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From: "SHG" <sgullach@ramtex.dk>
Newsgroups: comp.os.ms-windows.programmer.nt.kernel-mode
Subject: Re: how do you do fast i/o
Date: Tue, 2 Dec 1997 19:11:31 +0100
Lines: 98
Message-ID: <661j3s$mcq$1@mail-in1.inet.tele.dk>
References: <01bcfe5b$671d8c40$3c66ec84@cu-dialup.cornell.edu>
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 Hi
I have used this code from Art Baker

#ifdef DIRECT_IO
 /* These are the two undocumented calls that we will use to give the
calling
  * process I/O access. Ke386IoSetAccessMap() copies the passed map to the
TSS.
  *  Ke386IoSetAccessProcess() adjusts the IOPM offset pointer so that the
newly
  * copied map is actually used.  Otherwise, the IOPM offset points beyond
the
  * end of the TSS segment limit, causing any I/O access by the user-mode
  * process to generate an exception. */
 extern "C" void Ke386SetIoAccessMap(int, IOPM *); // 1 copy buffer, 0 fill
with 0xFF
 extern "C" void Ke386QueryIoAccessMap(int, IOPM *); // 1 copy buffer, 0
fill with 0xFF
 extern "C" void Ke386IoSetAccessProcess(PEPROCESS, int); // 1 enable IO, 0
disable IO
#endif

This code is in the DispatchOpen
#ifdef DIRECT_IO
 // Alter NT IO map so app on ring 3 can do IO
 if( pDeviceExtension->fDirectIO != 0 )
 {
  IOPM *pIOPM; // pointer to IO protection map

  pIOPM = (IOPM*)MmAllocateNonCachedMemory(sizeof(IOPM));
  if(pIOPM == NULL)
  {
   hwioRegDebug( L"DispatchCreate", (USHORT)0xFF, L"Direct IO NOT set" );
   Status = STATUS_INSUFFICIENT_RESOURCES;
  }
  else
  {
   hwioRegDebug( L"DispatchCreate",
(USHORT)pDeviceExtension->NtDeviceNumber, L"Direct IO set" );
   Ke386QueryIoAccessMap(1, pIOPM); // 1 copy buffer, 0 fill with 0xFF

   // Alter IO bits
   USHORT PortFirst = (USHORT)(pDeviceExtension->IntelPortBase);
   USHORT PortLast =
(USHORT)(pDeviceExtension->IntelPortBase+pDeviceExtension->PortCount);
//hwioRegDebug( L"DispatchCreate port first",
(USHORT)pDeviceExtension->NtDeviceNumber, (ULONG)PortFirst );
//hwioRegDebug( L"DispatchCreate port last",
(USHORT)pDeviceExtension->NtDeviceNumber, (ULONG)PortLast );
   for( USHORT p=PortFirst; p<PortLast; p++ )
   {
    (*(pIOPM))[p/8] &= (UCHAR)(0xFF7F>>(p%8));
   }

   Ke386IoSetAccessProcess(PsGetCurrentProcess(), 1); // 1 enable IO, 0
disable IO
   Ke386SetIoAccessMap(1, pIOPM ); // 1 copy buffer, 0 fill with 0xFF

   MmFreeNonCachedMemory( pIOPM, sizeof(IOPM) );
  }
 }
 else
  hwioRegDebug( L"DispatchCreate", (USHORT)pDeviceExtension->NtDeviceNumber,
L"Direct IO disabled" );
#endif

This code is in DispatchClose
#ifdef DIRECT_IO
 PDEVICE_EXTENSION pDeviceExtension =
(PDEVICE_EXTENSION)pDeviceObject->DeviceExtension;

 if( pDeviceExtension->fDirectIO != 0 )
 {
  hwioRegDebug( L"DispatchClose", (USHORT)pDeviceExtension->NtDeviceNumber,
L"Direct IO removed" );
  Ke386IoSetAccessProcess(PsGetCurrentProcess(), 0); // 1 enable IO, 0
disable IO
 }
#endif

Søren Gullach
SGullach@ramtex.dk


John Landau wrote in article
<01bcfe5b$671d8c40$3c66ec84@cu-dialup.cornell.edu>...

>Hi,
>     I think it was Art Baker in his The Windows NT Device Driver Book
>who said that for highest performance I/O you'd make the I/O page
>accessible to user-mode code.
>    How is this done? Are there any books on NT Device Drivers that
>address this and/or other optimization issues?
>     Regards,
>     John
>