WdfUsbTargetPipeReadSynchronously method

[Applies to KMDF and UMDF]

The WdfUsbTargetPipeReadSynchronously method builds a read request and sends it synchronously to a specified USB input pipe.

Syntax

NTSTATUS WdfUsbTargetPipeReadSynchronously(
  [in]             WDFUSBPIPE Pipe,
  [in, optional]   WDFREQUEST Request,
  [in, optional]   PWDF_REQUEST_SEND_OPTIONS RequestOptions,
  [in, optional]   PWDF_MEMORY_DESCRIPTOR MemoryDescriptor,
  [out, optional]  PULONG BytesRead
);

Parameters

Pipe [in]

A handle to a framework pipe object that was obtained by calling WdfUsbInterfaceGetConfiguredPipe.

Request [in, optional]

A handle to a framework request object. This parameter is optional and can be NULL. For more information, see the following Remarks section.

RequestOptions [in, optional]

A pointer to a caller-allocated WDF_REQUEST_SEND_OPTIONS structure that specifies options for the request. This pointer is optional and can be NULL. For more information, see the following Remarks section.

MemoryDescriptor [in, optional]

A pointer to a caller-allocated WDF_MEMORY_DESCRIPTOR structure that describes the buffer that will receive data from the device. The buffer size must be a multiple of the pipe's maximum packet size unless the driver has called WdfUsbTargetPipeSetNoMaximumPacketSizeCheck. For more information about this buffer, see the following Remarks section.

BytesRead [out, optional]

A pointer to a location that receives the number of bytes that were read, if the operation succeeds. This parameter is optional and can be NULL.

Return value

WdfUsbTargetPipeReadSynchronously returns the I/O target's completion status value if the operation succeeds. Otherwise, this method can return one of the following values:

This method also might return other NTSTATUS values.

A bug check occurs if the driver supplies an invalid object handle.

Remarks

Use the WdfUsbTargetPipeReadSynchronously method to send read requests synchronously. To send read requests asynchronously, use WdfUsbTargetPipeFormatRequestForRead, followed by WdfRequestSend.

The pipe that the Pipe parameter specifies must be an input pipe, and the pipe's type must be WdfUsbPipeTypeBulk or WdfUsbPipeTypeInterrupt.

The WdfUsbTargetPipeReadSynchronously method does not return until the request has completed, unless the driver supplies a time-out value in the WDF_REQUEST_SEND_OPTIONS structure that the RequestOptions parameter points to, or unless an error is detected.

You can forward an I/O request that your driver received in an I/O queue, or you can create and send a new request. In either case, the framework requires a request object and some buffer space.

To forward an I/O request that your driver received in an I/O queue:

1. Specify the received request's handle for the Request parameter.

2. Use the received request's output buffer for the WdfUsbTargetPipeReadSynchronously method's MemoryDescriptor parameter.

   The driver must call WdfRequestRetrieveOutputMemory to obtain a handle to a framework memory object that represents the request's output buffer and then place that handle in the WDF_MEMORY_DESCRIPTOR structure that MemoryDescriptor points to.

For more information about forwarding an I/O request, see Forwarding I/O Requests.

Drivers often divide received I/O requests into smaller requests that they send to an I/O target, so your driver might create new requests.

To create a new I/O request:

1. Supply a NULL request handle in the WdfUsbTargetPipeReadSynchronously method's Request parameter, or create a new request object and supply its handle:

   • If you supply a NULL request handle, the framework uses an internal request object. This technique is simple to use, but the driver cannot cancel the request.
   • If you call WdfRequestCreate to create one or more request objects, you can reuse these request objects by calling WdfRequestReuse. This technique enables your driver's EvtDriverDeviceAdd callback function to preallocate request objects for a device. Additionally, another driver thread can call WdfRequestCancelSentRequest to cancel the request, if necessary.

   Your driver can specify a non-NULL RequestOptions parameter, whether the driver provides a non-NULL or a NULL Request parameter. You can, for example, use the RequestOptions parameter to specify a time-out value.

2. Provide buffer space for the WdfUsbTargetPipeReadSynchronously method's MemoryDescriptor parameter.

   Your driver can specify this buffer space as a locally allocated buffer, as a WDFMEMORY handle, or as an MDL. You can use whichever method is most convenient.

   If necessary, the framework converts the buffer description to one that is correct for the I/O target's method for accessing data buffers.

   The following techniques are available:

   • Supply a local buffer

     Because WdfUsbTargetPipeReadSynchronously handles I/O requests synchronously, the driver can create request buffers that are local to the calling routine, as the following code example shows.

     Copy

     
     WDF_MEMORY_DESCRIPTOR  memoryDescriptor;
     MY_BUFFER_TYPE  myBuffer;
     WDF_MEMORY_DESCRIPTOR_INIT_BUFFER(&memoryDescriptor,
                                       (PVOID) &myBuffer,
                                       sizeof(myBuffer));
     
     

   • Supply a WDFMEMORY handle

     Call WdfMemoryCreate or WdfMemoryCreatePreallocated to obtain a handle to framework-managed memory, as the following code example shows.

     Copy

     
     WDF_MEMORY_DESCRIPTOR  memoryDescriptor;
     WDFMEMORY  memoryHandle = NULL;
     status = WdfMemoryCreate(NULL,
                              NonPagedPool,
                              POOL_TAG,
                              MY_BUFFER_SIZE,
                              &memoryHandle,
                              NULL);
     WDF_MEMORY_DESCRIPTOR_INIT_HANDLE(&memoryDescriptor,
                                       memoryHandle,
                                       NULL);
     
     

     Alternatively, the driver can call WdfRequestRetrieveOutputMemory to obtain a handle to a framework memory object that represents a received I/O request's output buffer, if you want the driver to pass that buffer's contents to the I/O target. The driver must not complete the received I/O request until the new request that WdfUsbTargetPipeReadSynchronously sends to the I/O target has been deleted, reused, or reformatted. (WdfUsbTargetPipeReadSynchronously increments the memory object's reference count. Deleting, reusing, or reformatting a request object decrements the memory object's reference count.)

   • Supply an MDL

     Drivers can obtain the MDL that is associated with a received I/O request by calling WdfRequestRetrieveOutputWdmMdl.

The framework sets the USBD_SHORT_TRANSFER_OK flag in its internal URB. Setting this flag allows the last packet of a data transfer to be less than the maximum packet size.

A driver cannot call WdfUsbTargetPipeReadSynchronously if it has configured a continuous reader for the pipe.

For information about obtaining status information after an I/O request completes, see Obtaining Completion Information.

For more information about the WdfUsbTargetPipeReadSynchronously method and USB I/O targets, see USB I/O Targets.

Examples

The following code example creates a framework memory object, initializes a WDF_MEMORY_DESCRIPTOR structure, and passes the structure to WdfUsbTargetPipeReadSynchronously. This example specifies NULL for the request object handle, so the framework will create a new request object for the I/O target.

WDFMEMORY  wdfMemory;
WDF_MEMORY_DESCRIPTOR  readBufDesc;
ULONG  BytesRead;

status = WdfMemoryCreate(
                         WDF_NO_OBJECT_ATTRIBUTES,
                         NonPagedPool,
                         0,
                         readSize,
                         &wdfMemory,
                         NULL
                         );
if (!NT_SUCCESS(status)){
    return ;
}

buffer = WdfMemoryGetBuffer(
                            wdfMemory,
                            NULL
                            );

WDF_MEMORY_DESCRIPTOR_INIT_BUFFER(
                                  &readBufDesc,
                                  buffer,
                                  readSize
                                  );

status = WdfUsbTargetPipeReadSynchronously(
                                           Pipe,
                                           NULL,
                                           NULL,
                                           &readBufDesc,
                                           &BytesRead
                                           );

Requirements

See also

WDF_MEMORY_DESCRIPTOR_INIT_BUFFER

WdfMemoryCreate

WdfUsbTargetPipeGetInformation

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