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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};
char *ss = toybuf+5;
// Setup signal handlers for signals of interest
for (i = 0; i<ARRAY_LEN(pipes); i++) xsignal(pipes[i], oneit_signaled);
// Autodetect console from sysfs if no -c
memcpy(toybuf, "/dev/", 5);
if (!TT.c && (TT.c = readfile("/sys/class/tty/console/active", ss, 4096))) {
// Remove null terminator, take last entry
for (;;) {
if (!(ss = strchr(TT.c, '\n'))) break;
if (!ss[1]) *ss = 0;
else TT.c = ++ss;
}
// Ensure /dev prefix
strstart(&TT.c, "/dev/");
memmove(toybuf+5, TT.c, strlen(TT.c));
TT.c = toybuf;
}
// Redirect stdin/out/err. Remember, O_CLOEXEC is backwards for xopen()
close(0);
xopen_stdio(TT.c ? : "/dev/tty0", O_RDWR|O_CLOEXEC);
close(1);
dup(0);
close(2);
dup(0);
if (FLAG(3)) {
// Ensure next available filehandles are #3 and #4
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 {
// new session ID in child, so ctrl-c works.
setsid();
// 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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