David S. Miller wrote:

>On Sun, 02 Jan 2005 22:19:45 +0100
>Patrick McHardy <kaber@trash.net> wrote:
>
>  
>
>>skb_ip_make_writable copies the packet as soon as the data area needs
>>to be touched. This is of course necessary for packets generated locally,
>>but can't we mangle the data area of skbs with skb->sk == NULL without
>>copying them ?
>>    
>>
>
>Not if they are cloned.  tcpdump can still share access to the
>packet.
>
>  
>
I wasn't very clear in my question, it only makes sense if you look at
skb_ip_make_writable :) It already checks for skb_shared || skb_cloned
to decide when to copy, but additionally makes some guesses based on the
protocol. I think the checks for skb_shared || skb_clones should already
catch all cases where copying is necessary, and the additional cases
could be removed.

Regards
Patrick