forwarding read request from Function driver to Bus driver

NTDEV
1

Hi All,

This is regarding KMDF drivers.

I used toaster example to build a Bus driver(KMDF) which is a FDO for my hardware. I have a KMDF function driver which has to alter the read request which it gets and should pass it to parent FDO (bus driver). From there i have to format it and send it to my device.

How can i do that ?

I see “WdfRequestCopyCurrentStackLocationToNext” function is not available now, which i found in one of the Microsoft presentationm which i think might have helped me to pass it down the stack.
Corret me if i am wrong,
PDO is the bottom of device stack so i have to pass this request to PDO first and from there i should pass it to parent FDO.

I couldn’t find any example in DDK which does this.

Regards,
Supreet

2

To send an IRP, modified, down the stack:
WdfDeviceGetIoTarget - to get the I/O target of the PDO for a FDO.
WdfIoTargetFormatRequestFor* - to format the IRP.
WdfRequestSend - to send the IRP to the PDO.

Also see in the WDK KMDF docs:
Handling I/O Requests in Framework-based Drivers -> Framework Request Objects -> Processing I/O Requests -> Forwarding I/O Requests
Using I/O Targets -> General I/O Targets

Regarding sending the IRP from the PDO to the bus driver’s FDO: are you sure this is necessary? Remember that the bus driver’s FDO and the end device’s PDO are in the same driver, even though they are in different device stacks. I think forwarding IRPs to the bus driver’s FDO is generally unncessary, since you can just synchronize and access the hardware directly from the PDO.

But if you really want to:
Use the PDO’s context to store a handle to the bus driver’s FDO.
WdfDeviceWdmGetDeviceObject, WdfIoTargetCreate, WDF_IO_TARGET_OPEN_PARAMS_INIT_EXISTING_DEVICE, WdfIoTargetOpen - to get the I/O target for the bus driver’s FDO from one of its PDOs.
WdfIoTargetFormatRequestFor* - to format the IRP.
WdfRequestSend - to send the IRP to the bus driver FDO.

Remember you have to either have to register for a completion routine or use the “send and forget” flag.

-Stephen Cleary

3

The DDI was renamed to WdfRequestFormatRequestUsingCurrentType- I believe this was to stress a WDF model of “formatting” requests for a purpose as opposed to a WDM concept of “stack locations”.

There is a discussion of request forwarding in the WDK (probably even more in the book).

-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of xxxxx@indiatimes.com
Sent: Friday, June 15, 2007 4:57 AM
To: Windows System Software Devs Interest List
Subject: [ntdev] forwarding read request from Function driver to Bus driver

Hi All,

This is regarding KMDF drivers.

I used toaster example to build a Bus driver(KMDF) which is a FDO for my hardware. I have a KMDF function driver which has to alter the read request which it gets and should pass it to parent FDO (bus driver). From there i have to format it and send it to my device.

How can i do that ?

I see “WdfRequestCopyCurrentStackLocationToNext” function is not available now, which i found in one of the Microsoft presentationm which i think might have helped me to pass it down the stack.
Corret me if i am wrong,
PDO is the bottom of device stack so i have to pass this request to PDO first and from there i should pass it to parent FDO.

I couldn’t find any example in DDK which does this.

Regards,
Supreet

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4

Hi Stephen and Bob,

Thanks for the quick response, I did the same thing as Stephen has explained,how to pass IRP down the stack, and i was expecting it to come to my Bus driver FDO, Guess the problem was i was trying to do this on Friday evening in office ;-), Now i know how it works Thanks Bob for clarifying about the DDI, I will let you guys know how things went on. Thanks again guys.

Regards,
Sup

5

Well just forwarding it down your stack is going to send it to your bus
driver PDO, not your bus driver FDO. Your bus driver FDO is in a separate
stack.

  • Jake Oshins

wrote in message news:xxxxx@ntdev…
> Hi Stephen and Bob,
>
> Thanks for the quick response, I did the same thing as Stephen has
> explained,how to pass IRP down the stack, and i was expecting it to come
> to my Bus driver FDO, Guess the problem was i was trying to do this on
> Friday evening in office ;-), Now i know how it works Thanks Bob for
> clarifying about the DDI, I will let you guys know how things went on.
> Thanks again guys.
>
> Regards,
> Sup
>
>