netdev - Re: [PATCH net] datagram: When peeking datagrams with offset

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Message-ID: <CAF=yD-+jBim==ktwYUNAFkn-N4eabqgNME8NXM77v9-U_bfWPg@mail.gmail.com>
Date:   Tue, 15 Aug 2017 13:00:14 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Matthew Dawson <matthew@...systems.ca>,
        Network Development <netdev@...r.kernel.org>,
        "Macieira, Thiago" <thiago.macieira@...el.com>
Subject: Re: [PATCH net] datagram: When peeking datagrams with offset < 0
 don't skip empty skbs

> There is another difference between reading sk_peek_offset in the
> caller or in __skb_try_recv_from_queue. The latter is called repeatedly
> when it returns NULL. Each call can modify *off. I believe that it needs
> to restart with _off at sk->sk_peek_off each time, as it restarts from the
> head of the queue each time.

I made a mistake here. *off is not updated when returning NULL.

In that case, it is better to read sk_peek_offset once, than to read
it each time __skb_try_recv_from_queue is entered.