Arenas

[DanKarron at UCBVAX.BERKELEY.EDU]

>From: david pratt <lll-winken.llnl.gov!taurus!mira!pratt>
>Organization: Naval Postgraduate School, Monterey CA
>Subject: Arenas
>Greetings,
>   Thanks to everyone who answered my posting about VAX -> SGI format
> conversions. I have two more questions on a new topic, arenas.
I trust my info to you was correct.
>   1. It seems that only eight processes can access an arena. I have run
>several test and have not been able to get the ninth process to connect. Is 
>there a way around this?
     
Look at the man page for usconfig() 

     CONF_INITUSERS  Sets the maximum number of users for a given group of
                     semaphores and locks to the value given by arg0.  The
                     maximum allowable is 512 users, and the default is 8.
                     This only has effect if called before usinit(3P).  Each
                     process that calls usinit(3P) is considered a user, as is
                     each process that uses a spinlock.  It returns the
                     previously set value.

Also declare and initalize the _utrace extern var so you can see debugging
info about your arena. Note also that you need to use the multiply threaded
c library, -lmpc instead of the default -lc or -lc_s libraries. Again look
at the man page.

>   2. I want to create an arena that two different users can access. Once again
>I get a no go (Permission denied). I have tried changing the protection on 
>the file and that doesn't work. Any ideas? I know this can create a security
>problem for some applications.

I have not tried exchanging data between two different uid/gid's. This
clearly should be allowed, and controlled by the file directory bits.


>-- 
>Dave Pratt                  pratt at cs.nps.navy.mil              (408) 646-2865
>Department of Computer Science, Naval Postgraduate School, Monterey, CA 93940
>If the meek shall inherit the earth, I'm SOL!
>These are my opinions, who knows what the Navy thinks.
>

Cheers!

dan.
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