Date: Tue, 10 Oct 2000 23:21:49 -0400 (EDT) From: Bosko Milekic <bmilekic@dsuper.net> To: Archie Cobbs <archie@whistle.com> Cc: freebsd-net@freebsd.org Subject: Re: ip_input.c patch Message-ID: <Pine.BSF.4.21.0010102314260.9539-100000@jehovah.technokratis.com> In-Reply-To: <200010110114.e9B1E0J40614@bubba.whistle.com>
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On Tue, 10 Oct 2000, Archie Cobbs wrote:
> I think I'll wait for your diffs.
>
> Uh oh.. I just thought of a plan.. :-)
>
>
> 1. Add a new macro to make an mbuf writable:
>
> #define M_MKWRITABLE(m, len)
> do {
> if ((m)->m_len < (len)
> || (((m)->m_flags & M_EXT) != 0 && MEXT_IS_REF(m))) {
> (m) = m_pullup((m), (len));
> }
> } while (0)
This is very similar to what I already have in these diffs (I'll post
the old version tomorrow after my exam so that you can beat it up as you
like :-) ). The difference is that in the diffs we already have, there is
an additional flag added to the mbuf... for various different reasons
(this is all archived probably in -net mail archives...) ... It would be
cool to revive this this weekend and commit it. I'll do it by upcoming
Sunday, because I know also that dwmalone was planning to commit some
related stuff following that. I'll keep you and -net posted.
> 2. Temporarily change the definition of mtod() as follows:
>
> BEFORE
> ------
>
> #define mtod(m, t) ((t)((m)->m_data))
>
> AFTER
> -----
>
> #define mtod(m, t) ((const t)((m)->m_data))
>
> 3. Compile LINT and find and fix every place that generates
> an error from the const-cast in mtod():
>
> (A) If the code doesn't need to modify the mbuf (probably
> 99% of the time), then change it like so:
>
> BEFORE
> ------
> struct ip *ip;
> ip = mtod(m, struct ip *);
>
> AFTER
> ------
> const struct ip *ip;
> ip = mtod(m, struct ip *);
>
> (B) If the code does modify the mbuf, insert M_MKWRITABLE()
> at the appropriate point.
>
> 4. Put mtod() back the way it was
>
> -Archie
That's a pretty clever way of catching potentially problematic
areas... let me finish this one last test tomorrow and I'll post another
followup with more information regarding this diff I keep talking about
(which I'll fish out of the attic then). :-)
> ___________________________________________________________________________
> Archie Cobbs * Whistle Communications, Inc. * http://www.whistle.com
Cheers,
Bosko Milekic
bmilekic@technokratis.com
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