无法打开FIFO

Question

我编写这个程序是为了测试Ubuntu中的FIFO。主程序创建一个子进程来写入某些内容，然后父进程读取并打印它。

/*
   communication with named pipe(or FIFO)
   @author  myqiqiang
   @email   myqiqiang@gmail.com
*/
#include<sys/types.h>
#include<sys/stat.h>
#include<stdio.h>
#include<errno.h>
#include<fcntl.h>
#include<string.h>
#define FIFO_SERVER "/home/myqiqiang/fifoserver" //fifo directioy
#define BUFFERSIZE 80
void main()
{
    pid_t pc;
    int flag,fd;
    char data[BUFFERSIZE+1];
    char* test="a test string";
    if(mkfifo(FIFO_SERVER,O_CREAT|O_EXCL)<0)    //create fifo
    {
        printf("create named pipe failed\n");
        exit(1);
    }
    printf("create named pipe sucessfully\n");
    pc=fork();  //create process
    if(pc==0)
    {
        memset(data,0,strlen(test));
        fd=open(FIFO_SERVER,O_WRONLY,0);    //open the fifo
        if(fd==-1)  //if open failed
        {
            printf("write:cann't open the named pipe\n");
            unlink(FIFO_SERVER);
            exit(1);
        }
        flag=write(fd,test,13);     //write data
        if(flag==-1)    //write failed
        {
            printf("write data error\n");
            unlink(FIFO_SERVER);
            exit(1);
        }
        printf("write data successfully\n");
        close(fd);  //clsoe fifo
        unlink(FIFO_SERVER);    //delete fifo
    }
    else
        if(pc>0)
        {
            memset(data,0,strlen(test));
            fd=open(FIFO_SERVER,O_RDONLY,0);
            if(fd==-1)
            {
                printf("read:cann't open the named pipe\n");
                unlink(FIFO_SERVER);
                exit(1);
            }
            flag=read(fd,data,13);
            if(flag==-1)
            {
                printf("read data error\n");
                unlink(FIFO_SERVER);
                exit(1);
            }
            printf("the data is%s\n",data);
            close(fd);
            unlink(FIFO_SERVER);
        }
        else
        {
            printf("create process error!\n");
            unlink(FIFO_SERVER);
            exit(1);
        }
}

然而，它显示了这一点，每次我执行，我相信先进先出有本板条箱。

myqiqiang@ubuntu:~/code/ch03/experiment$ ./3
create named pipe sucessfully
read:cann't open the named pipe
write:cann't open the named pipe

Answer 1

mkfifo()的第二个参数应该是chmod-type模式(例如0777)，而不是O_标志的组合。

您的进程正在创建一个没有足够权限的管道。

Answer 2

您需要在S_IWUSR、S_IRUSR、S_IRGRP、S_IROTH模式(参考http://pubs.opengroup.org/onlinepubs/009604599/functions/mkfifo.html )中使用mkfifo。

if(mkfifo(FIFO_SERVER, S_IWUSR | S_IRUSR | S_IRGRP | S_IROTH)<0)

Answer 3

当您执行mkfifo并以普通用户(不是root用户)的身份运行时，您的权限是：

P-wx

因此，您需要读取权限，最简单的方法是将其添加到mkfifo标志：

if(mkfifo(FIFO_SERVER，O_CREAT|O_EXCL|S_IRWXU)<0)

它将创建您可以从以下位置读取的文件：

prwx