/*-
 * Copyright (c) 2005 Pawel Jakub Dawidek <pjd@FreeBSD.org>
 * All rights reserved.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS 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 AUTHORS 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.
 *
 * $FreeBSD: head/lib/libutil/pidfile.c 255007 2013-08-28 21:10:37Z jilles $
 */

#include <sys/param.h>
#include <sys/stat.h>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <time.h>
#include <err.h>
#include <errno.h>
#include <libutil.h>

struct pidfh {
        int     pf_fd;
        char    pf_path[MAXPATHLEN + 1];
        dev_t   pf_dev;
        ino_t   pf_ino;
};

static int _pidfile_remove(struct pidfh *pfh, int freeit);

static int
pidfile_verify(const struct pidfh *pfh)
{
        struct stat sb;

        if (pfh == NULL || pfh->pf_fd == -1)
                return (EDOOFUS);
        /*
         * Check remembered descriptor.
         */
        if (fstat(pfh->pf_fd, &sb) == -1)
                return (errno);
        if (sb.st_dev != pfh->pf_dev || sb.st_ino != pfh->pf_ino)
                return (EDOOFUS);
        return (0);
}

static int
pidfile_read(const char *path, pid_t *pidptr)
{
        char buf[16], *endptr;
        int error, fd, i;

        fd = open(path, O_RDONLY | O_CLOEXEC);
        if (fd == -1)
                return (errno);

        i = read(fd, buf, sizeof(buf) - 1);
        error = errno;  /* Remember errno in case close() wants to change it. */
        close(fd);
        if (i == -1)
                return (error);
        else if (i == 0)
                return (EAGAIN);
        buf[i] = '\0';

        *pidptr = strtol(buf, &endptr, 10);
        if (endptr != &buf[i])
                return (EINVAL);

        return (0);
}

struct pidfh *
pidfile_open(const char *path, mode_t mode, pid_t *pidptr)
{
        struct pidfh *pfh;
        struct stat sb;
        int error, fd, len, count;
        struct timespec rqtp;

        pfh = malloc(sizeof(*pfh));
        if (pfh == NULL)
                return (NULL);

        if (path == NULL)
                len = snprintf(pfh->pf_path, sizeof(pfh->pf_path),
                    "/var/run/%s.pid", getprogname());
        else
                len = snprintf(pfh->pf_path, sizeof(pfh->pf_path),
                    "%s", path);
        if (len >= (int)sizeof(pfh->pf_path)) {
                free(pfh);
                errno = ENAMETOOLONG;
                return (NULL);
        }

        /*
         * Open the PID file and obtain exclusive lock.
         * We truncate PID file here only to remove old PID immediatelly,
         * PID file will be truncated again in pidfile_write(), so
         * pidfile_write() can be called multiple times.
         */
        fd = flopen(pfh->pf_path,
            O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC | O_NONBLOCK, mode);
        if (fd == -1) {
                if (errno == EWOULDBLOCK) {
                        if (pidptr == NULL) {
                                errno = EEXIST;
                        } else {
                                count = 20;
                                rqtp.tv_sec = 0;
                                rqtp.tv_nsec = 5000000;
                                for (;;) {
                                        errno = pidfile_read(pfh->pf_path,
                                            pidptr);
                                        if (errno != EAGAIN || --count == 0)
                                                break;
                                        nanosleep(&rqtp, 0);
                                }
                                if (errno == EAGAIN)
                                        *pidptr = -1;
                                if (errno == 0 || errno == EAGAIN)
                                        errno = EEXIST;
                        }
                }
                free(pfh);
                return (NULL);
        }

        /*
         * Remember file information, so in pidfile_write() we are sure we write
         * to the proper descriptor.
         */
        if (fstat(fd, &sb) == -1) {
                error = errno;
                unlink(pfh->pf_path);
                close(fd);
                free(pfh);
                errno = error;
                return (NULL);
        }

        pfh->pf_fd = fd;
        pfh->pf_dev = sb.st_dev;
        pfh->pf_ino = sb.st_ino;

        return (pfh);
}

int
pidfile_write(struct pidfh *pfh)
{
        char pidstr[16];
        int error, fd;

        /*
         * Check remembered descriptor, so we don't overwrite some other
         * file if pidfile was closed and descriptor reused.
         */
        errno = pidfile_verify(pfh);
        if (errno != 0) {
                /*
                 * Don't close descriptor, because we are not sure if it's ours.
                 */
                return (-1);
        }
        fd = pfh->pf_fd;

        /*
         * Truncate PID file, so multiple calls of pidfile_write() are allowed.
         */
        if (ftruncate(fd, 0) == -1) {
                error = errno;
                _pidfile_remove(pfh, 0);
                errno = error;
                return (-1);
        }

        snprintf(pidstr, sizeof(pidstr), "%u", getpid());
        if (pwrite(fd, pidstr, strlen(pidstr), 0) != (ssize_t)strlen(pidstr)) {
                error = errno;
                _pidfile_remove(pfh, 0);
                errno = error;
                return (-1);
        }

        return (0);
}

int
pidfile_close(struct pidfh *pfh)
{
        int error;

        error = pidfile_verify(pfh);
        if (error != 0) {
                errno = error;
                return (-1);
        }

        if (close(pfh->pf_fd) == -1)
                error = errno;
        free(pfh);
        if (error != 0) {
                errno = error;
                return (-1);
        }
        return (0);
}

static int
_pidfile_remove(struct pidfh *pfh, int freeit)
{
        int error;

        error = pidfile_verify(pfh);
        if (error != 0) {
                errno = error;
                return (-1);
        }

        if (unlink(pfh->pf_path) == -1)
                error = errno;
        if (close(pfh->pf_fd) == -1) {
                if (error == 0)
                        error = errno;
        }
        if (freeit)
                free(pfh);
        else
                pfh->pf_fd = -1;
        if (error != 0) {
                errno = error;
                return (-1);
        }
        return (0);
}

int
pidfile_remove(struct pidfh *pfh)
{

        return (_pidfile_remove(pfh, 1));
}

int
pidfile_fileno(const struct pidfh *pfh)
{

        if (pfh == NULL || pfh->pf_fd == -1) {
                errno = EDOOFUS;
                return (-1);
        }
        return (pfh->pf_fd);
}