Asynchronous notifications and asynchronous I/O for Linux kernel development (IV)

"John, come on yesterday, do you know? In asynchronous Io, what can be used as AIO notifications ?" I looked at her with longing eyes.

"Ah? Well, I know what you said, I can remember it. It's good to let me invent and create it, but I won't. "John wronged.

"Stupid, I spent so much time talking about signals and other things in front of me. I think of signals as asynchronous notification signals and I want to tell you, I can think of it all the time, but you .. i'm disappointed. "I sighed," Forget it, and you are not the blame. Let's start learning."

FirstCode: Use signals as AIO asynchronous Io notification mechanisms

 Void Setup_io (..){ Int FD; Struct Sigaction sig_act; Struct Aiocb my_aiocb ;... // Set the signal processing function Sigemptyset (& sig_act.sa_mask); sig_act.sa_flags = sa_siginfo; sig_act.sa_sigaction = aio_completion_handler; // Set the AIO request Bzero ((Char *) & My_aiocb, Sizeof ( Struct Aiocb); my_aiocb.aio_flags = FD; my_aiocb.aio_buf = Malloc (Buf_size + 1); my_aiocb.aio_nbytes = buf_size; my_aiocb.offset = next_offset; // Connect AIO requests and signal processing functions My_aiocb.aio_sigevent.sigev_policy = sigev_signval; my_aiocb.aio_sigevent.sigev_signo = sigio; Signature = & my_aiocb; // Bind the signal and processing function Ret = sigaction (sigion, & sig_act, null);... ret = aio_read (& my_aiocb );} // Signal Processing Function  Void Aio_completion_handler ( Int Signo, siginfo_t * info, Void * Context ){ Struct Aiocb * req; // Determine the signal we need      If (Info-> si_signo = sigio) {Req = ( Struct Aiocb *) Info-> si_value.sival_ptr; // Obtain aiocb;       // Whether the requested operation is complete       If (Aio_error (req) = 0) {ret = aio_return (req );}} Return ;}

We can see from the above that the application using AIOProgramYou also need to define a signal processing function to call this processing program when a specified signal is generated.

"Does it mean you can only use signals in this way? I remember that you have told me a lot about none of the previous knowledge points. This song is no exception," said Xiao Wang.

"Well, it's really smart. I like smart girls." I also want to say no when I hear that John knows how to get started.

Code again: the most AIO notification using the callback function

 Void Setup_io (..){... // Same as above      // Connect the AIO request and the thread callback function My_aiocb.aio_sigevent.sigev_policy = sigev_thread; my_aiocb.aio_sigevent.policy_function = aio_completion_handler; // Set the callback function My_aiocb.aio_sigevent.policy_attributes = NULL; my_aiocb.aio_sigevent.sigev_value.sival_ptr = & my_aiocb;... ret = aio_read (& my_aiocb );} // Signal Processing Function  Void Aio_completion_handler ( Int Signo, siginfo_t * info, Void * Context ){ Struct Aiocb * req; Req = ( Struct Aiocb *) sigval. sival_ptr; // Obtain aiocb;       // Whether the requested operation is complete      If (Aio_error (req) = 0) {ret = aio_return (req );} Return ;}

After the above program creates an aiocb request, it uses sigev_thread to request a thread callback function as the notification method. In the callback function. Pass (StructAiocb *) Info-> si_value.sival_ptr can obtain the corresponding aiocb pointer, and use the AIO function to verify whether the request has been completed.

"However, Mr. Wang, I'm sorry. I couldn't expect it to stop. I just talked about the relevant applications. In the next section, we will start to talk about AIO and driver devices, and return to the driver topic ".