Re: [PATCH 7/8] fwd: Update all port maps before applying exclusions

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Oct 30, 2025 at 09:24:07PM +0100, Stefano Brivio wrote:
> On Sat, 11 Oct 2025 15:48:26 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > In fwd_scan_ports() we go through each of the automatic forwarding cases
> > (tcp, udp, inbound and outbound) in turn, scanning and calculating the
> > new forwarding map.  However, to avoid avoid circular forwarding, some of
> > these maps affect each other.  This has the odd effect that the ones
> > handled earlier are based on the previous scan of other maps, whereas
> > the later ones are based on the latest scan.
> > 
> > That's not generally harmful, but it is counter-intuitive and results in a
> > few odd edge cases.  Avoid this by performing all the scans first, without
> > regard to other maps, then applying the exclusions afterwards.
> > 
> > One case has an extra wrinkle: for UDP we forwarded not just ports that
> > were listening on UDP but ones listening on TCP as well, for the benefit of
> > protocols like iperf3.  We therefore also excluded listening ports from
> > both UDP and TCP from the other direction to avoid circular forwarding.
> > 
> > This doesn't really make sense, though.  To avoid circular forwarding, we
> > don't care *why* the other side is listening on UDP, just that it *is*
> > listening.  I believe the explicit handling of the reverse TCP map was only
> > needed because the reverse map might have been one cycle out of date and
> > therefore not included a port opened because of the corresponding TCP port.
> 
> Right, yes, that was the reason. I guess it makes sense to make this
> less hypothetical in the commit message if you re-spin. Same in 8/8.

There are some (trivial) conflicts with other things you've merged, so
I will respin.  I've fixed this up.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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