netdev - Re: [PATCH v2 net-next] packet: add sockopt to ignore outgoing packets

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Date:   Wed, 05 Sep 2018 22:10:28 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     vincent.whitchurch@...s.com
Cc:     netdev@...r.kernel.org, willemb@...gle.com, rabinv@...s.com
Subject: Re: [PATCH v2 net-next] packet: add sockopt to ignore outgoing
 packets

From: Vincent Whitchurch <vincent.whitchurch@...s.com>
Date: Mon,  3 Sep 2018 16:23:36 +0200

> Currently, the only way to ignore outgoing packets on a packet socket is
> via the BPF filter.  With MSG_ZEROCOPY, packets that are looped into
> AF_PACKET are copied in dev_queue_xmit_nit(), and this copy happens even
> if the filter run from packet_rcv() would reject them.  So the presence
> of a packet socket on the interface takes away the benefits of
> MSG_ZEROCOPY, even if the packet socket is not interested in outgoing
> packets.  (Even when MSG_ZEROCOPY is not used, the skb is unnecessarily
> cloned, but the cost for that is much lower.)
> 
> Add a socket option to allow AF_PACKET sockets to ignore outgoing
> packets to solve this.  Note that the *BSDs already have something
> similar: BIOCSSEESENT/BIOCSDIRECTION and BIOCSDIRFILT.
> 
> The first intended user is lldpd.
> 
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
> ---
> v2: Stricter value validation.
>     Moved ignore check out of skb_loop_sk().

Applied, thank you.