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

Last change on this file was 3232, checked in by bruno, 5 years ago
  • Update mindi-busybox to 1.21.1
  • Property svn:eol-style set to native
File size: 5.6 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 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> */
73struct 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};
78enum { VT_GETSTATE = 0x5603 }; /* get global vt state info */
79
80/* From <linux/serial.h> */
81struct 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
103int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
104int 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}
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