[bpf-next 2/2] bpf: add BPF_SOCK_OPS_STATS_CB for tcp_stats()

[Yafang Shao <laoar.shao@gmail.com>]

Introuce this new op BPF_SOCK_OPS_STATS_CB for tcp_stats() such that it
can be traced via BPF on a per socket basis.
There's one argument in BPF_SOCK_OPS_STATS_CB, which is Linux MIB index
LINUX_MIB_* to indicate the TCP event.
All these Linux MIBs are defined in include/uapi/linux/snmp.h.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 include/uapi/linux/bpf.h | 5 +++++
 net/ipv4/tcp_input.c     | 1 +
 2 files changed, 6 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1777fa0..0314ddd 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2894,6 +2894,11 @@ enum {
 	BPF_SOCK_OPS_TCP_LISTEN_CB,	/* Called on listen(2), right after
 					 * socket transition to LISTEN state.
 					 */
+	BPF_SOCK_OPS_STATS_CB,		/*
+					 * Called on tcp_stats().
+					 * Arg1: Linux MIB index
+					 * 	 LINUX_MIB_*
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 88deb1f..4acf458 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3557,6 +3557,7 @@ static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
 static void tcp_stats(struct sock *sk, int mib_idx)
 {
 	NET_INC_STATS(sock_net(sk), mib_idx);
+	tcp_call_bpf(sk, BPF_SOCK_OPS_STATS_CB, 1, &mib_idx);
 }
 
 /* This routine deals with incoming acks, but not outgoing ones. */
-- 
1.8.3.1