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