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Using SECSTOPIO for printer locking

SCO's SECSTOPIO kernel parameter controlled the behavior of the stopio(S) system call. This took a file path as an argument and, if set, would cause read, write and ioctl to fail - and also send a sighup to the process that dared touch its now protected file.

The SECSTOPIO parameter turns stopio on and off (0 or 1). Apparently some versions of SCO would send two SIGHUPS in quick succession and (because processes need some time to reset their traps) this would kill the offending process.

This post concerns a printer port, but stopio can be seen in places as unexpected as telnet - see telnetd stopio.

From: Bob Bailin <72027.3605@CompuServe.COM>
Subject: Re: Open Server 5.0.5 spooler vs hot printer
References: <19990610131023.09800.00000104@ng-fk1.aol.com> 
Message-ID: <uq44D22s#GA.332@nih2naac.compuserve.com> 
Newsgroups: comp.unix.sco.misc
Date: Thu, 10 Jun 1999 14:17:34 -0400

Configure the kernel parameter SECSTOPIO = 0 to disable this feature.

dbush3054@aol.com (Dbush3054) writes:
> 
> Running Open Server 5.0.5.  Have always used the same
> physical printer as a spooler AND a hot printer (direct
> access from application). Our application creates a lock
> file in /tmp similar to this: /tmp/lp.lck to indicate
> that the printer is being used and blocks other users
> from accessing the printer until the lock file is remove
> by the application. In the past we have successfully
> modified the 'lp' script to check for the existence of
> this file and wait if necessary. The script I modified
> is in /usr/spool/lp/admins/lp/interfaces (linked to
> /var/spool/lp/admins/lp/interfaces). The 'lp' script
> was created when we created the spool printer 'lp' from
> /usr/spool/lp/model/standard).


> Does not work in Open Server 5.0.5.  After putting several
> echo statements in  the script, I have determined that
> the script file is properly waiting if the  /tmp/lp.lck
> file exists. I can watch it loop endlessly until the
> lock file is  removed by the application.  This works
> when testing because while testing I  was not actually
> printing from my application, I was just selecting the
> printer  to create the lock file and then the application
> is waiting for operator input  (the application hasn't
> actually sent anything to the printer after creating
> the lock file). When I exit the application, it removes
> the lock file and the  spooler then begins to print.
> All is well, right ?  WRONG !!!
> 
> If the application attempts to print after the spooler
> script is 'looping', the  application IMMEDIATELY gets
> logged off, which removes the lock file in /tmp  and
> allows the spooled job to print.  I think something before
> the spooler  script is closing the port, which causes my
> application to be logged when it  attempts to print.
> 
> Any suggestions ???
> 
> Thanks in Advance - Dan

-- 
Bob Bailin
72027.3605@compuserve.com

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