Everhart, Glenn
From:	Rob Green [robg@sundial.net]
Sent:	Monday, November 09, 1998 10:55 PM
To:	ntdev@atria.com
Subject:	[ntdev] NT writing back to file it is reading
Hello,
   I've come across a rather odd problem.  I have a disk driver that NTFS
calls to read data.  So far so good, i read the request data from another
device (that isn't in control by any other driver)  , and alls well.  as a
test i started copying a 100MB file (using copy file /b nul) after about 10
MB i start getting writes to the file that is being copied!  I have even
opened the file in read only mode and it still does it.  I have tracked it
done to my call to read the data from the raw hard drive. (not a fdisk
format)  I use IoBuildSyncRequest to create the irp to send to the driver.
from the pseudo code below you can see that i call MmGetSystemAddressForMdl
then call IoBuildSync on the resulting buffer.  I think this is where the
problem is, as IoBuildSync is going to generate another Mdl for the buffer,
so now i have 2 mdls(the one from the Irp, and the newly created one) and 2
systems addresses (the users buffer, and the system buffer)  Am i right in
that this could be my problem?  I tried creating an irp using the original
Irp, but it always BugChecks in KiInsertDeviceQueueAPC (or something
similar)  I have check the Irp APC fields and they are all null.  i used
IoAllocateIrp with a completion routine(bugcheck), and allocing my own with
a completion routine.  The completion routine is executed, but after it
returns my main code is never restarted. (yes i return
STATUS_MORE_PROCESSING_REQUIRED)  If i check to see what file is being
read, and don't call the ReadDataFromDrive routine on it, no writes occur
to the file.

Thanks

ReadDataFromDrive()
{
    Irp = IoBuildSynchronousRequest(...);
    if(Irp) {
        IoCallDriver(DeviceObject,Irp);
    }
}

DriverEntry(DeviceObject,Irp)
{
    Buffer = MmGetSystemAddressForMdl(Irp->MdlAddress);
    ntStatus = ReadDataFromDrive(
        DevExt,
        &ByteOffset,
        Stack->Parameters.Read.Length,
        Buffer);   
    ntStatus = DoPostProcessingOnData(
        DevExt,
        &ByteOffset,
        Stack->Parameters.Read.Length,
        Buffer);
    Irp->IoStatus.Status = ntStatus;
    Irp->IoStatus.Information = Stack->Parameters.Read.Length;
    IoCompleteRequest(Irp,IO_DISK_INCREMENT);
}
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