From: Maxim S. Shatskih [maxim@storagecraft.com]
Sent: Sunday, June 04, 2000 6:18 PM
To: NT Developers Interest List
Subject: [ntdev] Re: ZWwriteFile

Try:
- creating a file with preallocated size from ZwCreateFile or user mode
CreateFile + MoveFilePointer + SetEndOfFile.
- then use FSCTL_GET_RETRIEVAL_POINTERS to get the disk sector
numbers covered by the file.
- then work with the disk driver directly, bypassing the FSD.

Note that FSCTL_GET_RETRIEVAL_POINTERS cannot be called from
kmode directly - at least on NT4. The filesystems use ProbeForWrite function
to test the IOCTL's buffer - and this function will fail if this buffer will
be in the
kmode address space.

You can use a trick to bypass it:
- ZwCreateSection not based on any file (pagefile-based).
- ZwMapViewOfSection for this section while being in a System process
context (you can use, for instance, ExQueueWorkItem callbacks - they are
executed in System process).
- this will allocate memory _in System process's usermode address space_.
This memory is accessible from kmode - you can reference it directly and
even without try/catch blocks provided you have specified the valid
address -
this memory is private for your driver and nobody else knows on it.

BTW - this is a good way if you want to allocate several megabytes of
pageable memory in your driver.

    Max

----- Original Message -----
From: <Mika.Piirainen@patria.fi>
To: NT Developers Interest List <ntdev@lists.osr.com>
Sent: Wednesday, May 31, 2000 1:59 PM
Subject: [ntdev] ZWwriteFile


> Hi
> I need write to file data 10 Mbit/s from PCI card. Data is 32 bit numbers
and i
> want write those numbers to HD. Can anybody tell what is a efficient way
to do
> this. Is there other/better ways than  ZWwriteFile to do this operation.
>
>
> Best regards
>
> Mika Piirainen
> Patria Oy
>
>
>
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