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Date: Tue, 12 Dec 2000 05:00:10 -0800
From: Julian Elischer <julian@elischer.org>
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To: Alfred Perlstein <bright@wintelcom.net>
Cc: net@freebsd.org, bmilekic@freebsd.org
Subject: Re: need mbuf generic free() hook
References: <20001212042447.E16205@fw.wintelcom.net>
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Alfred Perlstein wrote:
> 
> Ok, so I'm trying to rid FreeBSD of the unp_gc() junk in uipc_usrreq.c
> I just realized why I'm leaking file descriptors:
> 
> Only mbufs with external storage can have a 'free' function, the
> problem is that for the most part when passing a single fd I'm only
> using a single mbuf to pass my data around, my ext_free routine is
> probably never called, and on top of that I'm probably corrupting
> my mbuf by using it when I shouldn't be.
> 
> This is terrible, what should be a simple free() hook is now my
> worst nightmare.  A couple of options come to mind:
> 
> a) always have a free hook, the extra if (m->m_freehook != NULL)
> check can't be that expensive.
> b) a macro to make an mbuf into an mbuf cluster that points to itself,
> it should check to see if it has enough room to shuffle the data
> and return an error if it can't accomidate both the data and the
> expanded mbug header.
> 
> I like 'a' but would be willing to deal with 'b' as we've never
> had a need for this, although that would mean copying about the
> size of an mbuf in the worst case when a subsystem needs this
> facility.


The external object in the mbuf can be virtual.
You can Say it is external and point the pointers to a static place
and set the mbuf to b ereadonly and have an m_len of 0
Then your free routine woild be called, but you would not
need to alocate a cluster for it.
> 
> Suggestions? Comments?
> 
> --
> -Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
> "I have the heart of a child; I keep it in a jar on my desk."
> 
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-- 
      __--_|\  Julian Elischer
     /       \ julian@elischer.org
    (   OZ    ) World tour 2000
---> X_.---._/  presently in:  Budapest
            v





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