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 //config:config CTTYHACK
8 //config: bool "cttyhack (2.4 kb)"
9 //config: default y
10 //config: help
11 //config: One common problem reported on the mailing list is the "can't
12 //config: access tty; job control turned off" error message, which typically
13 //config: appears when one tries to use a shell with stdin/stdout on
14 //config: /dev/console.
15 //config: This device is special - it cannot be a controlling tty.
16 //config:
17 //config: The proper solution is to use the correct device instead of
18 //config: /dev/console.
19 //config:
20 //config: cttyhack provides a "quick and dirty" solution to this problem.
21 //config: It analyzes stdin with various ioctls, trying to determine whether
22 //config: it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line).
23 //config: On Linux it also checks sysfs for a pointer to the active console.
24 //config: If cttyhack is able to find the real console device, it closes
25 //config: stdin/out/err and reopens that device.
26 //config: Then it executes the given program. Opening the device will make
27 //config: that device a controlling tty. This may require cttyhack
28 //config: to be a session leader.
29 //config:
30 //config: Example for /etc/inittab (for busybox init):
31 //config:
32 //config: ::respawn:/bin/cttyhack /bin/sh
33 //config:
34 //config: Starting an interactive shell from boot shell script:
35 //config:
36 //config: setsid cttyhack sh
37 //config:
38 //config: Giving controlling tty to shell running with PID 1:
39 //config:
40 //config: # exec cttyhack sh
41 //config:
42 //config: Without cttyhack, you need to know exact tty name,
43 //config: and do something like this:
44 //config:
45 //config: # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
46 //config:
47 //config: Starting getty on a controlling tty from a shell script:
48 //config:
49 //config: # getty 115200 $(cttyhack)
50
51 //applet:IF_CTTYHACK(APPLET_NOEXEC(cttyhack, cttyhack, BB_DIR_BIN, BB_SUID_DROP, cttyhack))
52
53 //kbuild:lib-$(CONFIG_CTTYHACK) += cttyhack.o
54
55 //usage:#define cttyhack_trivial_usage
56 //usage: "[PROG ARGS]"
57 //usage:#define cttyhack_full_usage "\n\n"
58 //usage: "Give PROG a controlling tty if possible."
59 //usage: "\nExample for /etc/inittab (for busybox init):"
60 //usage: "\n ::respawn:/bin/cttyhack /bin/sh"
61 //usage: "\nGiving controlling tty to shell running with PID 1:"
62 //usage: "\n $ exec cttyhack sh"
63 //usage: "\nStarting interactive shell from boot shell script:"
64 //usage: "\n setsid cttyhack sh"
65
66 #include "libbb.h"
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;
cttyhack_main(int argc UNUSED_PARAM,char ** argv)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 }
189