netdev - Re: SKB Reference Question

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Date:   Wed, 01 Nov 2017 10:33:31 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Joe Smith <codesoldier1@...il.com>
Cc:     netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: SKB Reference Question

On Wed, 2017-11-01 at 10:27 -0700, Joe Smith wrote:
> How strictly are references on the SKB enforced. For example,
> tcp_transmit_skb() clones the SKB and adds a TCP header. Can I assume
> that in case of re-transmission the header added will be there and can
> be reused instead of creating a new one from scratch. Some fields like
> time stamp would need to be updated but they should be unmodified.


Not sure what you are trying to do, but this seems messy ;)

At rtx time, there is no guarantee that the master skb has not been
changed, so the content of TCP header might be wrong anyway.