netdev - Re: IPv6 over Firewire

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Date:	Sat, 22 Dec 2012 04:49:03 +0900
From:	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
To:	stephan.gatzka@...il.com
CC:	netdev@...r.kernel.org, linux1394-devel@...ts.sourceforge.net,
	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
Subject: Re: IPv6 over Firewire

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));
+       }
 }

--yoshfuji
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