usage:     "\nGiving controlling tty to shell running with PID 1:"
  64 //usage:     "\n        $ exec cttyhack sh"
  65 //usage:     "\nStarting interactive shell from boot shell script:"
  66 //usage:     "\n        setsid cttyhack sh"
  67
  68 #if !defined(__linux__) && !defined(TIOCGSERIAL) && !ENABLE_WERROR
  69 # warning cttyhack will not be able to detect a controlling tty on this system
  70 #endif
  71
  72 /* From <linux/vt.h> */
  73 struct vt_stat {
  74         unsigned short v_active;        /* active vt */
  75         unsigned short v_signal;        /* signal to send */
  76         unsigned short v_state;         /* vt bitmask */
  77 };
  78 enum { VT_GETSTATE = 0x5603 }; /* get global vt state info */
  79
  80 /* From <linux/serial.h> */
  81 struct serial_struct {
  82         int     type;
  83         int     line;
  84         unsigned int    port;
  85         int     irq;
  86         int     flags;
  87         int     xmit_fifo_size;
  88         int     custom_divisor;
  89         int     baud_base;
  90         unsigned short  close_delay;
  91         char    io_type;
  92         char    reserved_char[1];
  93         int     hub6;
  94         unsigned short  closing_wait;   /* time to wait before closing */
  95         unsigned short  closing_wait2;  /* no longer used... */
  96         unsigned char   *iomem_base;
  97         unsigned short  iomem_reg_shift;
  98         unsigned int    port_high;
  99         unsigned long   iomap_base;     /* cookie passed into ioremap */
 100         int     reserved[1];
 101 };
 102
 103 int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 104 int cttyhack_main(int argc UNUSED_PARAM, char **argv)
 105 {
 106         int fd;
 107         char console[sizeof(int)*3 + 16];
 108         union {
 109                 struct vt_stat vt;
 110                 struct serial_struct sr;
 111                 char paranoia[sizeof(struct serial_struct) * 3];
 112         } u;
 113
 114         strcpy(console, "/dev/tty");
 115         fd = open(console, O_RDWR);
 116         if (fd < 0) {
 117                 /* We don't have ctty (or don't have "/dev/tty" node...) */
 118                 do {
 119 #ifdef __linux__
 120                         /* Note that this method does not use _stdin_.
 121                          * Thus, "cttyhack </dev/something" can't be used.
 122                          * However, this method is more reliable than
 123                          * TIOCGSERIAL check, which assumes that all
 124                          * serial lines follow /dev/ttySn convention -
 125                          * which is not always the case.
 126                          * Therefore, we use this method first:
 127                          */
 128                         int s = open_read_close("/sys/class/tty/console/active",
 129                                 console + 5, sizeof(console) - 5);
 130                         if (s > 0) {
 131                                 char *last;
 132                                 /* Found active console via sysfs (Linux 2.6.38+).
 133                                  * It looks like "[tty0 ]ttyS0\n" so zap the newline:
 134                                  */
 135                                 console[4 + s] = '\0';
 136                                 /* If there are multiple consoles,
 137                                  * take the last one:
 138                                  */
 139                                 last = strrchr(console + 5, ' ');
 140                                 if (last)
 141                                         overlapping_strcpy(console + 5, last + 1);
 142                                 break;
 143                         }
 144
 145                         if (ioctl(0, VT_GETSTATE, &u.vt) == 0) {
 146                                 /* this is linux virtual tty */
 147                                 sprintf(console + 8, "S%u" + 1, (int)u.vt.v_active);
 148                                 break;
 149                         }
 150 #endif
 151 #ifdef TIOCGSERIAL
 152                         if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) {
 153                                 /* this is a serial console; assuming it is named /dev/ttySn */
 154                                 sprintf(console + 8, "S%u", (int)u.sr.line);
 155                                 break;
 156                         }
 157 #endif
 158                         /* nope, could not find it */
 159                         console[0] = '\0';
 160                 } while (0);
 161         }
 162
 163         argv++;
 164         if (!argv[0]) {
 165                 if (!console[0])
 166                         return EXIT_FAILURE;
 167                 puts(console);
 168                 return EXIT_SUCCESS;
 169         }
 170
 171         if (fd < 0) {
 172                 fd = open_or_warn(console, O_RDWR);
 173                 if (fd < 0)
 174                         goto ret;
 175         }
 176         //bb_error_msg("switching to '%s'", console);
 177         dup2(fd, 0);
 178         dup2(fd, 1);
 179         dup2(fd, 2);
 180         while (fd > 2)
 181                 close(fd--);
 182         /* Some other session may have it as ctty,
 183          * try to steal it from them:
 184          */
 185         ioctl(0, TIOCSCTTY, 1);
 186  ret:
 187         BB_EXECVP_or_die(argv);
 188 }