PF>anyone has any glimmer of
PF>an idea of how to find the address of the first 
PF>device driver header,please
PF>let me know.

 BL> I've been tearing my bedroom apart.  I have a torn sheet of paper with

I think i've got all the info I need.  For your notes:


 Area Os2prog, Msg#810, Jan-07-95 01:50:44
    From: Mike Bilow
      To: Peter Fitzsimmons
 Subject: device driver chain

 Yes, but you're treading on very thin ice to do it.  You need to get the word
 at 0070:0020h, which is the offset of the first device driver header (for the
 "NUL" device), also in segment 0070h (which is the "System
Anchor Segment").
 You need to have Ring 0 privilege to get access to segment 0070h.  I've never
 dared to do this inside a device driver, although it has worked consistently
 from the kernel debugger since about OS/2 1.2 or so.

 If all you want is a list of the character pseudo-devices, and you want it
 from Ring 3 code, DosQueryFSAttach() provides a documented method to get it.

 ------------------------------------------------------------------------------

 Area Os2prog, Msg#873, Jan-09-95 05:02:10
    From: Nick Mann
      To: Peter Fitzsimmons
 Subject: device driver chain

 I had to think about this one for a few minutes.  I knew I had some
 code somewhere that did this very thing, but couldn't remember where it
 was.  (I'm convinced old code is like old pens.  Given half a chance
 they slope off to a dark corner when you're not watching.  (-: )

 Anyway, in the October 1990 edition of Dr. Dobb's Journal, the article
 "Opening OS/2's Backdoor" described a device-driver/application couplet
 which did just what you are looking for.

 The device driver basically allows DevHlp functions to be executed by
 the application through IOCtl calls.  The application produces a list
 of installed devices.  The loop looking for the start of the chain is
 shown below:

 // locate the first driver
 selDriver = 0x50;                       // global data segment
 usOffsetDriver = 0;
 usBytesLeft = 32000;                    // should be large enough
 pchGlobal = MAKEP(MakeSel(selDriver), usOffsetDriver);
 do {
     PCH pchMatch;

     pchMatch = memchr(pchGlobal + 1, 'N', usBytesLeft);   // look for first
 char
     if(pchMatch == NULL) {                  // if no match
         ReleaseSel(SELECTOROF(pchGlobal));  // release the selector
         puts("NUL driver not found");       // and give up
         exit(1);
     }   // if no match

     // partial match
     usBytesLeft -= pchMatch - pchGlobal;  // reduce residual count
     pchGlobal = pchMatch;                 // point to start of match
 } while(memcmp(pchGlobal,                 // break out if name matches
                szNullDriver,              // exactly
                sizeof szNullDriver -1) != 0);


 ------------------------------------------------------------------------------

 From the DUDE bbs guys:

 You could try the following commands from the Kernel Debugger
    .d dev nuldev
 This lists the first installable device driver header. The DevNext field
 will point to the next device driver and you chain through all the installed
 drivers. On executing this command on the debug terminal you have the
 following output :

        DevNext  : 0400:0cd4
    .d dev #(0400:cd4)

 This yields the Device Header of the next Device. You could chain through
 other installed drivers through the DevNext field of the Header.

 The other alternative to chain through the device headers would be to us the
 following commands from the debug terminal,

   ##dw 70:20 l1    ;device chain starts at 70:20
   0070:00000020   0cb9
   ##dw 70:cb9
   0070:00000cb9   0cd4 0400
   ##.d dev 400:0cd4   yields the device header

 Ensure you have the same level of the Debug Kernel as the Retail Kernel
 before trying out the above commands from the Debug Terminal. For Base
 device Drivers use .d dev oemdev.



--- Maximus/2 2.01