netdev - [PATCH net-next] net/packet: add PACKET_FANOUT_FLAG_IGNORE

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Date:   Thu, 27 Oct 2022 17:10:14 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
        pabeni@...hat.com, vincent.whitchurch@...s.com, cpascoe@...gle.com,
        Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net-next] net/packet: add PACKET_FANOUT_FLAG_IGNORE_OUTGOING

From: Willem de Bruijn <willemb@...gle.com>

Extend packet socket option PACKET_IGNORE_OUTGOING to fanout groups.

The socket option sets ptype.ignore_outgoing, which makes
dev_queue_xmit_nit skip the socket.

When the socket joins a fanout group, the option is not reflected in
the struct ptype of the group. dev_queue_xmit_nit only tests the
fanout ptype, so the flag is ignored once a socket joins a
fanout group.

Inheriting the option from a socket would change established behavior.
Different sockets in the group can set different flags, and can also
change them at runtime.

Testing in packet_rcv_fanout defeats the purpose of the original
patch, which is to avoid skb_clone in dev_queue_xmit_nit (esp. for
MSG_ZEROCOPY packets).

Instead, introduce a new fanout group flag with the same behavior.

Tested with https://github.com/wdebruij/kerneltools/blob/master/tests/test_psock_fanout_ignore_outgoing.c

Signed-off-by: Willem de Bruijn <willemb@...gle.com>
---
 include/uapi/linux/if_packet.h | 1 +
 net/packet/af_packet.c         | 1 +
 2 files changed, 2 insertions(+)

diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h
index c07caf7b40db6..a8516b3594a44 100644
--- a/include/uapi/linux/if_packet.h
+++ b/include/uapi/linux/if_packet.h
@@ -70,6 +70,7 @@ struct sockaddr_ll {
 #define PACKET_FANOUT_EBPF		7
 #define PACKET_FANOUT_FLAG_ROLLOVER	0x1000
 #define PACKET_FANOUT_FLAG_UNIQUEID	0x2000
+#define PACKET_FANOUT_FLAG_IGNORE_OUTGOING     0x4000
 #define PACKET_FANOUT_FLAG_DEFRAG	0x8000
 
 struct tpacket_stats {
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 8c5b3da0c29f6..44f20cf8a0c0e 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1777,6 +1777,7 @@ static int fanout_add(struct sock *sk, struct fanout_args *args)
 		match->prot_hook.af_packet_net = read_pnet(&match->net);
 		match->prot_hook.id_match = match_fanout_group;
 		match->max_num_members = args->max_num_members;
+		match->prot_hook.ignore_outgoing = type_flags & PACKET_FANOUT_FLAG_IGNORE_OUTGOING;
 		list_add(&match->list, &fanout_list);
 	}
 	err = -EINVAL;
-- 
2.38.1.273.g43a17bfeac-goog