linux 下串口独占方式打开

参考文章: http://blog.csdn.net/rl529014/article/details/51336161

　　　　 http://blog.csdn.net/lin_fs/article/details/7804494

 　　　　http://blog.csdn.net/querdaizhi/article/details/7478169

  　以flock函数打开设备文件打开，是独占整个文件

　　int fd;
    char com_name[20]={0};
    sprintf(com_name,"/dev/ttyS100%d",com_port);
    // sprintf(com_name,"/dev/ttyS%d",1);
    // printf("before first open
");
    fd = open(com_name, O_RDWR|O_NOCTTY|O_NDELAY);
    // fd = open(com_name, O_RDWR|O_EXCL,0444);
    if (fd < 0)
    {
            perror("open serial port");
            return(-1);
    }

        if(flock(fd,LOCK_EX|LOCK_NB)==0)
        {
           printf("the file was not locked.
");
        }
    else
        {
          printf("the file was locked.
");
          close(fd);
          return -1;
       }

      
        
    if (fcntl(fd, F_SETFL, 0) < 0)
    {
        perror("fcntl F_SETFL
");
    }
    
    if (isatty(STDIN_FILENO) == 0)
    {
        perror("standard input is not a terminal device");
    }
    
    return fd;

 以fcntl方式打开设备文件:

　　

int fd;

    char com_name[20]={0};
    sprintf(com_name,"/dev/ttyS100%d",com_port);
    // sprintf(com_name,"/dev/ttyS%d",1);
    // printf("before first open
");
    fd = open(com_name, O_RDWR|O_NOCTTY|O_NDELAY);
    // fd = open(com_name, O_RDWR|O_EXCL,0444);
    if (fd < 0)
    {
            perror("open serial port");
            return(-1);
    }
    // printf("first open
");


    struct flock lock;
    lock.l_type=F_WRLCK;
    lock.l_pid=getpid();
    lock.l_whence=SEEK_SET;
    lock.l_start=0;
    lock.l_len=0;


    fcntl(fd,F_GETLK,&lock);
    

    if(lock.l_type != F_UNLCK){
         // printf("%d
", lock.l_type);
         return -1;
    }



    lock.l_type=F_WRLCK;
    lock.l_pid=getpid();
    lock.l_whence=SEEK_SET;
    lock.l_start=0;
    lock.l_len=0;

    if(fcntl(fd, F_SETLKW,&lock) < 0){
         perror("fcntl F_SETLKW
");
    }


    
    if (isatty(STDIN_FILENO) == 0)
    {
        perror("standard input is not a terminal device");
    }
    
    return fd;

　　

 F_SETLKW 与  F_SETFL的区别是如果有其他锁阻止该锁被建立，则调用进程进入睡眠状态，等待该锁释放。一旦这个调用开始了等待，就只有在能够进行加锁或者收到信号时才会返回。

而且F_SETFL设置方式为fcntl(STDOUT_FILENO,F_SETFL,flags)，而非fcntl(fd, F_SETLKW,&lock)，无法建立锁机制。    F_SETFL 与 F_SETLKW 使用差别比较大