Date: Tue, 2 Mar 1999 18:04:38 -0500 (EST) From: Brian Feldman <green@unixhelp.org> To: Alfred Perlstein <bright@cygnus.rush.net> Cc: Peter Edwards <peter.edwards@isocor.ie>, freebsd-hackers@FreeBSD.ORG Subject: Re: mmap on /dev/zero Message-ID: <Pine.BSF.4.05.9903021803270.8315-100000@janus.syracuse.net> In-Reply-To: <Pine.BSF.3.96.990302094001.7848p-100000@cygnus.rush.net>
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On Tue, 2 Mar 1999, Alfred Perlstein wrote:
>
>
> 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? :)
Me? I was just mmaping in parts of /proc/foopid/mem =)
>
> -Alfred
>
>
> >
> > Cheers,
> > Peter.
> >
> >
> > To Unsubscribe: send mail to majordomo@FreeBSD.org
> > with "unsubscribe freebsd-hackers" in the body of the message
> >
>
>
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