1 /* oneit.c - tiny init replacement to launch a single child process.
2 *
3 * Copyright 2005, 2007 by Rob Landley <rob@landley.net>.
4
5 USE_ONEIT(NEWTOY(oneit, "^<1nc:p3[!pn]", TOYFLAG_SBIN))
6
7 config ONEIT
8 bool "oneit"
9 default y
10 help
11 usage: oneit [-prn3] [-c CONSOLE] [COMMAND...]
12
13 Simple init program that runs a single supplied command line with a
14 controlling tty (so CTRL-C can kill it).
15
16 -c Which console device to use (/dev/console doesn't do CTRL-C, etc)
17 -p Power off instead of rebooting when command exits
18 -r Restart child when it exits
19 -n No reboot, just relaunch command line
20 -3 Write 32 bit PID of each exiting reparented process to fd 3 of child
21 (Blocking writes, child must read to avoid eventual deadlock.)
22
23 Spawns a single child process (because PID 1 has signals blocked)
24 in its own session, reaps zombies until the child exits, then
25 reboots the system (or powers off with -p, or restarts the child with -r).
26
27 Responds to SIGUSR1 by halting the system, SIGUSR2 by powering off,
28 and SIGTERM or SIGINT reboot.
29 */
30
31 #define FOR_oneit
32 #include "toys.h"
33 #include <sys/reboot.h>
34
GLOBALS(char * c;)35 GLOBALS(
36 char *c;
37 )
38
39 // The minimum amount of work necessary to get ctrl-c and such to work is:
40 //
41 // - Fork a child (PID 1 is special: can't exit, has various signals blocked).
42 // - Do a setsid() (so we have our own session).
43 // - In the child, attach stdio to TT.c (/dev/console is special)
44 // - Exec the rest of the command line.
45 //
46 // PID 1 then reaps zombies until the child process it spawned exits, at which
47 // point it calls sync() and reboot(). I could stick a kill -1 in there.
48
49 // Perform actions in response to signals. (Only root can send us signals.)
50 static void oneit_signaled(int signal)
51 {
52 int action = RB_AUTOBOOT;
53
54 toys.signal = signal;
55 if (signal == SIGUSR1) action = RB_HALT_SYSTEM;
56 if (signal == SIGUSR2) action = RB_POWER_OFF;
57
58 // PID 1 can't call reboot() because it kills the task that calls it,
59 // which causes the kernel to panic before the actual reboot happens.
60 sync();
61 if (getpid()!=1) _exit(127+signal);
62 if (!vfork()) reboot(action);
63 }
64
oneit_main(void)65 void oneit_main(void)
66 {
67 int i, pid, pipes[] = {SIGUSR1, SIGUSR2, SIGTERM, SIGINT};
68 char *ss = toybuf+5;
69
70 // Setup signal handlers for signals of interest
71 for (i = 0; i<ARRAY_LEN(pipes); i++) xsignal(pipes[i], oneit_signaled);
72
73 // Autodetect console from sysfs if no -c
74 memcpy(toybuf, "/dev/", 5);
75 i = sizeof(toybuf)-6;
76 if (!TT.c && (TT.c = readfile("/sys/class/tty/console/active", ss, i))) {
77 // Take last entry, remove newline terminator
78 while (TT.c[i = strcspn(TT.c, " \n")]) {
79 TT.c[i++] = 0;
80 if (TT.c[i]) TT.c += i;
81 else break;
82 }
83 // Ensure exactly one /dev prefix
84 strstart(&TT.c, "/dev/");
85 memmove(toybuf+5, TT.c, strlen(TT.c));
86 TT.c = toybuf;
87 }
88
89 // Redirect stdin/out/err. Remember, O_CLOEXEC is backwards for xopen()
90 close(0);
91 xopen_stdio(TT.c ? : "/dev/tty0", O_RDWR|O_CLOEXEC);
92 close(1);
93 dup(0);
94 close(2);
95 dup(0);
96
97 if (FLAG(3)) {
98 // Ensure next available filehandles are #3 and #4
99 close(3);
100 close(4);
101 xpipe(pipes);
102 fcntl(4, F_SETFD, FD_CLOEXEC);
103 }
104
105 while (!toys.signal) {
106
107 // Create a new child process.
108 pid = XVFORK();
109 if (pid) {
110
111 // pid 1 reaps zombies until it gets its child, then halts system.
112 // We ignore the return value of write (what would we do with it?)
113 // but save it in a variable we never read to make fortify shut up.
114 // (Real problem is if pid2 never reads, write() fills pipe and blocks.)
115 while (pid != wait(&i)) if (FLAG(3)) i = write(4, &pid, 4);
116 if (FLAG(n)) continue;
117
118 oneit_signaled(FLAG(p) ? SIGUSR2 : SIGTERM);
119 } else {
120 // new session ID in child, so ctrl-c works.
121 setsid();
122
123 // Can't xexec() here, we vforked so we don't want to error_exit().
124 toy_exec(toys.optargs);
125 execvp(*toys.optargs, toys.optargs);
126 perror_msg("%s not in PATH=%s", *toys.optargs, getenv("PATH"));
127
128 break;
129 }
130 }
131
132 // Give reboot() time to kick in, or avoid rapid spinning if exec failed
133 sleep(5);
134 _exit(127);
135 }
136