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Re: pskb change in dst->output

To: James Morris <jmorris@xxxxxxxxxx>
Subject: Re: pskb change in dst->output
From: "David S. Miller" <davem@xxxxxxxxxx>
Date: Fri, 9 Jul 2004 12:36:08 -0700
Cc: herbert@xxxxxxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <Xine.LNX.4.44.0407091001460.3887-100000@thoron.boston.redhat.com>
References: <20040709081443.GA11101@gondor.apana.org.au> <Xine.LNX.4.44.0407091001460.3887-100000@thoron.boston.redhat.com>
Sender: netdev-bounce@xxxxxxxxxxx
On Fri, 9 Jul 2004 10:02:25 -0400 (EDT)
James Morris <jmorris@xxxxxxxxxx> wrote:

> On Fri, 9 Jul 2004, Herbert Xu wrote:
> 
> > On Thu, Jul 08, 2004 at 02:02:35PM +1000, herbert wrote:
> > > 
> > > That's only because the dst->output() functions are calling
> > > skb_checksum_help().  Since those same functions assume the
> > > skb to be "uncloned" anyway (they modify it directly by adding
> > > headers etc.), they only need to call a version of
> > > skb_checksum_help() that does not do a copy of the skb.
> > 
> > If there are no objections, I'd like to create a version of
> > skb_checksum_help() that doesn't copy the packet, and call
> > that version from ah_output()/esp_output()/ipcomp_output().
> 
> This will break when cloned packets are passed to these functions.

James is right Herbert.  TCP will send clones down into these routines
all the time.

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