From mboxrd@z Thu Jan  1 00:00:00 1970
From: "David S. Miller" <davem@davemloft.net>
Subject: Re: skb_ip_make_writable and skbs not owned by a socket
Date: Mon, 17 Jan 2005 13:50:29 -0800
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To: Patrick McHardy <kaber@trash.net>
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On Fri, 14 Jan 2005 06:59:00 +0100
Patrick McHardy <kaber@trash.net> wrote:

> 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.

This code is doing something different.  Even if we unclone and
unshare the SKB, the packet header portion can still be non-linear.

It will be possible for devices to create this situation on receive.
That's why we have all the pskb_may_pull() checks in all the major
ipv4 protocol input paths.