libpidutil/pidutil.c

/*-
 * Copyright (c) 2016, Babak Farrokhi
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 *
 * * 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 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 HOLDER 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.
*/

#include "pidutil.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);

#ifdef __linux__
#define PROGNAME program_invocation_short_name
#else
#define PROGNAME getprogname()
#endif					/* __linux__ */

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

	if (pfh == NULL || pfh->pf_fd == -1)
		return (EINVAL);
	/*
	 * 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 (EINVAL);
	return (0);
}

int
flopen(const char *path, int flags,...)
{
	int fd, operation, serrno, trunc;
	struct stat sb, fsb;
	int mode;

#ifdef O_EXLOCK
	flags &= ~O_EXLOCK;
#endif

	mode = 0;
	if (flags & O_CREAT) {
		va_list ap;

		va_start(ap, flags);
		mode = (int)va_arg(ap, int);
		va_end(ap);
	}
	operation = LOCK_EX;
	if (flags & O_NONBLOCK)
		operation |= LOCK_NB;

	trunc = (flags & O_TRUNC);
	flags &= ~O_TRUNC;

	for (;;) {
		if ((fd = open(path, flags, mode)) == -1)
			/* non-existent or no access */
			return (-1);
		if (flock(fd, operation) == -1) {
			/* unsupported or interrupted */
			serrno = errno;
			(void)close(fd);
			errno = serrno;
			return (-1);
		}
		if (stat(path, &sb) == -1) {
			/* disappeared from under our feet */
			(void)close(fd);
			continue;
		}
		if (fstat(fd, &fsb) == -1) {
			/* can't happen [tm] */
			serrno = errno;
			(void)close(fd);
			errno = serrno;
			return (-1);
		}
		if (sb.st_dev != fsb.st_dev ||
		    sb.st_ino != fsb.st_ino) {
			/* changed under our feet */
			(void)close(fd);
			continue;
		}
		if (trunc && ftruncate(fd, 0) != 0) {
			/* can't happen [tm] */
			serrno = errno;
			(void)close(fd);
			errno = serrno;
			return (-1);
		}
		return (fd);
	}
}

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 timespec rqtp;
	struct stat sb;
	size_t len;
	int fd, error, count;

	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", PROGNAME);
	else
		len = snprintf(pfh->pf_path, sizeof(pfh->pf_path), "%s", path);

	if (len >= sizeof(pfh->pf_path)) {
		free(pfh);
		errno = ENAMETOOLONG;
		return (NULL);
	}
	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);
	}
	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);
}

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_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);
}

int
pidfile_fileno(const struct pidfh *pfh)
{

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