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- /* oneit.c - tiny init replacement to launch a single child process.
- *
- * Copyright 2005, 2007 by Rob Landley <rob@landley.net>.
- USE_ONEIT(NEWTOY(oneit, "^<1nc:p3[!pn]", TOYFLAG_SBIN))
- config ONEIT
- bool "oneit"
- default y
- help
- usage: oneit [-prn3] [-c CONSOLE] [COMMAND...]
- Simple init program that runs a single supplied command line with a
- controlling tty (so CTRL-C can kill it).
- -c Which console device to use (/dev/console doesn't do CTRL-C, etc)
- -p Power off instead of rebooting when command exits
- -r Restart child when it exits
- -n No reboot, just relaunch command line
- -3 Write 32 bit PID of each exiting reparented process to fd 3 of child
- (Blocking writes, child must read to avoid eventual deadlock.)
- Spawns a single child process (because PID 1 has signals blocked)
- in its own session, reaps zombies until the child exits, then
- reboots the system (or powers off with -p, or restarts the child with -r).
- Responds to SIGUSR1 by halting the system, SIGUSR2 by powering off,
- and SIGTERM or SIGINT reboot.
- */
- #define FOR_oneit
- #include "toys.h"
- #include <sys/reboot.h>
- GLOBALS(
- char *c;
- )
- // The minimum amount of work necessary to get ctrl-c and such to work is:
- //
- // - Fork a child (PID 1 is special: can't exit, has various signals blocked).
- // - Do a setsid() (so we have our own session).
- // - In the child, attach stdio to TT.c (/dev/console is special)
- // - Exec the rest of the command line.
- //
- // PID 1 then reaps zombies until the child process it spawned exits, at which
- // point it calls sync() and reboot(). I could stick a kill -1 in there.
- // Perform actions in response to signals. (Only root can send us signals.)
- static void oneit_signaled(int signal)
- {
- int action = RB_AUTOBOOT;
- toys.signal = signal;
- if (signal == SIGUSR1) action = RB_HALT_SYSTEM;
- if (signal == SIGUSR2) action = RB_POWER_OFF;
- // PID 1 can't call reboot() because it kills the task that calls it,
- // which causes the kernel to panic before the actual reboot happens.
- sync();
- if (getpid()!=1) _exit(127+signal);
- if (!vfork()) reboot(action);
- }
- void oneit_main(void)
- {
- int i, pid, pipes[] = {SIGUSR1, SIGUSR2, SIGTERM, SIGINT};
- // Setup signal handlers for signals of interest
- for (i = 0; i<ARRAY_LEN(pipes); i++) xsignal(pipes[i], oneit_signaled);
- if (FLAG(3)) {
- // Ensure next available filehandles are #3 and #4
- while (xopen_stdio("/", 0) < 3);
- close(3);
- close(4);
- xpipe(pipes);
- fcntl(4, F_SETFD, FD_CLOEXEC);
- }
- while (!toys.signal) {
- // Create a new child process.
- pid = XVFORK();
- if (pid) {
- // pid 1 reaps zombies until it gets its child, then halts system.
- // We ignore the return value of write (what would we do with it?)
- // but save it in a variable we never read to make fortify shut up.
- // (Real problem is if pid2 never reads, write() fills pipe and blocks.)
- while (pid != wait(&i)) if (FLAG(3)) i = write(4, &pid, 4);
- if (FLAG(n)) continue;
- oneit_signaled(FLAG(p) ? SIGUSR2 : SIGTERM);
- } else {
- // Redirect stdio to TT.c, with new session ID, so ctrl-c works.
- setsid();
- for (i=0; i<3; i++) {
- close(i);
- // Remember, O_CLOEXEC is backwards for xopen()
- xopen_stdio(TT.c ? : "/dev/tty0", O_RDWR|O_CLOEXEC);
- }
- // Can't xexec() here, we vforked so we don't want to error_exit().
- toy_exec(toys.optargs);
- execvp(*toys.optargs, toys.optargs);
- perror_msg("%s not in PATH=%s", *toys.optargs, getenv("PATH"));
- break;
- }
- }
- // Give reboot() time to kick in, or avoid rapid spinning if exec failed
- sleep(5);
- _exit(127);
- }
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