source: MondoRescue/branches/3.2/mindi-busybox/libbb/vfork_daemon_rexec.c

/* vi: set sw=4 ts=4: */
/*
 * Rexec program for system have fork() as vfork() with foreground option
 *
 * Copyright (C) Vladimir N. Oleynik <dzo@simtreas.ru>
 * Copyright (C) 2003 Russ Dill <Russ.Dill@asu.edu>
 *
 * daemon() portion taken from uClibc:
 *
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Modified for uClibc by Erik Andersen <andersee@debian.org>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

#include "busybox.h" /* uses applet tables */

/* This does a fork/exec in one call, using vfork().  Returns PID of new child,
 * -1 for failure.  Runs argv[0], searching path if that has no / in it. */
pid_t FAST_FUNC spawn(char **argv)
{
    /* Compiler should not optimize stores here */
    volatile int failed;
    pid_t pid;

    fflush_all();

    /* Be nice to nommu machines. */
    failed = 0;
    pid = vfork();
    if (pid < 0) /* error */
        return pid;
    if (!pid) { /* child */
        /* This macro is ok - it doesn't do NOEXEC/NOFORK tricks */
        BB_EXECVP(argv[0], argv);

        /* We are (maybe) sharing a stack with blocked parent,
         * let parent know we failed and then exit to unblock parent
         * (but don't run atexit() stuff, which would screw up parent.)
         */
        failed = errno;
        /* mount, for example, does not want the message */
        /*bb_perror_msg("can't execute '%s'", argv[0]);*/
        _exit(111);
    }
    /* parent */
    /* Unfortunately, this is not reliable: according to standards
     * vfork() can be equivalent to fork() and we won't see value
     * of 'failed'.
     * Interested party can wait on pid and learn exit code.
     * If 111 - then it (most probably) failed to exec */
    if (failed) {
        safe_waitpid(pid, NULL, 0); /* prevent zombie */
        errno = failed;
        return -1;
    }
    return pid;
}

/* Die with an error message if we can't spawn a child process. */
pid_t FAST_FUNC xspawn(char **argv)
{
    pid_t pid = spawn(argv);
    if (pid < 0)
        bb_simple_perror_msg_and_die(*argv);
    return pid;
}

#if ENABLE_FEATURE_PREFER_APPLETS
struct nofork_save_area {
    jmp_buf die_jmp;
    const char *applet_name;
    uint32_t option_mask32;
    int die_sleep;
    uint8_t xfunc_error_retval;
};
static void save_nofork_data(struct nofork_save_area *save)
{
    memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
    save->applet_name = applet_name;
    save->xfunc_error_retval = xfunc_error_retval;
    save->option_mask32 = option_mask32;
    save->die_sleep = die_sleep;
}
static void restore_nofork_data(struct nofork_save_area *save)
{
    memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
    applet_name = save->applet_name;
    xfunc_error_retval = save->xfunc_error_retval;
    option_mask32 = save->option_mask32;
    die_sleep = save->die_sleep;
}

int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
{
    int rc, argc;
    struct nofork_save_area old;

    save_nofork_data(&old);

    applet_name = APPLET_NAME(applet_no);

    xfunc_error_retval = EXIT_FAILURE;

    /* In case getopt() or getopt32() was already called:
     * reset the libc getopt() function, which keeps internal state.
     *
     * BSD-derived getopt() functions require that optind be set to 1 in
     * order to reset getopt() state.  This used to be generally accepted
     * way of resetting getopt().  However, glibc's getopt()
     * has additional getopt() state beyond optind, and requires that
     * optind be set to zero to reset its state.  So the unfortunate state of
     * affairs is that BSD-derived versions of getopt() misbehave if
     * optind is set to 0 in order to reset getopt(), and glibc's getopt()
     * will core dump if optind is set 1 in order to reset getopt().
     *
     * More modern versions of BSD require that optreset be set to 1 in
     * order to reset getopt().  Sigh.  Standards, anyone?
     */
#ifdef __GLIBC__
    optind = 0;
#else /* BSD style */
    optind = 1;
    /* optreset = 1; */
#endif
    /* optarg = NULL; opterr = 1; optopt = 63; - do we need this too? */
    /* (values above are what they initialized to in glibc and uclibc) */
    /* option_mask32 = 0; - not needed, no applet depends on it being 0 */

    argc = 1;
    while (argv[argc])
        argc++;

    /* Special flag for xfunc_die(). If xfunc will "die"
     * in NOFORK applet, xfunc_die() sees negative
     * die_sleep and longjmp here instead. */
    die_sleep = -1;

    rc = setjmp(die_jmp);
    if (!rc) {
        /* Some callers (xargs)
         * need argv untouched because they free argv[i]! */
        char *tmp_argv[argc+1];
        memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
        /* Finally we can call NOFORK applet's main() */
        rc = applet_main[applet_no](argc, tmp_argv);
    } else { /* xfunc died in NOFORK applet */
        /* in case they meant to return 0... */
        if (rc == -2222)
            rc = 0;
    }

    /* Restoring some globals */
    restore_nofork_data(&old);

    /* Other globals can be simply reset to defaults */
#ifdef __GLIBC__
    optind = 0;
#else /* BSD style */
    optind = 1;
#endif

    return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
}
#endif /* FEATURE_PREFER_APPLETS */

int FAST_FUNC spawn_and_wait(char **argv)
{
    int rc;
#if ENABLE_FEATURE_PREFER_APPLETS
    int a = find_applet_by_name(argv[0]);

    if (a >= 0 && (APPLET_IS_NOFORK(a)
# if BB_MMU
            || APPLET_IS_NOEXEC(a) /* NOEXEC trick needs fork() */
# endif
    )) {
# if BB_MMU
        if (APPLET_IS_NOFORK(a))
# endif
        {
            return run_nofork_applet(a, argv);
        }
# if BB_MMU
        /* MMU only */
        /* a->noexec is true */
        rc = fork();
        if (rc) /* parent or error */
            return wait4pid(rc);
        /* child */
        xfunc_error_retval = EXIT_FAILURE;
        run_applet_no_and_exit(a, argv);
# endif
    }
#endif /* FEATURE_PREFER_APPLETS */
    rc = spawn(argv);
    return wait4pid(rc);
}

#if !BB_MMU
void FAST_FUNC re_exec(char **argv)
{
    /* high-order bit of first char in argv[0] is a hidden
     * "we have (already) re-execed, don't do it again" flag */
    argv[0][0] |= 0x80;
    execv(bb_busybox_exec_path, argv);
    bb_perror_msg_and_die("can't execute '%s'", bb_busybox_exec_path);
}

pid_t FAST_FUNC fork_or_rexec(char **argv)
{
    pid_t pid;
    /* Maybe we are already re-execed and come here again? */
    if (re_execed)
        return 0;
    pid = xvfork();
    if (pid) /* parent */
        return pid;
    /* child - re-exec ourself */
    re_exec(argv);
}
#endif

/* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
 * char **argv "vanishes" */
void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
{
    int fd;

    if (flags & DAEMON_CHDIR_ROOT)
        xchdir("/");

    if (flags & DAEMON_DEVNULL_STDIO) {
        close(0);
        close(1);
        close(2);
    }

    fd = open(bb_dev_null, O_RDWR);
    if (fd < 0) {
        /* NB: we can be called as bb_sanitize_stdio() from init
         * or mdev, and there /dev/null may legitimately not (yet) exist!
         * Do not use xopen above, but obtain _ANY_ open descriptor,
         * even bogus one as below. */
        fd = xopen("/", O_RDONLY); /* don't believe this can fail */
    }

    while ((unsigned)fd < 2)
        fd = dup(fd); /* have 0,1,2 open at least to /dev/null */

    if (!(flags & DAEMON_ONLY_SANITIZE)) {
        if (fork_or_rexec(argv))
            exit(EXIT_SUCCESS); /* parent */
        /* if daemonizing, detach from stdio & ctty */
        setsid();
        dup2(fd, 0);
        dup2(fd, 1);
        dup2(fd, 2);
        if (flags & DAEMON_DOUBLE_FORK) {
            /* On Linux, session leader can acquire ctty
             * unknowingly, by opening a tty.
             * Prevent this: stop being a session leader.
             */
            if (fork_or_rexec(argv))
                exit(EXIT_SUCCESS); /* parent */
        }
    }
    while (fd > 2) {
        close(fd--);
        if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
            return;
        /* else close everything after fd#2 */
    }
}

void FAST_FUNC bb_sanitize_stdio(void)
{
    bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
}