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>

1 files changed, 17 insertions, 0 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 75c92a87e7b2..f85f67b5c1f4 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3805,6 +3805,20 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
 
                 return fanout_set_data(po, optval, optlen);
         }
+        case PACKET_IGNORE_OUTGOING:
+        {
+                int val;
+
+                if (optlen != sizeof(val))
+                        return -EINVAL;
+                if (copy_from_user(&val, optval, sizeof(val)))
+                        return -EFAULT;
+                if (val < 0 || val > 1)
+                        return -EINVAL;
+
+                po->prot_hook.ignore_outgoing = !!val;
+                return 0;
+        }
         case PACKET_TX_HAS_OFF:
         {
                 unsigned int val;
@@ -3928,6 +3942,9 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
                         ((u32)po->fanout->flags << 24)) :
                        0);
                 break;
+        case PACKET_IGNORE_OUTGOING:
+                val = po->prot_hook.ignore_outgoing;
+                break;
         case PACKET_ROLLOVER_STATS:
                 if (!po->rollover)
                         return -EINVAL;