netdev - Re: Question about an assignment in handle

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Date:	Tue, 25 May 2010 08:03:44 -0400
From:	jamal <hadi@...erus.ca>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Jiri Pirko <jpirko@...hat.com>, netdev@...r.kernel.org,
	davem@...emloft.net, kaber@...sh.net
Subject: Re: Question about an assignment in handle_ing()

On Tue, 2010-05-25 at 20:26 +1000, Herbert Xu wrote:

> In that case you should be checking whether the skb is cloned.

That is the general rule used (and what i specify to do in the docs)..
but i recall there were issues if the packet path emanated from ingress
and included multiple netdevices (earlier ex with mirror applies). There
may have been bugs then, eg I could not assume that it i had any ptype
at all that the ptype will clone the packet. Does tcpdump guarantee
skb->clone being set? I will try to test some scenarios when i am back
+settled. 

> After all, tcpdump might have simply filtered the packet out.

True - but i think thats an acceptable compromise.

> BTW, this is the case whenever you run a DHCP client/server.  So
> on most boxes your optimisation will never kick in as is.  

"Most" for people running serious firewalls or routers is not to run
DHCP servers;-> They may client, but thats a short-lived session.

> Also
> the skb may still be cloned even if there is no AF_PACKET listener.
> In that case your optimisation may be incorrect.

Did you mean that as long as there are other ptypes - which may or 
not be doing af packet? 

cheers,
jamal

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