求教,urb = USBD_CreateConfigurationRequestEx(Descriptors,ilist);

为什么第一次调用urb = USBD_CreateConfigurationRequestEx(Descriptors,ilist);时能成功的返回，但第二次却返回失败。

/////////////////////////////////////////////////////////////////////////////////
// UsbSelectConfiguration: Select first config
/////////////////////////////////////////////////////////////////////////////////
NTSTATUS UsbSelectConfiguration(IN PDEVICE_EXTENSION dx)
{
// Get all first configuration descriptors
PUSB_CONFIGURATION_DESCRIPTOR Descriptors = NULL;

ULONG size;
NTSTATUS status;
PUSB_INTERFACE_DESCRIPTOR id;
USBD_INTERFACE_LIST_ENTRY ilist[2];
PURB urb;
PUSBD_INTERFACE_INFORMATION InterfaceInfo;
PUSBD_PIPE_INFORMATION pi;

dx->UsbPipeHandle = NULL;

    Descriptors = dx->UsbConfigurationDescriptor;
/*
status = UsbGetConfigurationDescriptors(dx,Descriptors,0,&size);
if( !NT_SUCCESS(status))
{
DebugPrint(\"UsbGetConfigurationDescriptors failed = 0x%x\", status);
FreeIfAllocated(Descriptors);
return status;
}
*/
// FreeIfAllocated(Descriptors);
//    DebugPrint(\"USB Configuration Descriptor size=0x%x(%d)\\n\",size,size);
    DebugPrint(\"USB Configuration Descriptor\\n\");
    DebugPrint(\"-------------------------------------------------------\\n\");
    DebugPrint(\"bLength             = 0x%x(%d)\\n\", Descriptors->bLength,Descriptors->bLength);
    DebugPrint(\"bDescriptorType     = 0x%x\\n\", Descriptors->bDescriptorType);
    DebugPrint(\"wTotalLength        = 0x%x\\n\", Descriptors->wTotalLength);
    DebugPrint(\"bNumInterfaces      = 0x%x\\n\", Descriptors->bNumInterfaces);
    DebugPrint(\"bConfigurationValue = 0x%x\\n\", Descriptors->bConfigurationValue);
    DebugPrint(\"iConfiguration      = 0x%x\\n\", Descriptors->iConfiguration);
    DebugPrint(\"bmAttributes        = 0x%x\\n\", Descriptors->bmAttributes);
    DebugPrint(\"MaxPower            = 0x%x,(%d mA)\\n\", Descriptors->MaxPower,Descriptors->MaxPower);

// Search for an interface Number = 0x81
/*
//searches a given configuration descriptor and
//returns a pointer to an interface that matches the given search criteria.

 USBD_ParseConfigurationDescriptorEx(
       //Points to a USB configuration descriptor that contains the interface for which to search
       IN PUSB_CONFIGURATION_DESCRIPTOR  ConfigurationDescriptor,

       //Points to the address within the configuration descriptor, provided at ConfigurationDescriptor, to begin searching from
       IN PVOID  StartPosition,

       //Specifies the device-defined index of the interface to be retrieved
       IN LONG InterfaceNumber,

       //Specifies the device-defined alternate-setting index of the interface to be retrieved
       IN LONG AlternateSetting,

       //Specifies the device- or USB-defined identifier for the interface class of the interface to be retrieved.
       IN LONG InterfaceClass,

       //Specifies the device- or USB-defined identifier for the interface subclass of the interface to be retrieved.
       IN LONG InterfaceSubClass,

       //Specifies the device- or USB-defined identifier for the interface protocol of the interface to be retrieved// Search for a HID device, boot protocol, keyboard
       IN LONG InterfaceProtocol
       );
*/

id = USBD_ParseConfigurationDescriptorEx(Descriptors,
Descriptors,
-1,
-1,
0x03,  
-1,  
-1);
if(id==NULL)
{
DebugPrintMsg(\"No matching interface found\");

FreeIfAllocated(Descriptors);
return STATUS_NO_SUCH_DEVICE;
}

// Build list of interfaces we are interested in
ilist[0].InterfaceDescriptor = id;
ilist[0].Interface = NULL; // Will point to urb->UrbUsbSelectConfiguration.Interface
ilist[1].InterfaceDescriptor = NULL;

DebugPrintMsg(\"Selecting configuration\");

// Create select configuration URB
urb = USBD_CreateConfigurationRequestEx(Descriptors,ilist);
status = CallUSBDI(dx, urb,IOCTL_INTERNAL_USB_SUBMIT_URB,0);
if(!NT_SUCCESS(status) || !USBD_SUCCESS( urb->UrbHeader.Status))
{
DebugPrint(\"Selecting configuration Error status=0x%x URB_status=0x%x\", status, urb->UrbHeader.Status);
status = STATUS_UNSUCCESSFUL;
}
else
{
// Select config worked
DebugPrintMsg(\"Select configuration worked\");
dx->UsbConfigurationHandle = urb->UrbSelectConfiguration.ConfigurationHandle;

// Find pipe handle of first pipe, ie interrupt pipe that returns input HID reports
InterfaceInfo = &urb->UrbSelectConfiguration.Interface;
DebugPrint(\"interface Class = %d ,NumberOfPipes = %d\\n\", InterfaceInfo->Class, InterfaceInfo->NumberOfPipes);
if(InterfaceInfo->NumberOfPipes>0)
{
pi = &InterfaceInfo->Pipes[0];
dx->UsbPipeHandle = pi->PipeHandle;

DebugPrint(\"PipeHandle = 0x%x\\n\", dx->UsbPipeHandle);
DebugPrint(\"Pipes[0] EndpointAddress = 0x%2x Interval = %dms PipeType = %d MaximumTransferSize = %d\\n\",
pi->EndpointAddress, pi->Interval, pi->PipeType, pi->MaximumTransferSize);
}

if(dx->UsbPipeHandle==NULL)
status = STATUS_UNSUCCESSFUL;
}

FreeIfAllocated(urb);

return status;
}