netdev - Re: [RFC v2] mac80211: assign needed

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Date:	Mon, 05 May 2008 22:10:14 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	David Miller <davem@...emloft.net>
Cc:	tomasw@...il.com, linville@...driver.com, netdev@...r.kernel.org,
	linux-wireless@...r.kernel.org
Subject: Re: [RFC v2] mac80211: assign needed_headroom/tailroom for netdevs


> And the copy is necessary because you need more tailroom or something?
> 
> I don't understand why simply having all the space you need is not
> better and faster :-)
> 
> Even if you have a clone, you can muck with the data in the IP and TCP
> header areas, so long as skb_header_cloned() is false.

I think it's probably all because I don't understand skb_cloned() vs.
skb_header_cloned() and mac80211 came with checks for skb_cloned() that
I didn't spot.

So you're saying the check there to see if we can add 802.11 headers
should depend on skb_header_cloned() and not skb_cloned()?

> So I can only conclude that your problematic case is that of
> encryption, right?  That's the only situation where I can imagine you
> need to modify with packet data outside of the protocol headers.

When is protocol header equivalent to skb header and when not?

johannes

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