Path: utzoo!utgpu!cunews!bnrgate!brtph3!brchh104!brchs1!bnr.ca!rice.edu!sun-spots-request
From: klemets@sics.se (Anders Klemets)
Newsgroups: comp.sys.sun
Subject: Problem with shared memory on SunOS 4.1
Keywords: SunOS
Message-ID: <568@brchh104.bnr.ca>
Date: 30 Nov 90 21:16:17 GMT
Sender: news@brchh104.bnr.ca
Organization: Sun-Spots
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Approved: Sun-Spots@rice.edu
X-Original-Date: Fri, 23 Nov 90 18:30:21 GMT
X-Sun-Spots-Digest: Volume 9, Issue 384, message 8
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I have a client/server application that uses shared memory. The shared
memory segment must be mapped onto the same address by all participating
processes. A client attaches the shared memory segment with

	id = shmget(key, 0, 0);
	addr = shmat(id, 0, 0);

This will make the kernel choose on which address to put the shared memory
segment. This usually turns out to be the "right" address. But if not, I
detach the segment and attach it at the right address with

	shmdt(addr);
	addr = shmat(id, rightaddr, 0);

At this point the call to shmat() always fails on a Sun-4 with SunOS 4.1
It returns with errno: "invalid argument." I have never experienced that
this code would fail on SunOS 4.0.3 or on System V release 3.2. 

What could be wrong? It seems unlikely that the memory pointed at by
"rightaddr" would be in use by some other part of the process.

Anders Klemets			klemets@sics.se