Re: Regarding dev->addr_len

[Alexander Aring <alex.aring@gmail.com>]

Hi Varka,

On Fri, Aug 08, 2014 at 02:10:48PM +0530, Varka Bhadram wrote:
> Hi Alex,
> 
> I need some clarification regarding address length for the netdevice.
> We are always setting up that to IEEE802154_ADDR_LEN [1].
> 
> If i receive a packet (RS: Router Solicitation) with short addressing mode,
> it is discarding at higher layers.
> 
> If the linux node receives the RS packet from TinyOS node its discarding
> at [2] due to address length field. Here [2] we are getting *lladdr* as NULL.
> 

yes, I said about some months ago to Martin that he should not use short
addresses in 6lowpan because it's simply not working currently.

> 
> Actually we have to update the dev->addr_len filed as per the packet info it received ..?
> 

If you look at net/ipv6/ndisc.c code you will notice that when you
change the addr_len of netdevice during runtime will end in an
unexecpted behaviour.

> How can we make it work..?
> 

I already open a thread to related this question [0]. Please don't open a
new one! David wrote something I need to answer him, but need to
consider how I can describe the current behaviour in words.

We can't just do own changes in net/ipv6/ndisc.c, only very very small
changes and changes which don't brake the ethernet, etc... neighbor
discovery. I have several ideas to deal with, some need a complete
change of architecture to deal with short and extended addresses.

Currently we have in dev_addr the extended address and the addr_len is a
static value. And that's also what the neighbor discovery use from L2,
the addr_len and dev_addr only.

Okay, there are also the header_ops callbacks, I need to take a closer
look into that to have some idea.

- Alex

[0] http://www.spinics.net/lists/netdev/msg291767.html