selftests/bpf: Generalize helpers to control background listener

Move the following routines that let us start a background listener
thread and connect to a server by fd to the test_prog:
* start_server - socket+bind+listen
* connect_to_fd - connect to the server identified by fd

These will be used in the next commit.

Also, extend these helpers to support AF_INET6 and accept the family
as an argument.

v5:
* drop pthread.h (Martin KaFai Lau)
* add SO_SNDTIMEO (Martin KaFai Lau)

v4:
* export extra helper to start server without a thread (Martin KaFai Lau)
* tcp_rtt is no longer starting background thread (Martin KaFai Lau)

v2:
* put helpers into network_helpers.c (Andrii Nakryiko)

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrey Ignatov <rdna@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200508174611.228805-2-sdf@google.com

tools/testing/selftests/bpf/network_helpers.c

@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <linux/err.h>
+#include <linux/in.h>
+#include <linux/in6.h>
+
+#include "network_helpers.h"
+
+#define clean_errno() (errno == 0 ? "None" : strerror(errno))
+#define log_err(MSG, ...) fprintf(stderr, "(%s:%d: errno: %s) " MSG "\n", \
+	__FILE__, __LINE__, clean_errno(), ##__VA_ARGS__)
+
+int start_server(int family, int type)
+{
+	struct sockaddr_storage addr = {};
+	socklen_t len;
+	int fd;
+
+	if (family == AF_INET) {
+		struct sockaddr_in *sin = (void *)&addr;
+
+		sin->sin_family = AF_INET;
+		len = sizeof(*sin);
+	} else {
+		struct sockaddr_in6 *sin6 = (void *)&addr;
+
+		sin6->sin6_family = AF_INET6;
+		len = sizeof(*sin6);
+	}
+
+	fd = socket(family, type | SOCK_NONBLOCK, 0);
+	if (fd < 0) {
+		log_err("Failed to create server socket");
+		return -1;
+	}
+
+	if (bind(fd, (const struct sockaddr *)&addr, len) < 0) {
+		log_err("Failed to bind socket");
+		close(fd);
+		return -1;
+	}
+
+	if (type == SOCK_STREAM) {
+		if (listen(fd, 1) < 0) {
+			log_err("Failed to listed on socket");
+			close(fd);
+			return -1;
+		}
+	}
+
+	return fd;
+}
+
+static const struct timeval timeo_sec = { .tv_sec = 3 };
+static const size_t timeo_optlen = sizeof(timeo_sec);
+
+int connect_to_fd(int family, int type, int server_fd)
+{
+	struct sockaddr_storage addr;
+	socklen_t len = sizeof(addr);
+	int fd;
+
+	fd = socket(family, type, 0);
+	if (fd < 0) {
+		log_err("Failed to create client socket");
+		return -1;
+	}
+
+	if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeo_sec, timeo_optlen)) {
+		log_err("Failed to set SO_RCVTIMEO");
+		goto out;
+	}
+
+	if (getsockname(server_fd, (struct sockaddr *)&addr, &len)) {
+		log_err("Failed to get server addr");
+		goto out;
+	}
+
+	if (connect(fd, (const struct sockaddr *)&addr, len) < 0) {
+		log_err("Fail to connect to server with family %d", family);
+		goto out;
+	}
+
+	return fd;
+
+out:
+	close(fd);
+	return -1;
+}