bpf: tcp: Add bpf_cubic example

This patch adds a bpf_cubic example.  Some highlights:
1. CONFIG_HZ .kconfig map is used.
2. In bictcp_update(), calculation is changed to use usec
   resolution (i.e. USEC_PER_JIFFY) instead of using jiffies.
   Thus, usecs_to_jiffies() is not used in the bpf_cubic.c.
3. In bitctcp_update() [under tcp_friendliness], the original
   "while (ca->ack_cnt > delta)" loop is changed to the equivalent
   "ca->ack_cnt / delta" operation.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200122233658.903774-1-kafai@fb.com

tools/testing/selftests/bpf/bpf_tcp_helpers.h

@@ -6,13 +6,28 @@
 #include <linux/types.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_core_read.h>
+#include "bpf_trace_helpers.h"
+
+#define BPF_STRUCT_OPS(name, args...) \
+SEC("struct_ops/"#name) \
+BPF_PROG(name, args)
+
+#define tcp_jiffies32 ((__u32)bpf_jiffies64())
 
 struct sock_common {
 	unsigned char	skc_state;
 } __attribute__((preserve_access_index));
 
+enum sk_pacing {
+	SK_PACING_NONE		= 0,
+	SK_PACING_NEEDED	= 1,
+	SK_PACING_FQ		= 2,
+};
+
 struct sock {
 	struct sock_common	__sk_common;
+	unsigned long		sk_pacing_rate;
+	__u32			sk_pacing_status; /* see enum sk_pacing */
 } __attribute__((preserve_access_index));
 
 struct inet_sock {
@@ -54,6 +69,7 @@ struct tcp_sock {
 	__u32	max_packets_out;
 	__u32	lsndtime;
 	__u32	prior_cwnd;
+	__u64	tcp_mstamp;	/* most recent packet received/sent */
 } __attribute__((preserve_access_index));
 
 static __always_inline struct inet_connection_sock *inet_csk(const struct sock *sk)

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

@@ -4,6 +4,7 @@
 #include <linux/err.h>
 #include <test_progs.h>
 #include "bpf_dctcp.skel.h"
+#include "bpf_cubic.skel.h"
 
 #define min(a, b) ((a) < (b) ? (a) : (b))
 
@@ -158,6 +159,28 @@ static void do_test(const char *tcp_ca)
 	close(fd);
 }
 
+static void test_cubic(void)
+{
+	struct bpf_cubic *cubic_skel;
+	struct bpf_link *link;
+
+	cubic_skel = bpf_cubic__open_and_load();
+	if (CHECK(!cubic_skel, "bpf_cubic__open_and_load", "failed\n"))
+		return;
+
+	link = bpf_map__attach_struct_ops(cubic_skel->maps.cubic);
+	if (CHECK(IS_ERR(link), "bpf_map__attach_struct_ops", "err:%ld\n",
+		  PTR_ERR(link))) {
+		bpf_cubic__destroy(cubic_skel);
+		return;
+	}
+
+	do_test("bpf_cubic");
+
+	bpf_link__destroy(link);
+	bpf_cubic__destroy(cubic_skel);
+}
+
 static void test_dctcp(void)
 {
 	struct bpf_dctcp *dctcp_skel;
@@ -184,4 +207,6 @@ void test_bpf_tcp_ca(void)
 {
 	if (test__start_subtest("dctcp"))
 		test_dctcp();
+	if (test__start_subtest("cubic"))
+		test_cubic();
 }