Why do many device drivers have an IoCompleteRequest(irp,IO_NO_INCREMENT); at the end of the dispatch routines? I read the corresponding Microsoft docs for the IoCompleteRequest function, but I didn't understand very well those concepts.

CodePudding user response：

First, you need to understand the lifecycle of an IRP. How the IRP is created (IoAllocateIrp), delivered (IoCallDriver), and released (IoFreeIrp) after work is done. Second, if necessary, when post-processing is required at the end of the operation, the processing of the I/O completion routine is also handled in the driver hierarchical manner. IoCompleteRequest does the job of ensuring these two things.

1. Application performs an I/O request.
2. I/O Manager (create IRP, pass to driver)
3. Driver (IRP complete after processing the job (IoCompleteRequest))
4. I/O Manager (Release IRP, transfer result to upper application)
5. The application receives the I/O result.