netdev - Re: IPv6 over firewire

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Date:	Sat, 12 Jan 2013 09:27:30 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	stephan.gatzka@...il.com
Cc:	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>,
	linux1394-devel@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: IPv6 over firewire

On Jan 12 Stephan Gatzka wrote:
> 
> > And, last but big issue is, well, packet inspection at
> > driver level.  For example, you use ndisc_parse_options()
> > and code depends on CONFIG_IPV6=y.
> 
> Good point. Of course I can make firewire-net dependent from IPv6.
> 
> The other option is to build a separate firewire_ipv6 module. 
> Implementing that looks easy enough. From the original firewire net 
> driver I just need a hook to register a function that investigates 
> incoming packets for IPv6 link layer option. In addition, 
> fwnet_peer_find_by_guid must be exported.
> 
> Stefan, what is your opinion on that?

>From your previous patch it looks like that the RFC 3146 related parts in
drivers/firewire/net.c are just a few places that can be enclosed into
#if/#endif blocks.  That way, firewire-net will be built according to the
same Kconfig switches as before, and gets RFC 3146 capability if
CONFIG_IPV6=y or =m.

#if/#endif are generally not very nice, but in this case I think they can
be kept localized and thus are more beneficial than hurtful.

There is a catch:  Since both net/ipv6/Kconfig::IPV6 and
drivers/firewire/Kconfig::FIREWIRE_NET are tristate variables, we need to
prevent CONFIG_FIREWIRE_NET=y while CONFIG_IPV6=m.  One way to do that
would be like it was done for the infrared remote control support in the
firedtv driver which depends on the CONFIG_INPUT tristate variable.  This
was solved like this:
  - The helper variable drivers/media/firewire/Kconfig::DVB_FIREDTV_INPUT
    was added.
  - This variable is true if CONFIG_INPUT=y,
    or if CONFIG_DVB_FIREDTV=m and CONFIG_INPUT=m.
    In other words, if CONFIG_INPUT=m and CONFIG_DVB_FIREDTV=y, firedtv
    silently loses support for remote control input.
  - The respective firedtv parts are of course made dependent on
    CONFIG_DVB_FIREDTV.  In this case, only
    drivers/media/firewire/firedtv.h and drivers/media/firewire/Makefile
    are minimally affected.

So, if implemented like that, the special case of CONFIG_FIREWIRE_NET=y &&
CONFIG_IPV6=m would mean that firewire-net would be built but would lack
RFC 3146 support.

With a little bit more Kconfig related effort one could solve it such that
CONFIG_FIREWIRE_NET=y && CONFIG_IPV6=m would actually put RFC 3146 support
into firewire-net but would force it to be built modular instead of
statically.

Not sure which way is preferrable.  Cc'ing netdev.

In case of CONFIG_IPV6=n however, people should still be able to build
firewire-net with its current RFC 2734-only feature set.
-- 
Stefan Richter
-=====-===-= ---= -==--
http://arcgraph.de/sr/
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