netdev - Re: IPv6 over Firewire

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Message-ID: <20121222001230.3fe92bef@stein>
Date:	Sat, 22 Dec 2012 00:12:30 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>,
	stephan.gatzka@...il.com
Cc:	netdev@...r.kernel.org, linux1394-devel@...ts.sourceforge.net
Subject: Re: IPv6 over Firewire

On Dec 22 YOSHIFUJI Hideaki wrote:
> Stephan Gatzka wrote:
> > 
> >> If you are talking about how to build NS/NA/RS/Redirect messages, you
> >> can just use ndisc_opt_addr_space() and ndisc_fill_addr_option() here.
> > 
> > Thanks, these functions are certainly helpful. But ndisc_opt_addr_space() calculates the required space from dev->addr_len and ndisc_addr_option_pad(dev->type). The latter is 0 for IEEE1394 (firewire). So the required option space just comes from dev->addr_len, which is 8 for firewire, resulting in an option address space of 16 (2 octets).
> > 
> > But rfc3146 requires an option address space of 3 octets. So my main question is if in such a situation the best is to reserve additional skb tail room using needed_tailroom in struct netdevice. This directly affects the memory allocated in ndisc_build_skb().
> 
> Something like this:
> 
>  static inline int ndisc_opt_addr_space(struct net_device *dev)
>  {
> -       return NDISC_OPT_SPACE(dev->addr_len + ndisc_addr_option_pad(dev->type));
> +       switch (dev->type) {
> +       case ARPHRD_IEEE1394:
> +               return sizeof(struct ndisc_opt_ieee1394_llinfo);
> +       default:
> +               return NDISC_OPT_SPACE(dev->addr_len + ndisc_addr_option_pad(dev->type));
> +       }
>  }

Can't we increase dev->addr_len for RFC 3146 interfaces?
Can't we add another dev->type besides ARPHRD_IEEE1394 (RFC 2734)?

Is a single dev instance transporting both IPv4 and IPv6 or will there be
separate instances for those?
-- 
Stefan Richter
-=====-===-- ==-- =-==-
http://arcgraph.de/sr/
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