alix-usv/daemon/pidfile.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>

#include "logging.h"

int pidfile_create(const char *filename)
{
	int fd = open(filename, O_CREAT | O_EXCL | O_RDWR, 0644);
	if (fd < 0)
		return -1;

	char buf[8];
	int len = snprintf(buf, sizeof(buf), "%d", getpid());
	write(fd, buf, len);

	close(fd);
	return 0;
}

int pidfile_remove(const char *filename)
{
	return unlink(filename);
}

pid_t pidfile_check(const char *filename, int remove_stale)
{
	int fd = open(filename, O_RDWR);
	if (fd < 0) {
		if (errno == ENOENT) {
			errno = 0;
			return 0;
		}
		return -1;
	}

	char buf[9];
	int len = read(fd, buf, sizeof(buf) -1);
	buf[len] = '\0';

	close(fd);

	char *tmp;
	pid_t pid = strtol(buf, &tmp, 10);
	if (len == 0 || tmp == buf)
		pid = -1;

	/* just return the pid */
	if (!remove_stale)
		return pid;

	/* invalid pid, remove stale file */
	if (pid == -1) {
		pidfile_remove(filename);
		return 0;
	}

	/* check if pid is still running */
	if (kill(pid, 0) == 0 || errno != ESRCH) {
		errno = 0;
		return pid;
	}

	errno = 0;
	pidfile_remove(filename);
	return 0;
}