Mail Archives: djgpp/2000/04/10/03:45:05

From: "Wojciech Galazka" <wojciech DOT galazka AT polkomtel DOT com DOT pl>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: fstat works incorrectly under Windows NT
Date: Mon, 10 Apr 2000 09:43:58 +0200
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To: djgpp AT delorie DOT com
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Eli Zaretskii wrote...
>On Sat, 8 Apr 2000, Wojciech Galazka wrote:
>> The
>> newest version of LFN  I'm working on completely bypasses int 21h AX=6Ch
>> call and creates/opens files using Win32 CreateFile() call. It turns out
>> that DOS file handles returned by the LFN driver under some circumstances
>> are not recognized by int 21h, AX=4400h used by get_dev_info() call.
>> returns 0 instead.
>Is bypassing the DOS calls a good idea?  How do you get a handle from
>CreateFile that can be used in various DOS calls, such as 214400?
>The handle you return must be a valid DOS handle, otherwise lots of
>things will subtly break.

Bypassing the DOS calls is not a good idea but it works fast . Basically
long filename is translated into short filename by the driver and then DOS
creates/opens the file using the short filename.
As you pointed out the handle returned by CreateFile() needs to be
translated into a DOS file handle, this can be done using some undocumented
calls to NTVDM.  The good news is that it works faster than using int 21h,
the bad news is that there are problemns with opening devices (like NUL) and
some DOS calls don't work with that handles (as in the case with int 21h,
I put aside this promising but not yet working approach and reverted to
handling create/open files using DOS. This way I don't need to worry about
SFT , or the like. Perhaps I should wait until DoJ case against Microsoft
ends up with Windows source code being released. :)

>> I'm working on this right now and wonder if the SFT layout under Windows
>> is anywhere documented ....
>What SFT do you have in mind?  If that's the SFT for the DOS box, I'm
>not even sure NTVDM creates it.

According to Schulman's "Undocumented DOS" there is some rudimentary SFT
structure but it is different from the one used by DOS 5.

BTW Could you suggest any texts of how DPMI serwer works?. All I know is
that for a DOS 32 bit DPMI  program a LDT is created by DPMI server
somewhere by NTVDM. It is probably possible to access that LDT from DPMI
server side. But how to free a descriptor not used anymore by a program? The
bugs in DPMI server make it very annoying to compile large DJGPP packages.


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