netdev - Re: [PATCH] TX_RING and packet mmap

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Date:	Tue, 07 Apr 2009 08:48:40 -0400
From:	jamal <hadi@...erus.ca>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Johann Baudy <johann.baudy@...-log.net>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH] TX_RING and packet mmap

On Tue, 2009-04-07 at 15:26 +0800, Herbert Xu wrote:

> What if something modifies skb->mark after it's sent? 
> For now the only thing I can think of is a tc netfilter action.  So you could
> also solve the problem by removing that feature since IMHO it is
> pretty dodgy :)

I see it as being non-trivial even with tc/mark. What did you
have in mind? 
If it was possible to have a different skb->cookie (other than
skb->mark, sort of "global cb") which the sender sets and 
the kernel never touches then this would be easy. The skb->destructor
can then be sure that it was the original skb in the lookup. Such a
field could serve other purposes like notify user space that the packet
has been really sent out (eg in the case of tun). But that would require
a new field on the skb.

[For a fleeting latte-moment there i thought i had a clever idea: I
wanted to say that the numeric (32/64 bit) allocated address of the skb
may be useful for the cookie but i think that could change in the skb's
kernel lifetime (skb_expand etc).]

cheers,
jamal

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