Re: [Ieee80211-devel] Re: ipw2200 - hw address problem

[Zhu Yi <yi...@in...>]

On Thu, 2005-08-04 at 14:04 -0500, James Ketrenos wrote:
> James Ketrenos wrote:
> 
> >Yi -- if you have time during your day today, can you take a look at
> >this?  We should be able to modify ieee80211_tx's ieee80211_xmit()
> >method so that it doesn't have to overwrite the incoming SKB and can
> >just stick the snap on the first TXB constructed.  If I have some more
> >free time today I'll take a crack at it and send out a patch if I get it
> >done.  If you don't see a patch from me for the above, assume I didn't
> >get to look into it further.
> >  
> >
> Alright; I had few minutes.  Try the attached (it runs here, don't know
> if it will solve the problem though)

You are right. The skb is shared between ieee80211_xmit and PF_PACKET
socket (if any). So if we change it in the stack, the raw socket will
also see the change. I think it is another good reason for the native
ieee80211 stack. If we process protocol headers in network stacks
instead of dev->hard_start_xmit, we won't have this kind of problem.
Currently I think making a copy to the skb can solve it well.

You patch is correct. Another apporach is using skb_unshare() at the
beginning of ieee80211_xmit(). It will copy another skb only if the skb
is cloned. So the overload is also small. I've attached the patch FYI.

Thanks,
-yi