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 [-p] [-c /dev/tty0] 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 -3 Write 32 bit PID of each exiting reparented process to fd 3 of child.
20 (Blocking writes, child must read to avoid eventual deadlock.)
21
22 Spawns a single child process (because PID 1 has signals blocked)
23 in its own session, reaps zombies until the child exits, then
24 reboots the system (or powers off with -p, or restarts the child with -r).
25 */
26
27 #define FOR_oneit
28 #include "toys.h"
29 #include <sys/reboot.h>
30
GLOBALS(char * console;)31 GLOBALS(
32 char *console;
33 )
34
35 // The minimum amount of work necessary to get ctrl-c and such to work is:
36 //
37 // - Fork a child (PID 1 is special: can't exit, has various signals blocked).
38 // - Do a setsid() (so we have our own session).
39 // - In the child, attach stdio to /dev/tty0 (/dev/console is special)
40 // - Exec the rest of the command line.
41 //
42 // PID 1 then reaps zombies until the child process it spawned exits, at which
43 // point it calls sync() and reboot(). I could stick a kill -1 in there.
44
45 // Perform actions in response to signals. (Only root can send us signals.)
46 static void oneit_signaled(int signal)
47 {
48 int action = RB_AUTOBOOT;
49
50 toys.signal = signal;
51 if (signal == SIGUSR1) action = RB_HALT_SYSTEM;
52 if (signal == SIGUSR2) action = RB_POWER_OFF;
53
54 // PID 1 can't call reboot() because it kills the task that calls it,
55 // which causes the kernel to panic before the actual reboot happens.
56 sync();
57 if (!vfork()) reboot(action);
58 }
59
oneit_main(void)60 void oneit_main(void)
61 {
62 int i, pid, pipes[] = {SIGUSR1, SIGUSR2, SIGTERM, SIGINT};
63
64 if (FLAG_3) {
65 // Ensure next available filehandle is #3
66 while (open("/", 0) < 3);
67 close(3);
68 close(4);
69 if (pipe(pipes)) perror_exit("pipe");
70 fcntl(4, F_SETFD, FD_CLOEXEC);
71 }
72
73 // Setup signal handlers for signals of interest
74 for (i = 0; i<ARRAY_LEN(pipes); i++) xsignal(pipes[i], oneit_signaled);
75
76 while (!toys.signal) {
77
78 // Create a new child process.
79 pid = vfork();
80 if (pid) {
81
82 // pid 1 reaps zombies until it gets its child, then halts system.
83 // We ignore the return value of write (what would we do with it?)
84 // but save it in a variable we never read to make fortify shut up.
85 // (Real problem is if pid2 never reads, write() fills pipe and blocks.)
86 while (pid != wait(&i)) if (FLAG_3) i = write(4, &pid, 4);
87 if (toys.optflags & FLAG_n) continue;
88
89 oneit_signaled((toys.optflags & FLAG_p) ? SIGUSR2 : SIGTERM);
90 } else {
91 // Redirect stdio to /dev/tty0, with new session ID, so ctrl-c works.
92 setsid();
93 for (i=0; i<3; i++) {
94 close(i);
95 // Remember, O_CLOEXEC is backwards for xopen()
96 xopen(TT.console ? TT.console : "/dev/tty0", O_RDWR|O_CLOEXEC);
97 }
98
99 // Can't xexec() here, we vforked so we don't want to error_exit().
100 toy_exec(toys.optargs);
101 execvp(*toys.optargs, toys.optargs);
102 perror_msg("%s not in PATH=%s", *toys.optargs, getenv("PATH"));
103
104 break;
105 }
106 }
107
108 // Give reboot() time to kick in, or avoid rapid spinning if exec failed
109 sleep(5);
110 _exit(127);
111 }
112