source: MondoRescue/branches/2.2.5/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 tarball for details.
 */

#include <paths.h>
#include "busybox.h" /* for struct bb_applet */

/* 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 spawn(char **argv)
{
    /* Compiler should not optimize stores here */
    volatile int failed;
    pid_t pid;

// Ain't it a good place to fflush(NULL)?

    /* 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;
        _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) {
        errno = failed;
        return -1;
    }
    return pid;
}

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

// Wait for the specified child PID to exit, returning child's error return.
int wait4pid(int pid)
{
    int status;

    if (pid <= 0) {
        /*errno = ECHILD; -- wrong. */
        /* we expect errno to be already set from failed [v]fork/exec */
        return -1;
    }
    if (waitpid(pid, &status, 0) == -1)
        return -1;
    if (WIFEXITED(status))
        return WEXITSTATUS(status);
    if (WIFSIGNALED(status))
        return WTERMSIG(status) + 1000;
    return 0;
}

int wait_nohang(int *wstat)
{
    return waitpid(-1, wstat, WNOHANG);
}

int wait_pid(int *wstat, int pid)
{
    int r;

    do
        r = waitpid(pid, wstat, 0);
    while ((r == -1) && (errno == EINTR));
    return r;
}

#if ENABLE_FEATURE_PREFER_APPLETS
void save_nofork_data(struct nofork_save_area *save)
{
    memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
    save->current_applet = current_applet;
    save->xfunc_error_retval = xfunc_error_retval;
    save->option_mask32 = option_mask32;
    save->die_sleep = die_sleep;
    save->saved = 1;
}

void restore_nofork_data(struct nofork_save_area *save)
{
    memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
    current_applet = save->current_applet;
    xfunc_error_retval = save->xfunc_error_retval;
    option_mask32 = save->option_mask32;
    die_sleep = save->die_sleep;

    applet_name = current_applet->name;
}

int run_nofork_applet_prime(struct nofork_save_area *old, const struct bb_applet *a, char **argv)
{
    int rc, argc;

    current_applet = a;
    applet_name = a->name;
    xfunc_error_retval = EXIT_FAILURE;
    /*option_mask32 = 0; - not needed */
    /* 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;

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

    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 = a->main(argc, tmp_argv);
    } else { /* xfunc died in NOFORK applet */
        /* in case they meant to return 0... */
        if (rc == -2222)
            rc = 0;
    }

    /* Restoring globals */
    restore_nofork_data(old);
    return rc;
}

int run_nofork_applet(const struct bb_applet *a, char **argv)
{
    struct nofork_save_area old;

    /* Saving globals */
    save_nofork_data(&old);
    return run_nofork_applet_prime(&old, a, argv);
}
#endif /* FEATURE_PREFER_APPLETS */

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

    if (a && (a->nofork
#if BB_MMU
         || a->noexec /* NOEXEC trick needs fork() */
#endif
    )) {
#if BB_MMU
        if (a->nofork)
#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;
        current_applet = a;
        run_current_applet_and_exit(argv);
#endif
    }
#endif /* FEATURE_PREFER_APPLETS */
    rc = spawn(argv);
    return wait4pid(rc);
}

#if !BB_MMU
void 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("exec %s", bb_busybox_exec_path);
}

void forkexit_or_rexec(char **argv)
{
    pid_t pid;
    /* Maybe we are already re-execed and come here again? */
    if (re_execed)
        return;

    pid = vfork();
    if (pid < 0) /* wtf? */
        bb_perror_msg_and_die("vfork");
    if (pid) /* parent */
        exit(0);
    /* child - re-exec ourself */
    re_exec(argv);
}
#else
/* Dance around (void)...*/
#undef forkexit_or_rexec
void forkexit_or_rexec(void)
{
    pid_t pid;
    pid = fork();
    if (pid < 0) /* wtf? */
        bb_perror_msg_and_die("fork");
    if (pid) /* parent */
        exit(0);
    /* child */
}
#define forkexit_or_rexec(argv) forkexit_or_rexec()
#endif

/* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
 * char **argv "vanishes" */
void 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 = xopen(bb_dev_null, O_RDWR);

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

    if (!(flags & DAEMON_ONLY_SANITIZE)) {
        forkexit_or_rexec(argv);
        /* if daemonizing, make sure we detach from stdio & ctty */
        setsid();
        dup2(fd, 0);
        dup2(fd, 1);
        dup2(fd, 2);
    }
    while (fd > 2) {
        close(fd--);
        if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
            return;
        /* else close everything after fd#2 */
    }
}

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