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

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

    if (fcntl(fd, F_SETFL, ) < )
    {
        perror("fcntl F_SETFL\n");
    }

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

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

    fcntl(fd,F_GETLK,&lock);

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

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

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

    if (isatty(STDIN_FILENO) == )
    {
        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