Path: utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!mailrus!cornell!uw-beaver!uw-june!ka
From: ka@june.cs.washington.edu (Kenneth Almquist)
Newsgroups: comp.unix.wizards
Subject: Re: SysV IPC:  eyesore or misunderstood art?
Message-ID: <8015@june.cs.washington.edu>
Date: 27 Apr 89 02:40:09 GMT
References: <28901@ucbvax.BERKELEY.EDU> <837@mtxinu.UUCP>
Organization: U of Washington, Computer Science, Seattle
Lines: 18

The shared memory the PDP-11 version of System V does actually use file
names to refer to segments.  On the other hand, if you want to change
the size of a segment, or add a new segment, you have to rebuild the
kernel.  As Ed noted, the System V IPC was not designed as a general
purpose mechanism.

I might add that a goal of the original design was to avoid penalizing
users who just wanted to do normal UNIX stuff.  All the IPC system
calls are (or at least were) optional, so that you didn't have to link
them into the kernel if you just wanted to run a vanilla UNIX time
sharing system.  This is certainly one reason for not having the IPC
code touch the file system.  (The PDP-11 shared memory was implemented
as a pseudo-device.)

The decision to include IPC in the SVID (assuming it's there; someone
correct me if I'm wrong) really contradicts the original view of the
purpose of the System V IPC.
				Kenneth Almquist