Date: Tue, 2 Mar 1999 09:43:09 -0500 (EST) From: Alfred Perlstein <bright@cygnus.rush.net> To: Peter Edwards <peter.edwards@isocor.ie> Cc: freebsd-hackers@FreeBSD.ORG, green@unixhelp.org Subject: Re: mmap on /dev/zero Message-ID: <Pine.BSF.3.96.990302094001.7848p-100000@cygnus.rush.net> In-Reply-To: <36DBE8B5.A612F447@isocor.ie>
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On Tue, 2 Mar 1999, Peter Edwards wrote:
> 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)
It has. :)
You can not do this, you must inherit the shared segment or use SYSV.
I do remeber someone trying some evil hack with /proc but i don't know
if they were successful... were you Brian Feldman? :)
-Alfred
>
> Cheers,
> Peter.
>
>
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