sd-bus: optionally, use inotify to wait for bus sockets to appear

This adds a "watch-bind" feature to sd-bus connections. If set and the
AF_UNIX socket we are connecting to doesn't exist yet, we'll establish
an inotify watch instead, and wait for the socket to appear. In other
words, a missing AF_UNIX just makes connecting slower.

This is useful for daemons such as networkd or resolved that shall be
able to run during early-boot, before dbus-daemon is up, and want to
connect to dbus-daemon as soon as it becomes ready.

1 files changed, 239 insertions, 0 deletions

diff --git a/src/libsystemd/sd-bus/test-bus-watch-bind.c b/src/libsystemd/sd-bus/test-bus-watch-bind.c
new file mode 100644
index 0000000000..aef5ba9486
--- /dev/null
+++ b/src/libsystemd/sd-bus/test-bus-watch-bind.c
@@ -0,0 +1,239 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+/***
+  This file is part of systemd.
+
+  Copyright 2017 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <pthread.h>
+
+#include "sd-bus.h"
+#include "sd-event.h"
+#include "sd-id128.h"
+
+#include "alloc-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "mkdir.h"
+#include "path-util.h"
+#include "random-util.h"
+#include "rm-rf.h"
+#include "socket-util.h"
+#include "string-util.h"
+
+static int method_foobar(sd_bus_message *m, void *userdata, sd_bus_error *ret_error) {
+        log_info("Got Foobar() call.");
+
+        assert_se(sd_event_exit(sd_bus_get_event(sd_bus_message_get_bus(m)), 0) >= 0);
+        return sd_bus_reply_method_return(m, NULL);
+}
+
+static int method_exit(sd_bus_message *m, void *userdata, sd_bus_error *ret_error) {
+        log_info("Got Exit() call");
+        assert_se(sd_event_exit(sd_bus_get_event(sd_bus_message_get_bus(m)), 1) >= 0);
+        return sd_bus_reply_method_return(m, NULL);
+}
+
+static const sd_bus_vtable vtable[] = {
+        SD_BUS_VTABLE_START(0),
+        SD_BUS_METHOD("Foobar", NULL, NULL, method_foobar, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_METHOD("Exit", NULL, NULL, method_exit, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_VTABLE_END,
+};
+
+static void* thread_server(void *p) {
+        _cleanup_free_ char *suffixed = NULL, *suffixed2 = NULL, *d = NULL;
+        _cleanup_close_ int fd = -1;
+        union sockaddr_union u = {
+                .un.sun_family = AF_UNIX,
+        };
+        const char *path = p;
+
+        log_debug("Initializing server");
+
+        /* Let's play some games, by slowly creating the socket directory, and renaming it in the middle */
+        (void) usleep(100 * USEC_PER_MSEC);
+
+        assert_se(mkdir_parents(path, 0755) >= 0);
+        (void) usleep(100 * USEC_PER_MSEC);
+
+        d = dirname_malloc(path);
+        assert_se(d);
+        assert_se(asprintf(&suffixed, "%s.%" PRIx64, d, random_u64()) >= 0);
+        assert_se(rename(d, suffixed) >= 0);
+        (void) usleep(100 * USEC_PER_MSEC);
+
+        assert_se(asprintf(&suffixed2, "%s.%" PRIx64, d, random_u64()) >= 0);
+        assert_se(symlink(suffixed2, d) >= 0);
+        (void) usleep(100 * USEC_PER_MSEC);
+
+        assert_se(symlink(basename(suffixed), suffixed2) >= 0);
+        (void) usleep(100 * USEC_PER_MSEC);
+
+        strncpy(u.un.sun_path, path, sizeof(u.un.sun_path));
+
+        fd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
+        assert_se(fd >= 0);
+
+        assert_se(bind(fd, &u.sa, SOCKADDR_UN_LEN(u.un)) >= 0);
+        usleep(100 * USEC_PER_MSEC);
+
+        assert_se(listen(fd, SOMAXCONN) >= 0);
+        usleep(100 * USEC_PER_MSEC);
+
+        assert_se(touch(path) >= 0);
+        usleep(100 * USEC_PER_MSEC);
+
+        log_debug("Initialized server");
+
+        for (;;) {
+                _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+                _cleanup_(sd_event_unrefp) sd_event *event = NULL;
+                sd_id128_t id;
+                int bus_fd, code;
+
+                assert_se(sd_id128_randomize(&id) >= 0);
+
+                assert_se(sd_event_new(&event) >= 0);
+
+                bus_fd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
+                assert_se(bus_fd >= 0);
+
+                log_debug("Accepted server connection");
+
+                assert_se(sd_bus_new(&bus) >= 0);
+                assert_se(sd_bus_set_description(bus, "server") >= 0);
+                assert_se(sd_bus_set_fd(bus, bus_fd, bus_fd) >= 0);
+                assert_se(sd_bus_set_server(bus, true, id) >= 0);
+                /* assert_se(sd_bus_set_anonymous(bus, true) >= 0); */
+
+                assert_se(sd_bus_attach_event(bus, event, 0) >= 0);
+
+                assert_se(sd_bus_add_object_vtable(bus, NULL, "/foo", "foo.TestInterface", vtable, NULL) >= 0);
+
+                assert_se(sd_bus_start(bus) >= 0);
+
+                assert_se(sd_event_loop(event) >= 0);
+
+                assert_se(sd_event_get_exit_code(event, &code) >= 0);
+
+                if (code > 0)
+                        break;
+        }
+
+        log_debug("Server done");
+
+        return NULL;
+}
+
+static void* thread_client1(void *p) {
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        const char *path = p, *t;
+        int r;
+
+        log_debug("Initializing client1");
+
+        assert_se(sd_bus_new(&bus) >= 0);
+        assert_se(sd_bus_set_description(bus, "client1") >= 0);
+
+        t = strjoina("unix:path=", path);
+        assert_se(sd_bus_set_address(bus, t) >= 0);
+        assert_se(sd_bus_set_watch_bind(bus, true) >= 0);
+        assert_se(sd_bus_start(bus) >= 0);
+
+        r = sd_bus_call_method(bus, "foo.bar", "/foo", "foo.TestInterface", "Foobar", &error, NULL, NULL);
+        assert_se(r >= 0);
+
+        log_debug("Client1 done");
+
+        return NULL;
+}
+
+static int client2_callback(sd_bus_message *m, void *userdata, sd_bus_error *ret_error) {
+        assert_se(sd_bus_message_is_method_error(m, NULL) == 0);
+        assert_se(sd_event_exit(sd_bus_get_event(sd_bus_message_get_bus(m)), 0) >= 0);
+        return 0;
+}
+
+static void* thread_client2(void *p) {
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        _cleanup_(sd_event_unrefp) sd_event *event = NULL;
+        const char *path = p, *t;
+
+        log_debug("Initializing client2");
+
+        assert_se(sd_event_new(&event) >= 0);
+        assert_se(sd_bus_new(&bus) >= 0);
+        assert_se(sd_bus_set_description(bus, "client2") >= 0);
+
+        t = strjoina("unix:path=", path);
+        assert_se(sd_bus_set_address(bus, t) >= 0);
+        assert_se(sd_bus_set_watch_bind(bus, true) >= 0);
+        assert_se(sd_bus_attach_event(bus, event, 0) >= 0);
+        assert_se(sd_bus_start(bus) >= 0);
+
+        assert_se(sd_bus_call_method_async(bus, NULL, "foo.bar", "/foo", "foo.TestInterface", "Foobar", client2_callback, NULL, NULL) >= 0);
+
+        assert_se(sd_event_loop(event) >= 0);
+
+        log_debug("Client2 done");
+
+        return NULL;
+}
+
+static void request_exit(const char *path) {
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        const char *t;
+
+        assert_se(sd_bus_new(&bus) >= 0);
+
+        t = strjoina("unix:path=", path);
+        assert_se(sd_bus_set_address(bus, t) >= 0);
+        assert_se(sd_bus_set_watch_bind(bus, true) >= 0);
+        assert_se(sd_bus_set_description(bus, "request-exit") >= 0);
+        assert_se(sd_bus_start(bus) >= 0);
+
+        assert_se(sd_bus_call_method(bus, "foo.bar", "/foo", "foo.TestInterface", "Exit", NULL, NULL, NULL) >= 0);
+}
+
+int main(int argc, char *argv[]) {
+        _cleanup_(rm_rf_physical_and_freep) char *d = NULL;
+        pthread_t server, client1, client2;
+        char *path;
+
+        log_set_max_level(LOG_DEBUG);
+
+        /* We use /dev/shm here rather than /tmp, since some weird distros might set up /tmp as some weird fs that
+         * doesn't support inotify properly. */
+        assert_se(mkdtemp_malloc("/dev/shm/systemd-watch-bind-XXXXXX", &d) >= 0);
+
+        path = strjoina(d, "/this/is/a/socket");
+
+        assert_se(pthread_create(&server, NULL, thread_server, path) == 0);
+        assert_se(pthread_create(&client1, NULL, thread_client1, path) == 0);
+        assert_se(pthread_create(&client2, NULL, thread_client2, path) == 0);
+
+        assert_se(pthread_join(client1, NULL) == 0);
+        assert_se(pthread_join(client2, NULL) == 0);
+
+        request_exit(path);
+
+        assert_se(pthread_join(server, NULL) == 0);
+
+        return 0;
+}