Книга: Writing Windows WDM Device Drivers
Dispatch Routine IRPs
Dispatch Routine IRPs
Table 7.1 lists the most common Win32 functions that are used to access devices. A CreateFile call to your device ends up as a Create IRP, an I/O Request Packet with a major function code of IRP_MJ_CREATE. The driver routine to handle this IRP can have any name. However, I use a generic name for the Create IRP handler of Create. In your driver, you would usually put a short name or acronym in front of this base name. The Wdm1 device driver's Create IRP handler is called Wdm1Create.
Table 7.1 is not an exhaustive list of Win32 functions and their matching IRPs. For example, ReadFile has several variants, such as ReadFileEx, but they all end up as IRP_MJ_READ requests. IRPs can also be issued by Windows on behalf of the user program. For example, if an application terminates unexpectedly, the operating system will try to tidy any open files by issuing an IRP_MJ_CLOSE IRP to each file.
Table 7.1 Common dispatch routines
| Win32 Function | IRP Major Code | Base Driver routine name |
|---|---|---|
CreateFile |
IRP_MJ_CREATE |
Create |
CloseHandle |
IRP_MJ_CLOSE |
Close |
ReadFile |
IRP_MJ_READ |
Read |
WriteFile |
IRP_MJ_WRITE |
Write |
DeviceIoControl |
IRP_MJ_DEVICE_CONTROL |
DeviceControl |
A driver need not handle all these IRPs, though handling Create and Close IRPs is an obvious minimum. Its DriverEntry routine sets up the entry points that are valid. If an entry point is not set, then the I/O Manager fails the Win32 request and GetLastError returns 1.
The following line in DriverEntry sets the Wdm1Read routine as the handler for Read IRPs.
DriverObject->MajorFunction[IRP_MJ_READ] = Wdm1Read;
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