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packet: add sockopt to ignore outgoing packets

Browse source 
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 <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Vincent Whitchurch 2018-09-03 16:23:36 +02:00 • committed by David S. Miller
commit fa788d986a
4 changed files with 22 additions and 0 deletions
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17
net/packet/af_packet.c
View file

@ -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;