#include <sys/types.h>
#include <sys/stat.h>
int mkfifo(const char * pathname, mode_t mode);

• 当使用O_NONBLOCK 旗标时, 打开FIFO 文件来读取的操作会立刻返回, 但是若还没有其他进程打开FIFO 文件来读取, 则写入的操作会返回ENXIO 错误代码.
• 没有使用O_NONBLOCK 旗标时, 打开FIFO 来读取的操作会等到其他进程打开FIFO 文件来写入才正常返回. 同样地, 打开FIFO 文件来写入的操作会等到其他进程打开FIFO 文件来读取后才正常返回.

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

#define BUF_SIZ (1024)
#define FIFO_NAME "/tmp/fifo"

int main(void)
{

	char buf[BUF_SIZ];/* buffer */
	int fd; /* file descriptor */	
	unlink(FIFO_NAME);

	if(0 == mkfifo(FIFO_NAME, 0777))
	{
		printf("create fifo successfully.\n");
	}
	else
	{
		printf("create fifo failed.\n");
		return -1;
	}

	
	if(fork() > 0)
	{	
		fd = open(FIFO_NAME, O_WRONLY);
		if(fd > 0)
		{
			printf("Process %d open %s successfully.\n",
				getpid(), FIFO_NAME);
			write(fd, "hello,world", strlen("hello,world"));
		}
	}
	else
	{
		fd = open(FIFO_NAME, O_RDONLY);
		if(fd > 0)
		{
			printf("Process %d open %s successfully.\n",
				getpid(), FIFO_NAME);
			read(fd, buf, BUF_SIZ);
			printf("recv:%s\n", buf);
		}
	}

	close(fd);
}

消息队列

struct msgbuf
  {
    long int mtype;		/* type of received/sent message */
    char mtext[1];		/* text of the message */
  };

结构msgid_ds

struct msqid_ds {
	struct ipc_perm msg_perm;
	struct msg *msg_first;		/* first message on queue,unused  */
	struct msg *msg_last;		/* last message in queue,unused */
	__kernel_time_t msg_stime;	/* last msgsnd time */
	__kernel_time_t msg_rtime;	/* last msgrcv time */
	__kernel_time_t msg_ctime;	/* last change time */
	unsigned long  msg_lcbytes;	/* Reuse junk fields for 32 bit */
	unsigned long  msg_lqbytes;	/* ditto */
	unsigned short msg_cbytes;	/* current number of bytes on queue */
	unsigned short msg_qnum;	/* number of messages in queue */
	unsigned short msg_qbytes;	/* max number of bytes on queue */
	__kernel_ipc_pid_t msg_lspid;	/* pid of last msgsnd */
	__kernel_ipc_pid_t msg_lrpid;	/* last receive pid */
};

/* Obsolete, used only for backwards compatibility and libc5 compiles */
struct ipc_perm
{
	__kernel_key_t	key;/* 用于区分消息队列 */
	__kernel_uid_t	uid;/* 消息队列用户的ID号 */
	__kernel_gid_t	gid;/* 消息队列用户组的ID号 */
	__kernel_uid_t	cuid;/* 消息队列创建者的UID号 */
	__kernel_gid_t	cgid;
	__kernel_mode_t	mode; /* 权限，用户控制读写，0666，可以对消息进行读写操作 */
	unsigned short	seq;
};

#include <sys/types.h>
#include <sys/ipc.h>
key_t ftok(const char * path_name, int proj_id);

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/msg.h>
#include <sys/stat.h>
#include <sys/ipc.h>

#define BUF_SZ (10)
struct msgmbuf
{
	int mtype;
	char mtext[BUF_SZ];
};

int main(void)
{

	int ret = 1;
	int msg_flags , msg_id;
	key_t key;
	struct msqid_ds msg_info;
	struct msgmbuf msg_buf;
	int msg_sflags, msg_rflags;
	char * msg_path = ".";
	
	/* 1.使用ftok创建键值 */
	key = ftok(msg_path, ‘b‘);
	if(key != -1)
		printf("Create Key Successfully.\n");
	else
	{
		printf("Create Key Failed.\n");
		return -1;
	}
	
	/* 2.使用msgget获取消息队列标识符*/
	msg_flags = IPC_CREAT;
	msg_id = msgget(key, msg_flags | 0666);
	if(-1 != msg_id)
	{
		printf("msgget succeed.\n");
	}
	else
	{
		printf("msgget failed.\n");
		return -1;
	}
	
	/* 3.使用msgsnd发送消息 */
	msg_flags = IPC_NOWAIT;
	msg_buf.mtype = 10;
	memcpy(msg_buf.mtext, "hello,linux kernel.", strlen("hello,linux kernel."));
	ret = msgsnd(msg_id, &msg_buf, 10, msg_flags);
	if(ret != -1)
	{
		printf("msgsnd succeed.\n");
	}

	/* 4.使用msgrcv接收消息 */
	msg_flags = IPC_NOWAIT;
	ret = msgrcv(msg_id, &msg_buf, 10, 10, msg_flags);
	if(ret != -1)
	{
		printf("msgrcv succeed.\n");
	}

	/* 5.删除队列 */	
	ret = msgctl(msg_id, IPC_RMID, NULL);
	if(ret != -1)
	{
		printf("msgctl succeed.\n");
	}
}

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