selftests/bpf: Use post_socket_cb in connect_to_fd_opts

Since the post_socket_cb() callback is added in struct network_helper_opts,
it's make sense to use it not only in __start_server(), but also in
connect_to_fd_opts(). Then it can be used to set TCP_CONGESTION sockopt.

Add a "void *" type member cb_opts into struct network_helper_opts, and add
a new struct named cb_opts in prog_tests/bpf_tcp_ca.c, then cc can be moved
into struct cb_opts from network_helper_opts. Define a new callback cc_cb()
to set TCP_CONGESTION sockopt, and set it to post_socket_cb pointer of opts.
Define a new cb_opts cubic, set it to cb_opts of opts. Pass this opts to
connect_to_fd_opts() in test_dctcp_fallback().
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Link: https://lore.kernel.org/r/b512bb8d8f6854c9ea5c409b69d1bf37c6f272c6.1716638248.git.tanggeliang@kylinos.cnSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/testing/selftests/bpf/network_helpers.c

@@ -348,9 +348,8 @@ int connect_to_fd_opts(int server_fd, const struct network_helper_opts *opts)
 	if (settimeo(fd, opts->timeout_ms))
 		goto error_close;
 
-	if (opts->cc && opts->cc[0] &&
-	    setsockopt(fd, SOL_TCP, TCP_CONGESTION, opts->cc,
-		       strlen(opts->cc) + 1))
+	if (opts->post_socket_cb &&
+	    opts->post_socket_cb(fd, opts->cb_opts))
 		goto error_close;
 
 	if (!opts->noconnect)

tools/testing/selftests/bpf/network_helpers.h

@@ -22,13 +22,13 @@ typedef __u16 __sum16;
 #define MAGIC_BYTES 123
 
 struct network_helper_opts {
-	const char *cc;
 	int timeout_ms;
 	bool must_fail;
 	bool noconnect;
 	int type;
 	int proto;
 	int (*post_socket_cb)(int fd, void *opts);
+	void *cb_opts;
 };
 
 /* ipv4 test vector */

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

@@ -23,6 +23,10 @@
 static const unsigned int total_bytes = 10 * 1024 * 1024;
 static int expected_stg = 0xeB9F;
 
+struct cb_opts {
+	const char *cc;
+};
+
 static int settcpca(int fd, const char *tcp_ca)
 {
 	int err;
@@ -81,6 +85,13 @@ static void do_test(const char *tcp_ca, const struct bpf_map *sk_stg_map)
 	close(fd);
 }
 
+static int cc_cb(int fd, void *opts)
+{
+	struct cb_opts *cb_opts = (struct cb_opts *)opts;
+
+	return settcpca(fd, cb_opts->cc);
+}
+
 static void test_cubic(void)
 {
 	struct bpf_cubic *cubic_skel;
@@ -172,10 +183,13 @@ static void test_dctcp_fallback(void)
 {
 	int err, lfd = -1, cli_fd = -1, srv_fd = -1;
 	struct network_helper_opts opts = {
-		.cc = "cubic",
+		.post_socket_cb	= cc_cb,
 	};
 	struct bpf_dctcp *dctcp_skel;
 	struct bpf_link *link = NULL;
+	struct cb_opts cubic = {
+		.cc = "cubic",
+	};
 	char srv_cc[16];
 	socklen_t cc_len = sizeof(srv_cc);
 
@@ -195,6 +209,7 @@ static void test_dctcp_fallback(void)
 	    !ASSERT_OK(settcpca(lfd, "bpf_dctcp"), "lfd=>bpf_dctcp"))
 		goto done;
 
+	opts.cb_opts = &cubic;
 	cli_fd = connect_to_fd_opts(lfd, &opts);
 	if (!ASSERT_GE(cli_fd, 0, "cli_fd"))
 		goto done;