toys/oneit.c

/* vi: set sw=4 ts=4:
 *
 * oneit.c, tiny one-process init replacement.
 *
 * Copyright 2005, 2007 by Rob Landley <rob@landley.net>.
 *
 * Not in SUSv3.

USE_ONEIT(NEWTOY(oneit, "^<1c:p", TOYFLAG_SBIN))

config ONEIT
	bool "oneit"
	default y
	help
	  usage: oneit [-p] [-c /dev/tty0] command [...]

	  A simple init program that runs a single supplied command line with a
	  controlling tty (so CTRL-C can kill it).

	  -p	Power off instead of rebooting when command exits.
	  -c	Which console device to use.

	  The oneit command runs the supplied command line as a child process
	  (because PID 1 has signals blocked), attached to /dev/tty0, in its
	  own session.  Then oneit reaps zombies until the child exits, at
	  which point it reboots (or with -p, powers off) the system.
*/

#include "toys.h"
#include <sys/reboot.h>

DEFINE_GLOBALS(
	char *console;
)

#define TT this.oneit

// 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 /dev/tty0 (/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.


void oneit_main(void)
{
  int i;
  pid_t pid;

  // Create a new child process.
  pid = vfork();
  if (pid) {

    // pid 1 just reaps zombies until it gets its child, then halts the system.
    while (pid!=wait(&i));
    sync();

	// 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.
	if (!vfork()) reboot((toys.optflags&1) ? RB_POWER_OFF : RB_AUTOBOOT);
	sleep(5);
	_exit(1);
  }

  // Redirect stdio to /dev/tty0, with new session ID, so ctrl-c works.
  setsid();
  for (i=0; i<3; i++) {
    close(i);
    xopen(TT.console ? TT.console : "/dev/tty0",O_RDWR);
  }

  // Can't xexec() here, because we vforked so we don't want to error_exit().
  toy_exec(toys.optargs);
  execvp(*toys.optargs, toys.optargs);
  _exit(127);
}