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异步通知
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驅動程序與應用程序不能直接通信，如果設備已經準備好數據，可以采用異步通知的方式通知應用層來讀取，這樣應用程序就不需要一直查詢設備的狀態。要支持異步通知，需要實現設備驅動程序的fasync接口。當一個打開的文件的FASYNC標志變化時file_operations ->fasync()接口將被調用。file_operations ->fasync函數會調用fasync_helper從相關的進程列表中添加或去除異步通知關聯。
int?fasync_helper(int?fd,?struct?file?*filp,?int?mode,?struct?fasync_struct?**fa);?
當數據到達時 kill_fasync函數將被用來通知相關的進程：
void?kill_fasync(struct?fasync_struct?**fa,?int?sig,?int?band);?
例1.8? 異步通知實例
代碼見光盤\src\1drivermodel\1-8fasync。驅動層代碼如下：
struct?simple_dev?*simple_devices; ?static?unsigned?char?simple_inc=0; ?static?struct?timer_list?simple_timer; ?static?struct?fasync_struct?*fasync_queue=NULL; ?int?simple_open(struct?inode?*inode,?struct?file?*filp) ?{ ?????struct?simple_dev?*dev; ?????dev?=?container_of(inode->i_cdev,?struct?simple_dev,?cdev); ?????filp->private_data?=?dev; ?????simple_timer.function?=?&simple_timer_handler; ?????simple_timer.expires?=?jiffies?+?2*HZ; ?????add_timer?(&simple_timer); ?????printk("add_timer...\n"); ?????return?0; ?} ?//異步通知處理函數 ?static?int?simple_fasync(int?fd,?struct?file?*?filp,?int?mode)? ?{ ?????int?retval; ?????printk("simple_fasync...\n"); ?????retval=fasync_helper(fd,filp,mode,&fasync_queue); ?????if(retval<0) ???????return?retval; ?????return?0; ?} ?int?simple_release(struct?inode?*inode,?struct?file?*filp) ?{ ?????simple_fasync(-1,?filp,?0); ?????return?0; ?} ?struct?file_operations?simple_fops?=?{ ?????.owner?=????THIS_MODULE, ?????.open?=?????simple_open, ?????.release=???simple_release, ?????.fasync=????simple_fasync, ?}; ?
當數據來臨時通知應用層：
static?void?simple_timer_handler(?unsigned?long?data) ?{ ?????printk("simple_timer_handler...\n"); ?????if?(fasync_queue) ?????{ ???????//POLL_IN為可讀，POLL_OUT為可寫 ???????kill_fasync(&fasync_queue,?SIGIO,?POLL_IN); ???????printk("kill_fasync...\n"); ?????} ?????return?; ?} ?
POLL_IN表示設備可讀，POLL_OUT表示設備可寫。應用層參考代碼如下：
int?fd; ?void?fasync_handler(int?num) ?{ ????printf("fasync_handler?entering\n"); ?} ?void?main() ?{ ???int?i=2; ???char?data[256]; ???int?oflags=0; ???int?retval; ???signal(SIGIO,?fasync_handler);//注冊信號處理函數 ???fd=open("/dev/fcn",O_RDWR); ???if(fd==-1) ???{ ??????perror("error?open\n"); ??????exit(-1); ???} ???printf("open?/dev/fcn?successfully\n"); ???//使能了異步的通知到當前進程 ???fcntl(fd,?F_SETOWN,?getpid()); ???oflags=fcntl(fd,?F_GETFL); ???fcntl(fd,?F_SETFL,?oflags?|?FASYNC);//修改文件標志 ???while(1); ???close(fd); ?} ?
運行結果如下：
[root@urbetter?/home]#?insmod?demo.ko ?[root@urbetter?/home]#?mknod?/dev/fcn?c?226?0 ?[root@urbetter?/home]#?./test ?add_timer... ?open?/dev/fcn?successfullysimple_fasync... ??simple_timer_handler... ?kill_fasync... ?fasync_handler?entering ?
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