Dear SCO Customer,

The enclosed Support Level Supplement (SLS) UOD370A (Sdsk Update 1.0)
resolves system panics due to memory corruption caused by SCSI disk
scatter/gather during raw I/O.

In order to install this SLS you must be running SCO UNIX System Release 3.2
Operating System Version 4.0 with Maintenance Supplement Version 4.1 or SCO 
Open Desktop Release 2.0.

See section III for a description and list of functional components.

SLS UOD370A consists of a custom installable diskette to be installed after
the operating system is loaded.

I. Installation

To install SLS UOD370A on an existing operating system using custom(ADM), 
take the following steps:

1.   If the system is running in multiuser mode, log in as root 
     on the console and, after warning other users that the system 
     will be down for some time, enter the command:

          shutdown -y -g0

     The system will then execute a controlled shutdown operation 
     which will display the following message when the shutdown 
     process is complete:

                 **   Safe to Power Off   **
                              or
              **   Press Any Key to Reboot   **


2.   Reboot the system.

3.   When the system reboots, you will see the message:

        Type CONTROL-d to proceed with normal startup,
       (or give root password for system maintenance):

     Enter the root password and press <Enter>.
     Wait until the "#" prompt appears.

4.   Next, insert the SLS diskette in the floppy drive and enter
     the command:
     
               /etc/custom

     The custom menu will appear.

5.   To select the following, use the arrow keys to highlight it
     and press <Enter>:

               Install -> A New Product -> Entire Product

     -    Position the cursor so that 'Install' is highlighted
          and press <Enter>.

     -    Make sure the words 'A New Product' are highlighted in 
	  the window found in the lower right hand corner of the 
	  screen; press <Enter>.

     -    Make sure the words 'Entire Product' are highlighted in 
	  the 'Choose an option' section of the screen; press <Enter>.

     -    You will be prompted to 'Insert distribution Volume 1 and 
	  press <Enter>'.   The diskette is already in the drive, 
	  therefore press <Enter>.

     -    You will see the following messages:

               Installing custom data files
               Executing Product Prep Script

     -    The message 'Creating file lists' will flash on the
          screen.  You will be prompted to 'Insert the requested 
	  Volume and press <Enter>'.  The diskette is already in 
	  the drive, therefore press <Enter>.

     -    You will see the following message:

               Extracting Files

     -    When asked if you wish to relink the kernel you should 
	  reply 'Y' in order to ensure the modifications from SLS
	  UOD370A are included in the kernel.

     -    You will then be prompted to 'Press any key to continue'; 
	  press <Enter>.

     -    At the main custom menu, move the highlighted entry to 'Quit' 
	  and press <Enter>.  Press <Enter> again on the highlighted 'Yes'.

     -    Reboot the computer.

     -    UOD370A is now successfully installed.


II.  Re-installation

Should it be necessary to re-install this SLS, you must first use custom(ADM)
to remove it.  After having successfully removed the SLS the system should 
then be shutdown and rebooted to System Maintenance mode; only then should 
custom(ADM) be used to re-install SLS UOD370A.


III. Functional Components and Description of UOD370A

Within the SCSI disk driver, scatter_rawio() performs I/O directly to user 
space.  If the I/O transfer size is set to BSIZE (1024), Sdskstart() passes 
the actual page address to Sdsk_getcmd().  If the I/O transfer size is greater
than BSIZE then Sdskstart() passes the page table address to Sdsk_getcmd().  
For transfers of size BSIZE, Sdskstart() doesn't ensure there is adequate 
space in the user area for the transfer, therefore the page following the 
user page may get corrupted.

This replacement Sdsk driver solves the problem by checking that adequate
space does exist in the user page for transfers of BSIZE, and if it does not,
Sdskstart() passes the page table address to Sdsk_getcmd() rather than the
actual page address.

The functional file installed by SLS UOD370A is:

     /etc/conf/pack.d/Sdsk/Driver.o


NOTE:  Refer to the Release and Installation Notes for more information 
       on how to use custom(ADM).


If you have any questions, please call our SCO Customer Services Department
at (408) 425-4726.  SCO Customer Service is available Monday through Friday,
6:00 A.M. to 5:00 P.M., Pacific Time.

We appreciate your business.

SCO Support Services