selftests/bpf: Add Userspace tests for TCP_WINDOW_CLAMP

Adding selftests for new added functionality to set TCP_WINDOW_CLAMP
from bpf setsockopt.
Signed-off-by: Prankur gupta <prankgup@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201202213152.435886-3-prankgup@fb.com

tools/testing/selftests/bpf/bpf_tcp_helpers.h

@@ -56,6 +56,7 @@ struct tcp_sock {
 	__u32	rcv_nxt;
 	__u32	snd_nxt;
 	__u32	snd_una;
+	__u32	window_clamp;
 	__u8	ecn_flags;
 	__u32	delivered;
 	__u32	delivered_ce;

tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c

@@ -42,6 +42,10 @@ static void verify_result(struct tcpbpf_globals *result)
 
 	/* check getsockopt for SAVED_SYN */
 	ASSERT_EQ(result->tcp_saved_syn, 1, "tcp_saved_syn");
+
+	/* check getsockopt for window_clamp */
+	ASSERT_EQ(result->window_clamp_client, 9216, "window_clamp_client");
+	ASSERT_EQ(result->window_clamp_server, 9216, "window_clamp_server");
 }
 
 static void run_test(struct tcpbpf_globals *result)

tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c

@@ -12,17 +12,41 @@
 #include <linux/tcp.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
+#include "bpf_tcp_helpers.h"
 #include "test_tcpbpf.h"
 
 struct tcpbpf_globals global = {};
 int _version SEC("version") = 1;
 
+/**
+ * SOL_TCP is defined in <netinet/tcp.h> while
+ * TCP_SAVED_SYN is defined in already included <linux/tcp.h>
+ */
+#ifndef SOL_TCP
+#define SOL_TCP 6
+#endif
+
+static __always_inline int get_tp_window_clamp(struct bpf_sock_ops *skops)
+{
+	struct bpf_sock *sk;
+	struct tcp_sock *tp;
+
+	sk = skops->sk;
+	if (!sk)
+		return -1;
+	tp = bpf_skc_to_tcp_sock(sk);
+	if (!tp)
+		return -1;
+	return tp->window_clamp;
+}
+
 SEC("sockops")
 int bpf_testcb(struct bpf_sock_ops *skops)
 {
 	char header[sizeof(struct ipv6hdr) + sizeof(struct tcphdr)];
 	struct bpf_sock_ops *reuse = skops;
 	struct tcphdr *thdr;
+	int window_clamp = 9216;
 	int good_call_rv = 0;
 	int bad_call_rv = 0;
 	int save_syn = 1;
@@ -75,6 +99,11 @@ int bpf_testcb(struct bpf_sock_ops *skops)
 	global.event_map |= (1 << op);
 
 	switch (op) {
+	case BPF_SOCK_OPS_TCP_CONNECT_CB:
+		rv = bpf_setsockopt(skops, SOL_TCP, TCP_WINDOW_CLAMP,
+				    &window_clamp, sizeof(window_clamp));
+		global.window_clamp_client = get_tp_window_clamp(skops);
+		break;
 	case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
 		/* Test failure to set largest cb flag (assumes not defined) */
 		global.bad_cb_test_rv = bpf_sock_ops_cb_flags_set(skops, 0x80);
@@ -100,6 +129,10 @@ int bpf_testcb(struct bpf_sock_ops *skops)
 				global.tcp_saved_syn = v;
 			}
 		}
+		rv = bpf_setsockopt(skops, SOL_TCP, TCP_WINDOW_CLAMP,
+				    &window_clamp, sizeof(window_clamp));
+
+		global.window_clamp_server = get_tp_window_clamp(skops);
 		break;
 	case BPF_SOCK_OPS_RTO_CB:
 		break;

tools/testing/selftests/bpf/test_tcpbpf.h

@@ -16,5 +16,7 @@ struct tcpbpf_globals {
 	__u32 num_close_events;
 	__u32 tcp_save_syn;
 	__u32 tcp_saved_syn;
+	__u32 window_clamp_client;
+	__u32 window_clamp_server;
 };
 #endif