From - Wed Sep 24 08:06:24 1997
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From: jeh@cmkrnl.com (Jamie Hanrahan)
Newsgroups: comp.os.ms-windows.programmer.nt.kernel-mode
Subject: Re: ISR can't access User buffer HELP!!!!!
Message-ID: <1997Sep23.183801.8219@cmkrnl>
Date: 23 Sep 97 18:38:01 PST
References: <34283caf.349039037@news.connectnet.com>
Organization: Kernel Mode Systems, San Diego, CA
Lines: 25

In article <34283caf.349039037@news.connectnet.com>, jvasquez@getntds.com writes:
> The device was created using the flag DO_DIRECT_IO when IoCreateDevice
> was called.
> 
> Doing the processing of the IRP_MJ_WRITE, I get the user's buffer
> address from the Irp->MdlAddress. and store it in the device
> extension. 

Irp->MdlAddress is not the user's buffer address.  It is the address
of an intermediate structure (an MDL) that describes the physical
memory location(s) of the user's buffer. 

To get an address that is usable in arbitrary thread context, you must 
call MmGetSystemAddressForMdl(Irp->MdlAddress).  You must do this in 
the context of the requesting thread (ie in the dispatch routine that 
handles the IRP).  You can then use the returned value from 
MmGetSystemAddressForMdl at any time until you call IoCompleteRequest 
on the IRP. 

	--- Jamie Hanrahan, Kernel Mode Systems, San Diego CA
        Internet: jeh@cmkrnl.com (JH645)  CompuServe: 74140,2055  
drivers, internals, networks, applications, and training for VMS and Windows NT
NT driver FAQ, links, and other information:  http://www.cmkrnl.com/

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