svr_common.c

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/*
 * Some common functions to build a daemon server program.
 *
 * Copyright (c) 2004, by:      Jian Shen
 *    All rights reserved.      Peking University, China
 *                             <[e-mail]>
 *
 * This file may be used subject to the terms and conditions of the
 * GNU Library General Public License Version 2, or any later version
 * at your option, as published by the Free Software Foundation.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 *
 */

#include "svr_common.h"

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>


static int lock_reg(int fd, int cmd, int type, off_t offset, int whence, off_t len)
{
	struct flock lock;

	lock.l_type = type;
	lock.l_start = offset;
	lock.l_whence = whence;
	lock.l_len = len;

	return (fcntl(fd, cmd, &lock));
}

#define write_lock(fd, offset, whence, len) lock_reg(fd, F_SETLK, F_WRLCK, offset, whence, len)

void check_single_on(const char* PIDFILE, const char* svr_name)
{
	int fd, val;
	char buf[10];

	if((fd = open(PIDFILE, O_WRONLY | O_CREAT, 0644)) <0 ) {
		perror("open in check_single_on()");
		exit(1);
	}

	/* try and set a write lock on the entire file */
	if(write_lock(fd, 0, SEEK_SET, 0) <0 ) {
		if(errno == EACCES || errno == EAGAIN) {
			printf("%s daemon is already running.\n", svr_name);
			exit(0);			/* gracefully exit, daemon is already running */
		}else {
			perror("write_lock");
			close(fd);
			exit(1);
		}
	}

	/* truncate to zero length, now that we have the lock */
	if(ftruncate(fd, 0) <0) {
		perror("ftruncate");
		close(fd);		
		exit(1);
	}

	/* write our process id */
	sprintf(buf, "%d\n", getpid());
	if(write(fd, buf, strlen(buf)) != strlen(buf)) {
		perror("write in check_single_on()");
		close(fd);		
		exit(1);
	}

	/* set close-on-exec flag for descriptor */
	if((val = fcntl(fd, F_GETFD, 0) <0 )) {
		perror("fcntl");
		close(fd);
		exit(1);
	}
	val |= FD_CLOEXEC;
	if(fcntl(fd, F_SETFD, val) <0 ) {
		perror("fcntl again");
		close(fd);
		exit(1);
	}

	/* leave file open until we terminate: lock will be held */

}

int check_proc_running(const char* PIDFILE, const char* svr_name)
{
	int fd, rv;
	char buf[10];

	if((fd = open(PIDFILE, O_RDWR, 0644)) <0 ) {
		printf("%s is not running now.\n", svr_name);
		exit(1);
	}

	/* try and set a write lock on the entire file */
	if(write_lock(fd, 0, SEEK_SET, 0) <0 ) {
		if(errno == EACCES || errno == EAGAIN) {
			/* migsvr server is running, we should return it's pid */

			bzero(buf, 10);
			rv = read(fd, buf, 10);
			buf[rv] = '\0';

			close(fd);
			return atoi(buf);
		}else {
			perror("write_lock");
			close(fd);
			return -1;
		}
	}

	close(fd);

	printf("%s is not running now.\n", svr_name);

	return -1;

}

/* to be a daemon process */
int daemon_init()
{
	pid_t pid;

	if((pid = fork()) <0)
		return -1;
	else if(pid !=0 )
		exit(0);				/* parent goes bye-bye */

	/* child continues */

//	setsid();					/* become session leader */

	chdir("/");					/* change working directory */

	umask(0);					/* clear our file mode creation mask */

	return 0;
}

void daemon_notty()
{
	setsid();					/* become session leader */
}