/*
 * Copyright (c) 2005 The DragonFly Project.  All rights reserved.
 * 
 * This code is derived from software contributed to The DragonFly Project
 * by Joerg Sonnenberger <joerg@bec.de>.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * $DragonFly: src/usr.bin/shlock/shlock.c,v 1.1 2005/07/23 19:47:15 joerg Exp $
 */

#include <sys/types.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <limits.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define BUFSIZE         16

static int      create_lock(const char *, pid_t, int, int);
static int      check_lock(const char *, int, int);
static void     usage(void);

int
main(int argc, char **argv)
{
        int ch, debug = 0, uucpstyle = 0;
        const char *file = NULL;
        char *endptr;
        pid_t pid = -1;
        long tmp_pid;

        while ((ch = getopt(argc, argv, "df:p:u")) != -1) {
                switch (ch) {
                case 'd':
                        debug = 1;
                        break;
                case 'f':
                        file = optarg;
                        break;
                case 'p':
                        errno = 0;
                        tmp_pid = strtol(optarg, &endptr, 10);
                        if (*endptr != '\0' || errno ||
                            tmp_pid < 1 || (pid = tmp_pid) != tmp_pid)
                                errx(1, "invalid pid specified");
                        break;
                case 'u':
                        uucpstyle = 1;
                        break;
                default:
                        usage();
                }
        }
        argc -= optind;
        argv += optind;

        if (argc != 0)
                usage();

        if (file == NULL)
                usage();

        if (pid != -1)
                return(create_lock(file, pid, uucpstyle, debug));
        else
                return(check_lock(file, uucpstyle, debug));
}

static int
create_lock(const char *file, pid_t pid, int uucpstyle, int debug)
{
        char buf[BUFSIZE], tmpf[PATH_MAX];
        char *tmpbuf;
        char *dir;
        int fd, ret;

        ret = snprintf(buf, sizeof(buf), "%ld\n", (long)pid);
        if (ret >= (int)sizeof(buf) || ret == -1)
                err(1, "snprintf() failed"); /* Must not happen. */

        tmpbuf = strdup(file);
        if ((dir = dirname(tmpbuf)) == NULL)
                err(1, "dirname() failed");

        ret = snprintf(tmpf, sizeof(tmpf), "%s/shlock%ld", dir, (long)getpid());
        if (ret >= (int)sizeof(tmpf) || ret == -1)
                err(1, "snprintf failed");
        free(tmpbuf);

        if (debug) {
                printf("%s: trying lock file %s for process %ld\n",
                       getprogname(), file, (long)pid);
        }

        while ((fd = open(tmpf, O_RDWR | O_CREAT | O_EXCL, 0644)) == -1){
                if (errno != EEXIST)
                        err(1, "could not create tempory lock file");
                if (debug)
                        warnx("temporary lock file %s existed already", tmpf);
                if (unlink(tmpf) && errno != ENOENT) {
                        err(1, "could not remove old temporary lock file %s",
                            tmpf);
                }
                /* Try again. */
        }

        if ((uucpstyle && write(fd, &pid, sizeof(pid)) != sizeof(pid)) ||
            (!uucpstyle && write(fd, buf, strlen(buf)) != (int)strlen(buf))) {
                warn("could not write PID to temporary lock file");
                close(fd);

                if (unlink(tmpf))
                        err(1, "could not remove temporary lock file %s", tmpf);

                return(1);              
        }

        close(fd);

        while (link(tmpf, file)) {
                if (errno != EEXIST) {
                        if (unlink(tmpf)) {
                                err(1,
                                    "could not remove temporary lock file %s",
                                    tmpf);
                        }
                        err(1, "could not create lock file");
                }
                if (check_lock(file, uucpstyle, debug) == 0) {
                        if (unlink(tmpf)) {
                                err(1,
                                    "could not remove temporary lock file %s",
                                    tmpf);
                        }
                        return(1); /* Lock file is valid. */
                }
                if (unlink(file) == 0) {
                        printf("%s: stale lock file removed\n", getprogname());
                        continue;
                }
                if (unlink(tmpf)) {
                        err(1, "could not remove temporary lock file %s",
                            tmpf);
                }
                err(1, "could not remove stale lock file");
        }

        if (debug)
                printf("%s: lock successfully obtained\n", getprogname());

        if (unlink(tmpf))
                warn("could not remove temporary lock file %s", tmpf);

        return(0);
}

static int
check_lock(const char *file, int uucpstyle, int debug)
{
        char buf[BUFSIZE];
        int fd;
        ssize_t len;
        pid_t pid;

        if ((fd = open(file, O_RDONLY)) == -1) {
                switch (errno) {
                case ENOENT:
                        return(1); /* File doesn't exist. */
                default:
                        /*
                         * Something went wrong, bail out as
                         * if the lock existed.
                         */
                        err(1, "could not open lock file");
                }
        }

        len = read(fd, buf, uucpstyle ? sizeof(pid_t) : sizeof(buf));
        close(fd);

        if (len < 0) {
                if (debug)
                        warn("could not read lock file");
                return(1);
        }
        if (len == 0) {
                if (debug)
                        warnx("found empty lock file");
                return(1);
        }
        if (uucpstyle) {
                if (len != sizeof(pid_t)) {
                        if (debug)
                                warnx("invalid lock file format");
                        return(1);
                }
                memcpy(&pid, buf, sizeof(pid_t));
        } else {
                char *endptr;
                long tmp_pid;

                if (len == BUFSIZE) {
                        if (debug)
                                warnx("invalid lock file format");
                        return(1);
                }

                buf[BUFSIZE - 1] = '\0';
                errno = 0;
                tmp_pid = strtol(buf, &endptr, 10);
                if ((*endptr != '\0' && *endptr != '\n') || errno ||
                    tmp_pid < 1 || (pid = tmp_pid) != tmp_pid) {
                        if (debug)
                                warnx("invalid lock file format");
                        return(1);
                }
        }

        if (kill(pid, 0) == 0)
                return(0); /* Process is alive. */

        switch (errno) {
        case ESRCH:
                return(1); /* Process is dead. */
        case EPERM:
                return(0); /* Process is alive. */
        default:
                return(0); /* Something else, assume alive. */
        }
}

static void
usage(void)
{
        fprintf(stderr, "%s [-u] [-d] [-p pid] -f file\n", getprogname());
        exit(1);
}