tcp: Add TCP_INFO counter for packets received out-of-order

For receive-heavy cases on the server-side, we want to track the
connection quality for individual client IPs. This counter, similar to
the existing system-wide TCPOFOQueue counter in /proc/net/netstat,
tracks out-of-order packet reception. By providing this counter in
TCP_INFO, it will allow understanding to what degree receive-heavy
sockets are experiencing out-of-order delivery and packet drops
indicating congestion.

Please note that this is similar to the counter in NetBSD TCP_INFO, and
has the same name.

Also note that we avoid increasing the size of the tcp_sock struct by
taking advantage of a hole.

Signed-off-by: Thomas Higdon <tph@fb.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index f3a85a7fb4b1..99617e528ea2 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -354,6 +354,8 @@ struct tcp_sock {
 #define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) 0
 #endif
 
+	u32 rcv_ooopack; /* Received out-of-order packets, for tcpinfo */
+
 /* Receiver side RTT estimation */
 	u32 rcv_rtt_last_tsecr;
 	struct {