netdev - Re: [PATCH 1/1] 6lowpan: Fix fragmentation with link-local compressed addresses

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Date:	Mon, 20 May 2013 08:50:58 +0200
From:	Alexander Aring <alex.aring@...il.com>
To:	David Hauweele <david@...weele.net>
Cc:	Alexander Smirnov <alex.bluesman.smirnov@...il.com>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-zigbee-devel@...ts.sourceforge.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] 6lowpan: Fix fragmentation with link-local
 compressed addresses

Hi David,

I will try to figure out why link-layer address doesn't work on my
setup.

On Mon, May 20, 2013 at 12:14:48AM +0200, David Hauweele wrote:
> Hello,
> 
> There is a patch which fixes link-local address uncompression:
> 
> http://permalink.gmane.org/gmane.linux.network.zigbee.devel/1717
> 
> I came across a similar solution but didn't submit it as another patch
> already existed.
> This patch instead focus on fragmented packet with link-local address
> compression,
> which is related but a different bug.
> 
> 2013/5/19 Alexander Aring <alex.aring@...il.com>:
> > Hi David,
> >
> > can you use a link-layer address on the current net-next kernel?
> >
> > I am asking because I can't use a link-layer address currently.
> > Your patch doesn't help to solve my problem with link-layer addresses.
> >
> >
> > To your patch:
> >
> > We get the link-layer addresses from skb not from the allocated
> > frame->skb.
> >
> > Here is the code:
> >
> > _saddr = mac_cb(skb)->sa.hwaddr;
> > _daddr = mac_cb(skb)->da.hwaddr;
> >
> > Here is skb != frame->skb so we don't need to copy it to frame->skb->cb
> > because we already the link-layer addresses from skb->cb.
> >
> > Is there another place in the code where we get the link-layer addresses
> > from allocated "frame" structure?
> 
> frame->skb is used to reassemble the 6lowpan packet when new fragments
> are received.
> This is the 'fragments assembling' switch at the beginning of
> lowpan_process_data().
> It will reassemble fragments until the packet is successfully reassembled.
> Once it is, skb is replaced:
> 
> dev_kfree_skb(skb);
> skb = frame->skb;
> kfree(frame);
> 

ah ok.
> And the process continues as with other 6lowpan packets.
> 
> In particular:
> 
> _saddr = mac_cb(skb)->sa.hwaddr;
> _daddr = mac_cb(skb)->da.hwaddr;
> 
> Several lines later there are:
> 
> err = lowpan_uncompress_addr(skb, &hdr.saddr, lowpan_llprefix,
> lowpan_unc_llconf[tmp], skb->data);
> err = lowpan_uncompress_addr(skb, &hdr.daddr, lowpan_llprefix,
> lowpan_unc_llconf[tmp], skb->data);

I think you mean uncompress and compress here.

> 
> These two lines should use _saddr/_daddr instead of skb->data, which
I agree with that.

Regards
Alex
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