bpf: selftest: Use bpf_skc_to_tcp_sock() in the sock_fields test

This test uses bpf_skc_to_tcp_sock() to get a kernel tcp_sock ptr "ktp".
Access the ktp->lsndtime and also pass ktp to bpf_sk_storage_get().

It also exercises the bpf_sk_cgroup_id() and bpf_sk_ancestor_cgroup_id()
with the "ktp". To do that, a parent cgroup and a child cgroup are
created. The bpf prog is attached to the child cgroup.

Signed-off-by: Martin KaFai Lau <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

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

···
 	__u32 cnt;
 };
 
-#define TEST_CGROUP "/test-bpf-sock-fields"
+#define PARENT_CGROUP	"/test-bpf-sock-fields"
+#define CHILD_CGROUP	"/test-bpf-sock-fields/child"
 #define DATA "Hello BPF!"
 #define DATA_LEN sizeof(DATA)
 
···
 static int sk_pkt_out_cnt10_fd;
 struct test_sock_fields *skel;
 static int sk_pkt_out_cnt_fd;
+static __u64 parent_cg_id;
+static __u64 child_cg_id;
 static int linum_map_fd;
 static __u32 duration;
 
···
 	      "srv_sk", "Unexpected. Check srv_sk output. egress_linum:%u\n",
 	      egress_linum);
 
+	CHECK(!skel->bss->lsndtime, "srv_tp", "Unexpected lsndtime:0\n");
+
 	CHECK(cli_sk.state == 10 ||
 	      !cli_sk.state ||
 	      cli_sk.family != AF_INET6 ||
···
 	      cli_tp.bytes_received < 2 * DATA_LEN,
 	      "cli_tp", "Unexpected. Check cli_tp output. egress_linum:%u\n",
 	      egress_linum);
+
+	CHECK(skel->bss->parent_cg_id != parent_cg_id,
+	      "parent_cg_id", "%zu != %zu\n",
+	      (size_t)skel->bss->parent_cg_id, (size_t)parent_cg_id);
+
+	CHECK(skel->bss->child_cg_id != child_cg_id,
+	      "child_cg_id", "%zu != %zu\n",
+	       (size_t)skel->bss->child_cg_id, (size_t)child_cg_id);
 }
 
 static void check_sk_pkt_out_cnt(int accept_fd, int cli_fd)
···
 void test_sock_fields(void)
 {
 	struct bpf_link *egress_link = NULL, *ingress_link = NULL;
-	int cgroup_fd;
+	int parent_cg_fd = -1, child_cg_fd = -1;
 
 	/* Create a cgroup, get fd, and join it */
-	cgroup_fd = test__join_cgroup(TEST_CGROUP);
-	if (CHECK_FAIL(cgroup_fd < 0))
+	parent_cg_fd = test__join_cgroup(PARENT_CGROUP);
+	if (CHECK_FAIL(parent_cg_fd < 0))
 		return;
+	parent_cg_id = get_cgroup_id(PARENT_CGROUP);
+	if (CHECK_FAIL(!parent_cg_id))
+		goto done;
+
+	child_cg_fd = test__join_cgroup(CHILD_CGROUP);
+	if (CHECK_FAIL(child_cg_fd < 0))
+		goto done;
+	child_cg_id = get_cgroup_id(CHILD_CGROUP);
+	if (CHECK_FAIL(!child_cg_id))
+		goto done;
 
 	skel = test_sock_fields__open_and_load();
 	if (CHECK(!skel, "test_sock_fields__open_and_load", "failed\n"))
 		goto done;
 
 	egress_link = bpf_program__attach_cgroup(skel->progs.egress_read_sock_fields,
-						 cgroup_fd);
+						 child_cg_fd);
 	if (CHECK(IS_ERR(egress_link), "attach_cgroup(egress)", "err:%ld\n",
 		  PTR_ERR(egress_link)))
 		goto done;
 
 	ingress_link = bpf_program__attach_cgroup(skel->progs.ingress_read_sock_fields,
-						  cgroup_fd);
+						  child_cg_fd);
 	if (CHECK(IS_ERR(ingress_link), "attach_cgroup(ingress)", "err:%ld\n",
 		  PTR_ERR(ingress_link)))
 		goto done;
···
 	bpf_link__destroy(egress_link);
 	bpf_link__destroy(ingress_link);
 	test_sock_fields__destroy(skel);
-	close(cgroup_fd);
+	if (child_cg_fd != -1)
+		close(child_cg_fd);
+	if (parent_cg_fd != -1)
+		close(parent_cg_fd);
 }

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

···
 
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
+#include "bpf_tcp_helpers.h"
 
 enum bpf_linum_array_idx {
 	EGRESS_LINUM_IDX,
···
 struct bpf_sock listen_sk = {};
 struct bpf_sock srv_sk = {};
 struct bpf_sock cli_sk = {};
+__u64 parent_cg_id = 0;
+__u64 child_cg_id = 0;
+__u64 lsndtime = 0;
 
 static bool is_loopback6(__u32 *a6)
 {
···
 	struct bpf_tcp_sock *tp, *tp_ret;
 	struct bpf_sock *sk, *sk_ret;
 	__u32 linum, linum_idx;
+	struct tcp_sock *ktp;
 
 	linum_idx = EGRESS_LINUM_IDX;
 
···
 	tpcpy(tp_ret, tp);
 
 	if (sk_ret == &srv_sk) {
+		ktp = bpf_skc_to_tcp_sock(sk);
+
+		if (!ktp)
+			RET_LOG();
+
+		lsndtime = ktp->lsndtime;
+
+		child_cg_id = bpf_sk_cgroup_id(ktp);
+		if (!child_cg_id)
+			RET_LOG();
+
+		parent_cg_id = bpf_sk_ancestor_cgroup_id(ktp, 2);
+		if (!parent_cg_id)
+			RET_LOG();
+
 		/* The userspace has created it for srv sk */
-		pkt_out_cnt = bpf_sk_storage_get(&sk_pkt_out_cnt, sk, 0, 0);
-		pkt_out_cnt10 = bpf_sk_storage_get(&sk_pkt_out_cnt10, sk,
+		pkt_out_cnt = bpf_sk_storage_get(&sk_pkt_out_cnt, ktp, 0, 0);
+		pkt_out_cnt10 = bpf_sk_storage_get(&sk_pkt_out_cnt10, ktp,
 						   0, 0);
 	} else {
 		pkt_out_cnt = bpf_sk_storage_get(&sk_pkt_out_cnt, sk,