blob: f9b59c26321906d9b7039fc977ebf80cbe8ca6b4
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 | } |
189 |