From owner-freebsd-hackers  Tue Mar  2  5:35:27 1999
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Date: Tue, 02 Mar 1999 13:33:41 +0000
From: Peter Edwards <peter.edwards@isocor.ie>
Organization: ISOCOR
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Subject: mmap on /dev/zero
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Hi,
I seem to remember someone a while back suggesting that you could create
shared memory between processes using mmap on /dev/zero, and passing the
open descriptor to other processes (though I might be wrong).
As a result, I thought the following might allow child and parent to
share a mapped region:

fd = open("/dev/zero", O_RDWR);
fork();
p = mmap(0, getpagesize(), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

A simple test indicated that the two mappings were seperate. (This was
on 2.2.8-RELEASE, if its of any consequence)

Is this possible to do such sharing through /dev/zero, or do I need to
inherit the mapped region? I'd like to be able to dynamically expand the
shared regions without resorting to using a normal file for the mapping,
or resorting to SysV shared mem.
(If this has been thrashed to death already, sorry, but the -hackers and
-questions archives don't appear to be searchable at the moment)

Cheers,
Peter.


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