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概述

irp请求会从io管理器中传递到设备栈中依次向下发送，当到达底层真实设备处理完成后，会依次返回，这时如果在设备栈中有我们自己注册的设备，就可以起到一个过滤的功能。键盘过滤驱动就是如此，通过附加到原本存在的设备KeyboardClass0中，这时当发生按键时irp也会返回到我们的设备中，进而实现起响应。

注意

在整个键盘响应过程中，有一个名为csrss.exe的程序，其会不断的向KeyboardClass0发送读取类型的irp请求，如果我们直接通过断开设备附加再卸载我们的驱动时，就会蓝屏。原因是csrss.exe最终发送的读irp请求已经通过我们最先注册的过滤驱动向下传递了，这时我们卸载了我们自己的驱动，底层返回的irp找不到回调，这时就会蓝屏，所以代码中应该对irp的数量做一个统计，保证其正确处理。

源码

#include<ntifs.h>typedef struct
{PDEVICE_OBJECT LowerKbdDevice;
}DEVICE_EXTENTION,*PDEVICE_EXTENTION;PDEVICE_OBJECT myKbdDevice = NULL;typedef struct _KEYBOARD_INPUT_DATA {USHORT UnitId;USHORT MakeCode;USHORT Flags;USHORT Reserved;ULONG  ExtraInformation;
} KEYBOARD_INPUT_DATA, * PKEYBOARD_INPUT_DATA;
//IRP等待处理的数量
ULONG pendingkey = 0;VOID DriverUnload(PDRIVER_OBJECT DriverObject)
{LARGE_INTEGER interval = { 0 };PDEVICE_OBJECT DeviceObject = DriverObject->DeviceObject;IoDetachDevice(((PDEVICE_EXTENTION)DeviceObject->DeviceExtension)->LowerKbdDevice);interval.QuadPart = -10 * 1000 * 1000;//判断是否还有未处理的IRPwhile (pendingkey){KeDelayExecutionThread(KernelMode, FALSE, &interval);}IoDeleteDevice(myKbdDevice);KdPrint(("驱动卸载结束！\n"));
}NTSTATUS ReadComplete(PDEVICE_OBJECT DeviceObject, PIRP irp, PVOID Context)
{PKEYBOARD_INPUT_DATA KeyBuffer = irp->AssociatedIrp.SystemBuffer;char* key[4] = { "KeyDown","KeyUp","E0","E1" };int structnum = irp->IoStatus.Information / sizeof(KEYBOARD_INPUT_DATA);if (irp->IoStatus.Status == STATUS_SUCCESS){for (int i = 0; i < structnum; i++){KdPrint(("MakeCode = %x,Flags = %s\n", KeyBuffer->MakeCode, key[KeyBuffer->Flags]));}}//处理完成需要将标志位设置，以声明以完成此irp的返回处理if (irp->PendingReturned){IoMarkIrpPending(irp);}pendingkey--;return irp->IoStatus.Status;
}NTSTATUS DispatchPass(PDEVICE_OBJECT pDeviceObject,PIRP irp)
{IoCopyCurrentIrpStackLocationToNext(irp);return IoCallDriver(((PDEVICE_EXTENTION)pDeviceObject->DeviceExtension)->LowerKbdDevice, irp);
}NTSTATUS DispatchRead(PDEVICE_OBJECT pDeviceObject, PIRP irp)
{IoCopyCurrentIrpStackLocationToNext(irp);IoSetCompletionRoutine(irp,ReadComplete,NULL,TRUE,TRUE,TRUE,TRUE);pendingkey++;return IoCallDriver(((PDEVICE_EXTENTION)pDeviceObject->DeviceExtension)->LowerKbdDevice, irp);
}NTSTATUS MyAttachDevice(PDRIVER_OBJECT pDriverObject)
{UNICODE_STRING kbdName = RTL_CONSTANT_STRING(L"\\Device\\KeyboardClass0");NTSTATUS status = IoCreateDevice(pDriverObject, sizeof(DEVICE_EXTENTION), NULL, 0, FILE_DEVICE_KEYBOARD, NULL, &myKbdDevice);if (!NT_SUCCESS(status)){return status;}myKbdDevice->Flags |= DO_BUFFERED_IO;myKbdDevice->Flags &= ~DO_DEVICE_INITIALIZING;RtlZeroMemory(myKbdDevice->DeviceExtension,sizeof(DEVICE_EXTENTION));status = IoAttachDevice(myKbdDevice, &kbdName, &((PDEVICE_EXTENTION)myKbdDevice->DeviceExtension)->LowerKbdDevice);if (!NT_SUCCESS(status)){IoDeleteDevice(myKbdDevice);return status;}return STATUS_SUCCESS;
}NTSTATUS DriverEntry(PDRIVER_OBJECT pDriverObject, PUNICODE_STRING pRegistryPath)
{int i = 0;NTSTATUS Status = STATUS_SUCCESS;for (i = 0; i < IRP_MJ_MAXIMUM_FUNCTION; i++){pDriverObject->MajorFunction[i] = DispatchPass;}pDriverObject->MajorFunction[IRP_MJ_READ] = DispatchRead;Status = MyAttachDevice(pDriverObject);if (!NT_SUCCESS(Status)){KdPrint(("AttachDevice ERROR!\n"));}else{KdPrint(("AttachDevice SUCCESS!\n"));}pDriverObject->DriverUnload = DriverUnload;return Status;
}

参考资料

Windows Driver Development Tutorial