selftests/bpf: Systematically add SO_REUSEADDR in start_server_addr

Some tests have to stop/start a server multiple time with the same
listening address. Doing so without SO_REUSADDR leads to failures due to
the socket still being in TIME_WAIT right after the first instance
stop/before the second instance start. Instead of letting each test
manually set SO_REUSEADDR on their servers, it can be done automatically
by start_server_addr for all tests (and without any major downside).

Enforce SO_REUSEADDR in start_server_addr for all tests.

Signed-off-by: Alexis Lothoré (eBPF Foundation) <[email protected]>
Signed-off-by: Martin KaFai Lau <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: Tropicao

tools/testing/selftests/bpf/network_helpers.c

@@ -97,7 +97,7 @@ int settimeo(int fd, int timeout_ms)
 int start_server_addr(int type, const struct sockaddr_storage *addr, socklen_t addrlen,
 		      const struct network_helper_opts *opts)
 {
-	int fd;
+	int on = 1, fd;
 
 	if (!opts)
 		opts = &default_opts;
@@ -111,6 +111,12 @@ int start_server_addr(int type, const struct sockaddr_storage *addr, socklen_t a
 	if (settimeo(fd, opts->timeout_ms))
 		goto error_close;
 
+	if (type == SOCK_STREAM &&
+	    setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on))) {
+		log_err("Failed to enable SO_REUSEADDR");
+		goto error_close;
+	}
+
 	if (opts->post_socket_cb &&
 	    opts->post_socket_cb(fd, opts->cb_opts)) {
 		log_err("Failed to call post_socket_cb");