source: branches/3.2/mindi-busybox/shell/cttyhack.c @ 3186

Last change on this file since 3186 was 2725, checked in by bruno, 8 years ago
  • Update mindi-busybox to 1.18.3 to avoid problems with the tar command which is now failing on recent versions with busybox 1.7.3
  • Property svn:eol-style set to native
File size: 4.4 KB
Line 
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 "can't access tty;
18//config:     job control turned off" error message which typically appears when
19//config:     one tries to use shell with stdin/stdout opened to /dev/console.
20//config:     This device is special - it cannot be a controlling tty.
21//config:
22//config:     Proper solution is to use correct device instead of /dev/console.
23//config:
24//config:     cttyhack provides "quick and dirty" solution to this problem.
25//config:     It analyzes stdin with various ioctls, trying to determine whether
26//config:     it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line).
27//config:     If it detects one, it closes stdin/out/err and reopens that device.
28//config:     Then it executes given program. Opening the device will make
29//config:     that device a controlling tty. This may require cttyhack
30//config:     to be a session leader.
31//config:
32//config:     Example for /etc/inittab (for busybox init):
33//config:
34//config:     ::respawn:/bin/cttyhack /bin/sh
35//config:
36//config:     Starting an interactive shell from boot shell script:
37//config:
38//config:     setsid cttyhack sh
39//config:
40//config:     Giving controlling tty to shell running with PID 1:
41//config:
42//config:     # exec cttyhack sh
43//config:
44//config:     Without cttyhack, you need to know exact tty name,
45//config:     and do something like this:
46//config:
47//config:     # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
48//config:
49
50//usage:#define cttyhack_trivial_usage
51//usage:       "PROG ARGS"
52//usage:#define cttyhack_full_usage "\n\n"
53//usage:       "Give PROG a controlling tty if possible."
54//usage:     "\nExample for /etc/inittab (for busybox init):"
55//usage:     "\n    ::respawn:/bin/cttyhack /bin/sh"
56//usage:     "\nGiving controlling tty to shell running with PID 1:"
57//usage:     "\n    $ exec cttyhack sh"
58//usage:     "\nStarting interactive shell from boot shell script:"
59//usage:     "\n    setsid cttyhack sh"
60
61#if !defined(__linux__) && !defined(TIOCGSERIAL) && !ENABLE_WERROR
62# warning cttyhack will not be able to detect a controlling tty on this system
63#endif
64
65/* From <linux/vt.h> */
66struct vt_stat {
67    unsigned short v_active;        /* active vt */
68    unsigned short v_signal;        /* signal to send */
69    unsigned short v_state;         /* vt bitmask */
70};
71enum { VT_GETSTATE = 0x5603 }; /* get global vt state info */
72
73/* From <linux/serial.h> */
74struct serial_struct {
75    int type;
76    int line;
77    unsigned int    port;
78    int irq;
79    int flags;
80    int xmit_fifo_size;
81    int custom_divisor;
82    int baud_base;
83    unsigned short  close_delay;
84    char    io_type;
85    char    reserved_char[1];
86    int hub6;
87    unsigned short  closing_wait;   /* time to wait before closing */
88    unsigned short  closing_wait2;  /* no longer used... */
89    unsigned char   *iomem_base;
90    unsigned short  iomem_reg_shift;
91    unsigned int    port_high;
92    unsigned long   iomap_base; /* cookie passed into ioremap */
93    int reserved[1];
94};
95
96int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
97int cttyhack_main(int argc UNUSED_PARAM, char **argv)
98{
99    int fd;
100    char console[sizeof(int)*3 + 16];
101    union {
102        struct vt_stat vt;
103        struct serial_struct sr;
104        char paranoia[sizeof(struct serial_struct) * 3];
105    } u;
106
107    if (!*++argv) {
108        bb_show_usage();
109    }
110
111    strcpy(console, "/dev/tty");
112    fd = open(console, O_RDWR);
113    if (fd >= 0) {
114        /* We already have ctty, nothing to do */
115        close(fd);
116    } else {
117        /* We don't have ctty (or don't have "/dev/tty" node...) */
118        if (0) {}
119#ifdef TIOCGSERIAL
120        else if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) {
121            /* this is a serial console */
122            sprintf(console + 8, "S%d", u.sr.line);
123        }
124#endif
125#ifdef __linux__
126        else if (ioctl(0, VT_GETSTATE, &u.vt) == 0) {
127            /* this is linux virtual tty */
128            sprintf(console + 8, "S%d" + 1, u.vt.v_active);
129        }
130#endif
131        if (console[8]) {
132            fd = xopen(console, O_RDWR);
133            //bb_error_msg("switching to '%s'", console);
134            dup2(fd, 0);
135            dup2(fd, 1);
136            dup2(fd, 2);
137            while (fd > 2)
138                close(fd--);
139            /* Some other session may have it as ctty,
140             * steal it from them:
141             */
142            ioctl(0, TIOCSCTTY, 1);
143        }
144    }
145
146    BB_EXECVP_or_die(argv);
147}
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