In order to make the device support the asynchronous notification mechanism, the driver involves the following three tasks:
1. Support the F_SETOWN command, which can set filp->f_owner as the corresponding process ID in this control command processing .
However, this work has been done by the kernel, and the device driver does not need to deal with it.
2. Support the processing of the F_SETFL command, whenever the FASYNC flag changes, the fasync() function in the driver will be
executed. The fasync() function
should be implemented in the driver . 3. When the device resource is available, call the kill_fasync() function to stimulate the corresponding signal Application : fcntl(fd, F_SETOWN, getpid()); // Tell the kernel to whom the application will call " fcntl() " function that tells the driver the PID number of the process. The application also reads " flags " through " F_GETFL "
", set the " FASYNC " bit on flags . Oflags = fcntl(fd, F_GETFL); fcntl(fd, F_SETFL, Oflags | FASYNC); // Change the fasync flag, which will eventually call the driver's faync > fasync_helper : initialization / free fasync_struct
The previous method of character-driven:
First, the application program actively queries or reads .
1. Query method: it takes up a lot of resources.
2. Interrupt mechanism: Although there is sleep, read () will wait all the time and never return when no key is pressed . 3.poll mechanism: specify the timeout period. The above are all "applications" actively reading or querying.
今天学习的方式：
二，异步通知：
有按键按下了，驱动程序来提醒（触发）“应用程序”去读键值。用“signal”
进程之间发信号：
kill -9 pid
kill 是信号发送者，
pid 具体进程是信号接收者。
信号值是“9”
“信号”与“中断”差不多。注册中断处理函数时是用“request_irq(中断号，处理函数)”。
信号也是有一个“信号”和“处理函数”。
参数是“信号的值”，和要挂接的“信号处理函数”。
测试信号应用程序：
kill -9 pid： 9 这个信号处理函数就是让这个进程退出来。
1，先注册“信号处理函数”。
2，发送信号。
①，谁来发信号。
②，发给谁。
③，怎么发
三，异步通知功能的驱动函数的应用程序：
目标：按下按键时，驱动程序通知应用程序。（以前是应用程序主动读取按键值）
1，应用程序中要注册“信号处理函数”。因为通知它做什么事情，这要一个函数来做。
2，谁发：是驱动程序发送信号。
3，发给谁：信号发送给应用程序。应用程序要告诉驱动程序它自已的 PID，
4，如何发：驱动程序中调用某个函数（kill_fasync()） 