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IRP数据结构（即 I/O请求包数据结构）

IRP结构

图5-1显示了IRP的数据结构，阴影部分代表不透明域。下面是该结构中重要域的简要描述。

MdlAddress(PMDL)域指向一个内存描述符表(MDL)，该表描述了一个与该请求关联的用户模式缓冲区。如果顶级设备对象的Flags域为DO_DIRECT_IO，则I/O管理器为IRP_MJ_READ或IRP_MJ_WRITE请求创建这个MDL。如果一个IRP_MJ_DEVICE_CONTROL请求的控制代码指定METHOD_IN_DIRECT或METHOD_OUT_DIRECT操作方式，则I/O管理器为该请求使用的输出缓冲区创建一个MDL。MDL本身用于描述用户模式虚拟缓冲区，但它同时也含有该缓冲区锁定内存页的物理地址。为了访问用户模式缓冲区，驱动程序必须做一点额外工作。

图5-1. I/O请求包数据结构

Flags(ULONG)域包含一些对驱动程序只读的标志。但这些标志与WDM驱动程序无关。

AssociatedIrp(union)域是一个三指针联合。其中，与WDM驱动程序相关的指针是AssociatedIrp.SystemBuffer。SystemBuffer指针指向一个数据缓冲区，该缓冲区位于内核模式的非分页内存中。对于IRP_MJ_READ和IRP_MJ_WRITE操作，如果顶级设备指定DO_BUFFERED_IO标志，则I/O管理器就创建这个数据缓冲区。对于IRP_MJ_DEVICE_CONTROL操作，如果I/O控制功能代码指出需要缓冲区(见第九章)，则I/O管理器就创建这个数据缓冲区。I/O管理器把用户模式程序发送给驱动程序的数据复制到这个缓冲区，这也是创建IRP过程的一部分。这些数据可以是与WriteFile调用有关的数据，或者是DeviceIoControl调用中所谓的输入数据。对于读请求，设备驱动程序把读出的数据填到这个缓冲区，然后I/O管理器再把缓冲区的内容复制到用户模式缓冲区。对于指定了METHOD_BUFFERED的I/O控制操作，驱动程序把所谓的输出数据放到这个缓冲区，然后I/O管理器再把数据复制到用户模式的输出缓冲区。

IoStatus(IO_STATUS_BLOCK)是一个仅包含两个域的结构，驱动程序在最终完成请求时设置这个结构。IoStatus.Status域将收到一个NTSTATUS代码，而IoStatus.Information的类型为ULONG_PTR，它将收到一个信息值，该信息值的确切含义要取决于具体的IRP类型和请求完成的状态。Information域的一个公认用法是用于保存数据传输操作，如IRP_MJ_READ，的流量总计。某些PnP请求把这个域作为指向另外一个结构的指针，这个结构通常包含查询请求的结果。

RequestorMode将等于一个枚举常量UserMode或KernelMode，指定原始I/O请求的来源。驱动程序有时需要查看这个值来决定是否要信任某些参数。

PendingReturned(BOOLEAN)如果为TRUE，则表明处理该IRP的最低级派遣例程返回了STATUS_PENDING。完成例程通过参考该域来避免自己与派遣例程间的潜在竞争。

Cancel(BOOLEAN)如果为TRUE，则表明IoCancelIrp已被调用，该函数用于取消这个请求。如果为FALSE，则表明没有调用IoCancelIrp函数。取消IRP是一个相对复杂的主题，我将在本章的最后详细描述它。

CancelIrql(KIRQL)是一个IRQL值，表明那个专用的取消自旋锁是在这个IRQL上获取的。当你在取消例程中释放自旋锁时应参考这个域。

CancelRoutine(PDRIVER_CANCEL)是驱动程序取消例程的地址。你应该使用IoSetCancelRoutine函数设置这个域而不是直接修改该域。

UserBuffer(PVOID)对于METHOD_NEITHER方式的IRP_MJ_DEVICE_CONTROL请求，该域包含输出缓冲区的用户模式虚拟地址。该域还用于保存读写请求缓冲区的用户模式虚拟地址，但指定了DO_BUFFERED_IO或DO_DIRECT_IO标志的驱动程序，其读写例程通常不需要访问这个域。当处理一个METHOD_NEITHER控制操作时，驱动程序能用这个地址创建自己的MDL。

Tail.Overlay是Tail联合中的一种结构，它含有几个对WDM驱动程序有潜在用途的成员。图5-2是Tail联合的组成图。在这个图中，以水平方向从左到右是这个联合的三个可选成员，在垂直方向是每个结构的成员描述。Tail.Overlay.DeviceQueueEntry(KDEVICE_QUEUE_ENTRY)和Tail.Overlay.DriverContext(PVOID[4])是Tail.Overlayare内一个未命名联合的两个可选成员(只能出现一个)。I/O管理器把DeviceQueueEntry作为设备标准请求队列中的连接域。当IRP还没有进入某个队列时，如果你拥有这个IRP你可以使用这个域，你可以任意使用DriverContext中的四个指针。Tail.Overlay.ListEntry(LIST_ENTRY)仅能作为你自己实现的私有队列的连接域。

图5-2. IRP中Tail联合的组成图

CurrentLocation(CHAR)和Tail.Overlay.CurrentStackLocation(PIO_STACK_LOCATION)没有公开为驱动程序使用，因为你完全可以使用象IoGetCurrentIrpStackLocation这样的函数获取这些信息。但意识到CurrentLocation就是当前I/O堆栈单元的索引以及CurrentStackLocation就是指向它的指针，会对驱动程序调试有一些帮助。

I/O堆栈

任何内核模式程序在创建一个IRP时，同时还创建了一个与之关联的IO_STACK_LOCATION结构数组：数组中的每个堆栈单元都对应一个将处理该IRP的驱动程序，另外还有一个堆栈单元供IRP的创建者使用(见图5-3)。堆栈单元中包含该IRP的类型代码和参数信息以及完成函数的地址。图5-4显示了堆栈单元的结构。

图5-3. 驱动程序和I/O堆栈之间的平行关系

注意我将在本章稍后处讨论IRP的创建机制。将帮助你了解DEVICE_OBJECT的StackSize域，该域指出IRP应为其目标设备驱动程序保留多少堆栈单元。

图5-4. I/O堆栈单元数据结构

MajorFunction(UCHAR)是该IRP的主功能码。这个代码应该为类似IRP_MJ_READ一样的值，并与驱动程序对象中MajorFunction表的某个派遣函数指针相对应。如果该代码存在于某个特殊驱动程序的I/O堆栈单元中，它有可能一开始是，例如IRP_MJ_READ，而后被驱动程序转换成其它代码，并沿着驱动程序堆栈发送到低层驱动程序。我将在第十一章(USB总线)中举一个这样的例子，USB驱动程序把标准的读或写请求转换成内部控制操作，以便向USB总线驱动程序提交请求。

MinorFunction(UCHAR)是该IRP的副功能码。它进一步指出该IRP属于哪个主功能类。例如，IRP_MJ_PNP请求就有约一打的副功能码，如IRP_MN_START_DEVICE、IRP_MN_REMOVE_DEVICE，等等。

Parameters(union)是几个子结构的联合，每个请求类型都有自己专用的参数，而每个子结构就是一种参数。这些子结构包括Create(IRP_MJ_CREATE请求)、Read(IRP_MJ_READ请求)、StartDevice(IRP_MJ_PNP的IRP_MN_START_DEVICE子类型)，等等。

DeviceObject(PDEVICE_OBJECT)是与该堆栈单元对应的设备对象的地址。该域由IoCallDriver函数负责填写。

FileObject(PFILE_OBJECT)是内核文件对象的地址，IRP的目标就是这个文件对象。驱动程序通常在处理清除请求(IRP_MJ_CLEANUP)时使用FileObject指针，以区分队列中与该文件对象无关的IRP。

CompletionRoutine(PIO_COMPLETION_ROUTINE)是一个I/O完成例程的地址，该地址是由与这个堆栈单元对应的驱动程序的更上一层驱动程序设置的。你绝对不要直接设置这个域，应该调用IoSetCompletionRoutine函数，该函数知道如何参考下一层驱动程序的堆栈单元。设备堆栈的最低一级驱动程序并不需要完成例程，因为它们必须直接完成请求。然而，请求的发起者有时确实需要一个完成例程，但通常没有自己的堆栈单元。这就是为什么每一级驱动程序都使用下一级驱动程序的堆栈单元保存自己完成例程指针的原因。

Context(PVOID)是一个任意的与上下文相关的值，将作为参数传递给完成例程。你绝对不要直接设置该域；它由IoSetCompletionRoutine函数自动设置，其值来自该函数的某个参数。

The IRP structure is a partial opaquestructure that represents an I/O request packet. Drivers can usethe following members of the IRP structure.

typedef struct _IRP {
   PMDL   MdlAddress;
   ULONG   Flags;
    union{
     struct _IRP   *MasterIrp;
     .
     PVOID   SystemBuffer;
    }AssociatedIrp;
   .   .
   IO_STATUS_BLOCK   IoStatus;
   KPROCESSOR_MODE   RequestorMode;
    BOOLEANPendingReturned;
    .
    .
   BOOLEAN   Cancel;
   KIRQL   CancelIrql;

   PDRIVER_CANCEL   CancelRoutine;
    PVOIDUserBuffer;
    union{
     struct {
     .
     union {
       KDEVICE_QUEUE_ENTRY DeviceQueueEntry;
       struct {
         PVOID   DriverContext[4];
       };
     };
     .
     .
     PETHREAD   Thread;
     .
     .
     LIST_ENTRY   ListEntry;
     .
     .
     } Overlay;
    .
    .
    }Tail;
} IRP, *PIRP;

Members

MdlAddress

Pointer to an MDL describing a user buffer, if the driver isusing direct I/O, and the IRP majorfunction code is one of the following:

IRP_MJ_READ

The MDL describes an empty buffer that the device or driverfills in.

IRP_MJ_WRITE

The MDL describes a buffer that contains data for the device ordriver.

IRP_MJ_DEVICE_CONTROL or IRP_MJ_INTERNAL_DEVICE_CONTROL

If the IOCTL code specifies the METHOD_IN_DIRECT transfer type,the MDL describes a buffer that contains data for the device ordriver.

If the IOCTL code specifies theMETHOD_OUT_DIRECT transfer type, the MDL describes an empty bufferthat the device or driver fills in.

For more information about the buffersthat are associated with METHOD_IN_DIRECT and METHOD_OUT_DIRECTtransfer types in IOCTL codes, see Buffer Descriptions for I/O Control Codes.

If the driver is not using direct I/O,this pointer is NULL.

Flags

File system drivers use this field, which is read-only for alldrivers. Network and, possibly, highest-level device drivers alsomight read this field, which can be set with one or more of thefollowing system-defined masks:

IRP_NOCACHE
IRP_PAGING_IO
IRP_MOUNT_COMPLETION
IRP_SYNCHRONOUS_API
IRP_ASSOCIATED_IRP
IRP_BUFFERED_IO
IRP_DEALLOCATE_BUFFER
IRP_INPUT_OPERATION
IRP_SYNCHRONOUS_PAGING_IO
IRP_CREATE_OPERATION
IRP_READ_OPERATION
IRP_WRITE_OPERATION
IRP_CLOSE_OPERATION
IRP_DEFER_IO_COMPLETION

AssociatedIrp.MasterIrp

Pointer to the master IRP in an IRP that was created by ahighest-level driver's call to IoMakeAssociatedIrp.

AssociatedIrp.SystemBuffer

Pointer to a system-space buffer.

If the driver is using buffered I/O, the buffer'spurpose is determined by the IRP major function code, asfollows:

IRP_MJ_READ

The buffer receives data from the device or driver. Thebuffer's length is specified by Parameters.Read.Length in thedriver's IO_STACK_LOCATION structure.

IRP_MJ_WRITE

The buffer supplies data for the device or driver. The buffer'slength is specified by Parameters.Write.Length in the driver'sIO_STACK_LOCATION structure.

IRP_MJ_DEVICE_CONTROL or IRP_MJ_INTERNAL_DEVICE_CONTROL

The buffer represents both the input and output buffers thatare supplied to DeviceIoControl and IoBuildDeviceIoControlRe quest.Output data overwrites input data.

For input, the buffer's length isspecified by Parameters.DeviceIoControl.InputBufferLength in thedriver's IO_STACK_LOCATION structure.

For output, the buffer's length isspecified by Parameters.DeviceIoControl.OutputBufferLength in thedriver's IO_STACK_LOCATION structure.

For more information, see Buffer Descriptions for I/O Control Codes.

If the driver is using direct I/O, the buffer's purposeis determined by the IRP major function code, as follows:

IRP_MJ_READ

NULL.

IRP_MJ_WRITE

NULL.

IRP_MJ_DEVICE_CONTROL or IRP_MJ_INTERNAL_DEVICE_CONTROL

The buffer represents the input buffer that is supplied toDeviceIoControl and IoBuildDeviceIoControlRe quest.

The buffer's length is specified byParameters.DeviceIoControl.InputBufferLength in the driver'sIO_STACK_LOCATION structure.

For more information, see Buffer Descriptions for I/O Control Codes.

IoStatus

Contains the IO_STATUS_BLOCK structure in which a driverstores status and information before calling IoCompleteRequest.

RequestorMode

Indicates the execution mode of the original requester of theoperation, one of UserMode or KernelMode.

PendingReturned

If set to TRUE, a driver has marked the IRP pending. Each IoCompletion routine should check the value ofthis flag. If the flag is TRUE, and if the IoCompletion routinewill not return STATUS_MORE_PROCESSING_REQUIRED, the routine shouldcall IoMarkIrpPending to propagate the pending statusto drivers above it in the device stack.

Cancel

If set to TRUE, the IRP either is or should be canceled.

CancelIrql

Contains the IRQL at which a driver is running when IoAcquireCancelSpinLock is called.

CancelRoutine

Contains the entry point for a driver-supplied Cancel routine to be called if the IRP iscanceled. NULL indicates that the IRP is not currentlycancelable.

UserBuffer

Contains the address of an output buffer if the major functioncode in the I/O stack location is IRP_MJ_DEVICE_CONTROL or IRP_MJ_INTERNAL_DEVICE_CONTROL and the I/Ocontrol code was defined with METHOD_NEITHER.

Tail.Overlay.DeviceQueueEntry

If IRPs are queued in the device queue associated with thedriver's device object, this field links IRPs in the device queue.These links can be used only while the driver is processing theIRP.

Tail.Overlay.DriverContext

If IRPs are not queued in the device queue associated with thedriver's device object, this field can be used by the driver tostore up to four pointers. This field can be used only while thedriver owns the IRP.

Tail.Overlay.Thread

Is a pointer to the caller's thread control block. Higher-leveldrivers that allocate IRPs for lower-level removable-media driversmust set this field in the IRPs they allocate. Otherwise, the FSDcannot determine which thread to notify if the underlying devicedriver indicates that the media requires verification.

Tail.Overlay.ListEntry

If a driver manages its own internal queues of IRPs, it usesthis field to link one IRP to the next. These links can be usedonly while the driver is holding the IRP in its queue or isprocessing the IRP.

Headers

Defined in wdm.h and ntddk.h. Includewdm.h or ntddk.h.

Comments

Undocumented members of the IRPstructure are reserved, used only by the I/O manager or, in somecases, by FSDs.

An IRP is the basic I/O managerstructure used to communicate with drivers and to allow drivers tocommunicate with each other. A packet consists of two differentparts:

Header, or fixed part of the packet ? This is used by the I/Omanager to store information about the original request, such asthe caller's device-independent parameters, the address of thedevice object upon which a file is open, and so on. It is also usedby drivers to store information such as the final status of therequest.
I/O stack locations ? Following the header is a set of I/O stack locations, one per driver in the chainof layered drivers for which the request is bound. Each stacklocation contains the parameters, function codes, and context usedby the corresponding driver to determine what it is supposed to bedoing. For more information, see the IO_STACK_LOCATION structure.

While a higher-level driver might checkthe value of the Cancel Boolean in an IRP, that driver cannotassume the IRP will be completed with STATUS_CANCELLED by alower-level driver even if the value is TRUE.

IRP数据结构（即 I/O请求包数据结构）

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