Merge !1608: daemon: add sd_notify alternative

NEWS

@@ -4,6 +4,7 @@ Knot Resolver 6.0.10 (202y-mm-dd)
 Improvements
 ------------
 - avoid multiple log lines when IPv6 isn't available (!1633)
+- manager: fix startup on Linux without libsystemd (!1608)
 
 
 Knot Resolver 6.0.9 (2024-11-11)

daemon/main.c

@@ -38,6 +38,8 @@
 #include <uv.h>
 #if ENABLE_LIBSYSTEMD
 #include <systemd/sd-daemon.h>
+#else
+static int notify_ready(const char *state);
 #endif
 #include <libknot/error.h>
 
@@ -193,6 +195,8 @@ static int run_worker(uv_loop_t *loop, struct args *args)
 	/* Notify supervisor. */
 #if ENABLE_LIBSYSTEMD
 	sd_notify(0, "READY=1");
+#else
+	notify_ready("READY=1");
 #endif
 	/* Run event loop */
 	uv_run(loop, UV_RUN_DEFAULT);
@@ -382,6 +386,47 @@ static int start_listening(flagged_fd_array_t *fds) {
 	return some_bad_ret;
 }
 
+#if !ENABLE_LIBSYSTEMD
+/* Notify supervisord about successful inicialization
+ * @note tested only on an abstract address in $NOTIFY_SOCKET*/
+static int notify_ready(const char *state)
+{
+	int sockfd;
+	struct sockaddr_un addr;
+	char *socket_path = getenv("NOTIFY_SOCKET");
+	if (!socket_path) {
+		kr_log_error(WORKER, "Failed retrieving env variable $NOTIFY_SOCKET\n");
+		return EXIT_FAILURE;
+	}
+	if ((sockfd = socket(AF_UNIX, SOCK_DGRAM, 0)) == -1) {
+		kr_log_error(WORKER, "Failed to create unix socket at $NOTIFY_SOCKET ('%s'): %s\n",
+				socket_path, strerror(errno));
+		return EXIT_FAILURE;
+	}
+
+	addr.sun_family = AF_UNIX;
+
+	int addrlen;
+	if (socket_path[0] == '@') {
+		addr.sun_path[0] = '\0';
+		strncpy(&addr.sun_path[1], socket_path + 1, sizeof(addr.sun_path) - 2);
+		addrlen = offsetof(struct sockaddr_un, sun_path) + strlen(addr.sun_path + 1) + 1;
+	} else {
+		strncpy(addr.sun_path, socket_path, sizeof(addr.sun_path) - 1);
+		addrlen = offsetof(struct sockaddr_un, sun_path) + strlen(addr.sun_path) + 1;
+	}
+	if (sendto(sockfd, state, strlen(state), 0, &addr, addrlen) == -1) {
+		kr_log_error(WORKER, "Failed to send notify message to '%s': %s\n",
+			socket_path, strerror(errno));
+		close(sockfd);
+		return EXIT_FAILURE;
+	}
+
+	close(sockfd);
+	return kr_ok();
+}
+#endif /* if !ENABLE_LIBSYSTEMD */
+
 /* Drop POSIX 1003.1e capabilities. */
 static void drop_capabilities(void)
 {