IRP_MJ_WRITE to file mapping

Hi, Tony, greatest thanks for help.
At first place, i can’t to find out, which from all write
request is ‘my’. I’ve try to find out of this thing by
testing via MmGetSystemAddressForMdl(Irp->MdlAddress),
and subsequently looking up of contents of this buffer.
Unfortunately, but almost all Page I/O write requests are
becomes with Irp->UserBuffer field which equals NULL.
The IFS Kit FAQ at OSR site was describe of this case at
next manner: “The Irp->UserBuffer must have the same value
as is returned by MmGetMdlVirtualAddress. If it does not
and the underlying file system must break up the I/O
operation into a series of sub-operations, it will do so
incorrectly (see how this is handled in deviosup.c within
the FAT file system example in the IFS Kit, where it builds
a partial MDL using IoBuildPartialMdl.” Once again
unfortunately, but i have not of the IFS Kit. Do you can
help to me, and say what i may to handle of this case
and look up of the contents of buffer ?
Beforehand grateful to you