1/* oneit.c - tiny init replacement to launch a single child process. 2 * 3 * Copyright 2005, 2007 by Rob Landley <rob@landley.net>. 4 5USE_ONEIT(NEWTOY(oneit, "^<1nc:p3[!pn]", TOYFLAG_SBIN)) 6 7config 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 Responds to SIGUSR1 by halting the system, SIGUSR2 by powering off, 27 and SIGTERM or SIGINT reboot. 28*/ 29 30#define FOR_oneit 31#include "toys.h" 32#include <sys/reboot.h> 33 34GLOBALS( 35 char *c; 36) 37 38// The minimum amount of work necessary to get ctrl-c and such to work is: 39// 40// - Fork a child (PID 1 is special: can't exit, has various signals blocked). 41// - Do a setsid() (so we have our own session). 42// - In the child, attach stdio to /dev/tty0 (/dev/console is special) 43// - Exec the rest of the command line. 44// 45// PID 1 then reaps zombies until the child process it spawned exits, at which 46// point it calls sync() and reboot(). I could stick a kill -1 in there. 47 48// Perform actions in response to signals. (Only root can send us signals.) 49static void oneit_signaled(int signal) 50{ 51 int action = RB_AUTOBOOT; 52 53 toys.signal = signal; 54 if (signal == SIGUSR1) action = RB_HALT_SYSTEM; 55 if (signal == SIGUSR2) action = RB_POWER_OFF; 56 57 // PID 1 can't call reboot() because it kills the task that calls it, 58 // which causes the kernel to panic before the actual reboot happens. 59 sync(); 60 if (getpid()!=1) _exit(127+signal); 61 if (!vfork()) reboot(action); 62} 63 64void oneit_main(void) 65{ 66 int i, pid, pipes[] = {SIGUSR1, SIGUSR2, SIGTERM, SIGINT}; 67 68 // Setup signal handlers for signals of interest 69 for (i = 0; i<ARRAY_LEN(pipes); i++) xsignal(pipes[i], oneit_signaled); 70 71 if (FLAG(3)) { 72 // Ensure next available filehandles are #3 and #4 73 while (xopen_stdio("/", 0) < 3); 74 close(3); 75 close(4); 76 xpipe(pipes); 77 fcntl(4, F_SETFD, FD_CLOEXEC); 78 } 79 80 while (!toys.signal) { 81 82 // Create a new child process. 83 pid = XVFORK(); 84 if (pid) { 85 86 // pid 1 reaps zombies until it gets its child, then halts system. 87 // We ignore the return value of write (what would we do with it?) 88 // but save it in a variable we never read to make fortify shut up. 89 // (Real problem is if pid2 never reads, write() fills pipe and blocks.) 90 while (pid != wait(&i)) if (FLAG(3)) i = write(4, &pid, 4); 91 if (FLAG(n)) continue; 92 93 oneit_signaled(FLAG(p) ? SIGUSR2 : SIGTERM); 94 } else { 95 // Redirect stdio to /dev/tty0, with new session ID, so ctrl-c works. 96 setsid(); 97 for (i=0; i<3; i++) { 98 close(i); 99 // Remember, O_CLOEXEC is backwards for xopen() 100 xopen_stdio(TT.c ? TT.c : "/dev/tty0", O_RDWR|O_CLOEXEC); 101 } 102 103 // Can't xexec() here, we vforked so we don't want to error_exit(). 104 toy_exec(toys.optargs); 105 execvp(*toys.optargs, toys.optargs); 106 perror_msg("%s not in PATH=%s", *toys.optargs, getenv("PATH")); 107 108 break; 109 } 110 } 111 112 // Give reboot() time to kick in, or avoid rapid spinning if exec failed 113 sleep(5); 114 _exit(127); 115} 116