packet: add sockopt to ignore outgoing packets
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@axis.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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