linux 下串口獨占方式打開

參考文章: 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函數打開設備文件打開，是獨占整個文件

　　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\n");
    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.\n");
        }
    else
        {
          printf("the file was locked.\n");
          close(fd);
          return -1;
       }

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

 

 以fcntl方式打開設備文件:

　　

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\n");
    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\n");


    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\n", 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\n");
    }


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

　　

 F_SETLKW 與  F_SETFL的區別是如果有其他鎖阻止該鎖被建立，則調用進程進入睡眠狀態，等待該鎖釋放。一旦這個調用開始了等待，就只有在能夠進行加鎖或者收到信號時才會返回。

而且F_SETFL設置方式為fcntl(STDOUT_FILENO,F_SETFL,flags)，而非fcntl(fd, F_SETLKW,&lock)，無法建立鎖機制。    F_SETFL 與 F_SETLKW 使用差別比較大