Merge pull request #34799 from YHNdnzj/service-followups

core: follow-ups for live mount

9 files changed, 99 insertions, 101 deletions

diff --git a/src/basic/fs-util.c b/src/basic/fs-util.c
index 7c88e9fef7..db0a316e6d 100644
--- a/src/basic/fs-util.c
+++ b/src/basic/fs-util.c
@@ -694,17 +694,6 @@ int access_fd(int fd, int mode) {
         return 0;
 }
 
-void unlink_tempfilep(char (*p)[]) {
-        assert(p);
-
-        /* If the file is created with mkstemp(), it will (almost always)
-         * change the suffix. Treat this as a sign that the file was
-         * successfully created. We ignore both the rare case where the
-         * original suffix is used and unlink failures. */
-        if (!endswith(*p, ".XXXXXX"))
-                (void) unlink(*p);
-}
-
 int unlinkat_deallocate(int fd, const char *name, UnlinkDeallocateFlags flags) {
         _cleanup_close_ int truncate_fd = -EBADF;
         struct stat st;
diff --git a/src/basic/fs-util.h b/src/basic/fs-util.h
index 93af685eef..028c86a3b2 100644
--- a/src/basic/fs-util.h
+++ b/src/basic/fs-util.h
@@ -112,8 +112,6 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(char*, unlink_and_free);
 
 int access_fd(int fd, int mode);
 
-void unlink_tempfilep(char (*p)[]);
-
 typedef enum UnlinkDeallocateFlags {
         UNLINK_REMOVEDIR = 1 << 0,
         UNLINK_ERASE     = 1 << 1,
diff --git a/src/basic/tmpfile-util.c b/src/basic/tmpfile-util.c
index 3a3f7dcc0f..5addd8e8a9 100644
--- a/src/basic/tmpfile-util.c
+++ b/src/basic/tmpfile-util.c
@@ -118,6 +118,17 @@ int fmkostemp_safe(char *pattern, const char *mode, FILE **ret_f) {
         return 0;
 }
 
+void unlink_tempfilep(char (*p)[]) {
+        assert(p);
+
+        /* If the file is created with mkstemp(), it will (almost always) change the suffix.
+         * Treat this as a sign that the file was successfully created. We ignore both the rare case
+         * where the original suffix is used and unlink failures. */
+
+        if (!endswith(*p, ".XXXXXX"))
+                (void) unlink(*p);
+}
+
 static int tempfn_build(const char *p, const char *pre, const char *post, bool child, char **ret) {
         _cleanup_free_ char *d = NULL, *fn = NULL, *nf = NULL, *result = NULL;
         size_t len_pre, len_post, len_add;
diff --git a/src/basic/tmpfile-util.h b/src/basic/tmpfile-util.h
index 8c917c0680..408f80e147 100644
--- a/src/basic/tmpfile-util.h
+++ b/src/basic/tmpfile-util.h
@@ -18,6 +18,8 @@ static inline int fopen_temporary_child(const char *path, FILE **ret_file, char
 int mkostemp_safe(char *pattern);
 int fmkostemp_safe(char *pattern, const char *mode, FILE**_f);
 
+void unlink_tempfilep(char (*p)[]);
+
 int tempfn_xxxxxx(const char *p, const char *extra, char **ret);
 int tempfn_random(const char *p, const char *extra, char **ret);
 int tempfn_random_child(const char *p, const char *extra, char **ret);
diff --git a/src/core/service.c b/src/core/service.c
index dfad574e65..1ac158f1ea 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -64,6 +64,7 @@ static const UnitActiveState state_translation_table[_SERVICE_STATE_MAX] = {
         [SERVICE_RELOAD]                     = UNIT_RELOADING,
         [SERVICE_RELOAD_SIGNAL]              = UNIT_RELOADING,
         [SERVICE_RELOAD_NOTIFY]              = UNIT_RELOADING,
+        [SERVICE_MOUNTING]                   = UNIT_REFRESHING,
         [SERVICE_STOP]                       = UNIT_DEACTIVATING,
         [SERVICE_STOP_WATCHDOG]              = UNIT_DEACTIVATING,
         [SERVICE_STOP_SIGTERM]               = UNIT_DEACTIVATING,
@@ -79,7 +80,6 @@ static const UnitActiveState state_translation_table[_SERVICE_STATE_MAX] = {
         [SERVICE_AUTO_RESTART]               = UNIT_ACTIVATING,
         [SERVICE_AUTO_RESTART_QUEUED]        = UNIT_ACTIVATING,
         [SERVICE_CLEANING]                   = UNIT_MAINTENANCE,
-        [SERVICE_MOUNTING]                   = UNIT_REFRESHING,
 };
 
 /* For Type=idle we never want to delay any other jobs, hence we
@@ -95,6 +95,7 @@ static const UnitActiveState state_translation_table_idle[_SERVICE_STATE_MAX] =
         [SERVICE_RELOAD]                     = UNIT_RELOADING,
         [SERVICE_RELOAD_SIGNAL]              = UNIT_RELOADING,
         [SERVICE_RELOAD_NOTIFY]              = UNIT_RELOADING,
+        [SERVICE_MOUNTING]                   = UNIT_REFRESHING,
         [SERVICE_STOP]                       = UNIT_DEACTIVATING,
         [SERVICE_STOP_WATCHDOG]              = UNIT_DEACTIVATING,
         [SERVICE_STOP_SIGTERM]               = UNIT_DEACTIVATING,
@@ -110,7 +111,6 @@ static const UnitActiveState state_translation_table_idle[_SERVICE_STATE_MAX] =
         [SERVICE_AUTO_RESTART]               = UNIT_ACTIVATING,
         [SERVICE_AUTO_RESTART_QUEUED]        = UNIT_ACTIVATING,
         [SERVICE_CLEANING]                   = UNIT_MAINTENANCE,
-        [SERVICE_MOUNTING]                   = UNIT_REFRESHING,
 };
 
 static int service_dispatch_inotify_io(sd_event_source *source, int fd, uint32_t events, void *userdata);
@@ -136,9 +136,10 @@ static bool SERVICE_STATE_WITH_CONTROL_PROCESS(ServiceState state) {
                       SERVICE_CONDITION,
                       SERVICE_START_PRE, SERVICE_START, SERVICE_START_POST,
                       SERVICE_RELOAD, SERVICE_RELOAD_SIGNAL, SERVICE_RELOAD_NOTIFY,
+                      SERVICE_MOUNTING,
                       SERVICE_STOP, SERVICE_STOP_WATCHDOG, SERVICE_STOP_SIGTERM, SERVICE_STOP_SIGKILL, SERVICE_STOP_POST,
                       SERVICE_FINAL_WATCHDOG, SERVICE_FINAL_SIGTERM, SERVICE_FINAL_SIGKILL,
-                      SERVICE_CLEANING, SERVICE_MOUNTING);
+                      SERVICE_CLEANING);
 }
 
 static void service_init(Unit *u) {
@@ -982,8 +983,8 @@ static void service_dump(Unit *u, FILE *f, const char *prefix) {
                 prefix, service_state_to_string(s->state),
                 prefix, service_result_to_string(s->result),
                 prefix, service_result_to_string(s->reload_result),
-                prefix, service_result_to_string(s->clean_result),
                 prefix, service_result_to_string(s->live_mount_result),
+                prefix, service_result_to_string(s->clean_result),
                 prefix, yes_no(s->permissions_start_only),
                 prefix, yes_no(s->root_directory_start_only),
                 prefix, yes_no(s->remain_after_exit),
@@ -1261,7 +1262,7 @@ static void service_search_main_pid(Service *s) {
         r = unit_watch_pidref(UNIT(s), &s->main_pid, /* exclusive= */ false);
         if (r < 0)
                 /* FIXME: we need to do something here */
-                log_unit_warning_errno(UNIT(s), r, "Failed to watch PID "PID_FMT" from: %m", s->main_pid.pid);
+                log_unit_warning_errno(UNIT(s), r, "Failed to watch main PID "PID_FMT": %m", s->main_pid.pid);
 }
 
 static void service_set_state(Service *s, ServiceState state) {
@@ -1283,10 +1284,10 @@ static void service_set_state(Service *s, ServiceState state) {
                     SERVICE_CONDITION, SERVICE_START_PRE, SERVICE_START, SERVICE_START_POST,
                     SERVICE_RUNNING,
                     SERVICE_RELOAD, SERVICE_RELOAD_SIGNAL, SERVICE_RELOAD_NOTIFY,
+                    SERVICE_MOUNTING,
                     SERVICE_STOP, SERVICE_STOP_WATCHDOG, SERVICE_STOP_SIGTERM, SERVICE_STOP_SIGKILL, SERVICE_STOP_POST,
                     SERVICE_FINAL_WATCHDOG, SERVICE_FINAL_SIGTERM, SERVICE_FINAL_SIGKILL,
                     SERVICE_AUTO_RESTART,
-                    SERVICE_MOUNTING,
                     SERVICE_CLEANING))
                 s->timer_event_source = sd_event_source_disable_unref(s->timer_event_source);
 
@@ -1315,6 +1316,9 @@ static void service_set_state(Service *s, ServiceState state) {
         if (!IN_SET(state, SERVICE_START_POST, SERVICE_RUNNING, SERVICE_RELOAD, SERVICE_RELOAD_SIGNAL, SERVICE_RELOAD_NOTIFY, SERVICE_MOUNTING))
                 service_stop_watchdog(s);
 
+        if (state != SERVICE_MOUNTING) /* Just in case */
+                s->mount_request = sd_bus_message_unref(s->mount_request);
+
         if (state == SERVICE_EXITED && !MANAGER_IS_RELOADING(u->manager)) {
                 /* For the inactive states unit_notify() will trim the cgroup. But for exit we have to
                  * do that ourselves... */
@@ -1336,9 +1340,6 @@ static void service_set_state(Service *s, ServiceState state) {
                         unit_destroy_runtime_data(u, &s->exec_context);
         }
 
-        if (state != SERVICE_MOUNTING) /* Just in case */
-                s->mount_request = sd_bus_message_unref(s->mount_request);
-
         if (old_state != state)
                 log_unit_debug(u, "Changed %s -> %s", service_state_to_string(old_state), service_state_to_string(state));
 
@@ -1357,6 +1358,7 @@ static usec_t service_coldplug_timeout(Service *s) {
         case SERVICE_RELOAD:
         case SERVICE_RELOAD_SIGNAL:
         case SERVICE_RELOAD_NOTIFY:
+        case SERVICE_MOUNTING:
                 return usec_add(UNIT(s)->state_change_timestamp.monotonic, s->timeout_start_usec);
 
         case SERVICE_RUNNING:
@@ -1380,9 +1382,6 @@ static usec_t service_coldplug_timeout(Service *s) {
         case SERVICE_CLEANING:
                 return usec_add(UNIT(s)->state_change_timestamp.monotonic, s->exec_context.timeout_clean_usec);
 
-        case SERVICE_MOUNTING:
-                return usec_add(UNIT(s)->state_change_timestamp.monotonic, s->timeout_start_usec);
-
         default:
                 return USEC_INFINITY;
         }
@@ -2889,14 +2888,16 @@ static int service_start(Unit *u) {
         return 1;
 }
 
-static void service_mount_request_reply(Service *s, bool success, const char *error) {
+static void service_live_mount_finish(Service *s, ServiceResult f, const char *error) {
         assert(s);
         assert(error);
 
+        s->live_mount_result = f;
+
         if (!s->mount_request)
                 return;
 
-        if (success) {
+        if (f == SERVICE_SUCCESS) {
                 (void) sd_bus_reply_method_return(s->mount_request, NULL);
                 log_unit_debug(UNIT(s),
                                "'%s' method succeeded",
@@ -2941,7 +2942,7 @@ static int service_stop(Unit *u) {
 
         case SERVICE_MOUNTING:
                 service_kill_control_process(s);
-                service_mount_request_reply(s, /* success= */ false, BUS_ERROR_UNIT_INACTIVE);
+                service_live_mount_finish(s, SERVICE_FAILURE_PROTOCOL, BUS_ERROR_UNIT_INACTIVE);
                 _fallthrough_;
         case SERVICE_CONDITION:
         case SERVICE_START_PRE:
@@ -3087,6 +3088,7 @@ static int service_serialize(Unit *u, FILE *f, FDSet *fds) {
         (void) serialize_item(f, "state", service_state_to_string(s->state));
         (void) serialize_item(f, "result", service_result_to_string(s->result));
         (void) serialize_item(f, "reload-result", service_result_to_string(s->reload_result));
+        (void) serialize_item(f, "live-mount-result", service_result_to_string(s->live_mount_result));
 
         (void) serialize_pidref(f, fds, "control-pid", &s->control_pid);
         if (s->main_pid_known)
@@ -3315,7 +3317,7 @@ static int service_deserialize_item(Unit *u, const char *key, const char *value,
 
                 state = service_state_from_string(value);
                 if (state < 0)
-                        log_unit_debug(u, "Failed to parse state value: %s", value);
+                        log_unit_debug_errno(u, state, "Failed to parse state value: %s", value);
                 else
                         s->deserialized_state = state;
         } else if (streq(key, "result")) {
@@ -3323,7 +3325,7 @@ static int service_deserialize_item(Unit *u, const char *key, const char *value,
 
                 f = service_result_from_string(value);
                 if (f < 0)
-                        log_unit_debug(u, "Failed to parse result value: %s", value);
+                        log_unit_debug_errno(u, f, "Failed to parse result value: %s", value);
                 else if (f != SERVICE_SUCCESS)
                         s->result = f;
 
@@ -3332,10 +3334,19 @@ static int service_deserialize_item(Unit *u, const char *key, const char *value,
 
                 f = service_result_from_string(value);
                 if (f < 0)
-                        log_unit_debug(u, "Failed to parse reload result value: %s", value);
+                        log_unit_debug_errno(u, f, "Failed to parse reload result value: %s", value);
                 else if (f != SERVICE_SUCCESS)
                         s->reload_result = f;
 
+        } else if (streq(key, "live-mount-result")) {
+                ServiceResult f;
+
+                f = service_result_from_string(value);
+                if (f < 0)
+                        log_unit_debug_errno(u, f, "Failed to parse live mount result value: %s", value);
+                else if (f != SERVICE_SUCCESS)
+                        s->live_mount_result = f;
+
         } else if (streq(key, "control-pid")) {
 
                 if (!pidref_is_set(&s->control_pid))
@@ -4185,6 +4196,12 @@ static void service_sigchld_event(Unit *u, pid_t pid, int code, int status) {
                                         service_enter_running(s, SERVICE_SUCCESS);
                                 break;
 
+                        case SERVICE_MOUNTING:
+                                service_live_mount_finish(s, f, SD_BUS_ERROR_FAILED);
+
+                                service_enter_running(s, SERVICE_SUCCESS);
+                                break;
+
                         case SERVICE_STOP:
                                 service_enter_signal(s, SERVICE_STOP_SIGTERM, f);
                                 break;
@@ -4219,14 +4236,6 @@ static void service_sigchld_event(Unit *u, pid_t pid, int code, int status) {
                                 service_enter_dead(s, SERVICE_SUCCESS, false);
                                 break;
 
-                        case SERVICE_MOUNTING:
-                                s->live_mount_result = f;
-
-                                service_mount_request_reply(s, f == SERVICE_SUCCESS, SD_BUS_ERROR_FAILED);
-
-                                service_enter_running(s, SERVICE_SUCCESS);
-                                break;
-
                         default:
                                 assert_not_reached();
                         }
@@ -4303,8 +4312,7 @@ static int service_dispatch_timer(sd_event_source *source, usec_t usec, void *us
         case SERVICE_MOUNTING:
                 log_unit_warning(UNIT(s), "Mount operation timed out. Killing mount process.");
                 service_kill_control_process(s);
-                s->live_mount_result = SERVICE_FAILURE_TIMEOUT;
-                service_mount_request_reply(s, /* success= */ false, SD_BUS_ERROR_TIMEOUT);
+                service_live_mount_finish(s, SERVICE_FAILURE_TIMEOUT, SD_BUS_ERROR_TIMEOUT);
                 service_enter_running(s, SERVICE_SUCCESS);
                 break;
 
@@ -5013,8 +5021,8 @@ static void service_reset_failed(Unit *u) {
 
         s->result = SERVICE_SUCCESS;
         s->reload_result = SERVICE_SUCCESS;
-        s->clean_result = SERVICE_SUCCESS;
         s->live_mount_result = SERVICE_SUCCESS;
+        s->clean_result = SERVICE_SUCCESS;
         s->n_restarts = 0;
 
         (void) unit_set_debug_invocation(u, /* enable= */ false);
@@ -5159,7 +5167,8 @@ static int service_can_clean(Unit *u, ExecCleanMask *ret) {
         return 0;
 }
 
-static int service_live_mount(Unit *u,
+static int service_live_mount(
+                Unit *u,
                 const char *src,
                 const char *dst,
                 sd_bus_message *message,
@@ -5167,9 +5176,8 @@ static int service_live_mount(Unit *u,
                 const MountOptions *options,
                 sd_bus_error *error) {
 
-        _cleanup_(pidref_done) PidRef worker = PIDREF_NULL;
         Service *s = ASSERT_PTR(SERVICE(u));
-        const char *propagate_directory;
+        _cleanup_(pidref_done) PidRef worker = PIDREF_NULL;
         int r;
 
         assert(u);
@@ -5180,7 +5188,7 @@ static int service_live_mount(Unit *u,
         assert(!s->mount_request);
 
         if (s->state != SERVICE_RUNNING || !pidref_is_set(&s->main_pid)) {
-                log_unit_warning(u, "Service is not running, cannot live mount");
+                log_unit_warning(u, "Service is not running, cannot live mount.");
                 return sd_bus_error_setf(
                                 error,
                                 BUS_ERROR_UNIT_INACTIVE,
@@ -5191,7 +5199,7 @@ static int service_live_mount(Unit *u,
         }
 
         if (mount_point_is_credentials(u->manager->prefix[EXEC_DIRECTORY_RUNTIME], dst)) {
-                log_unit_warning(u, "Refusing to live mount over credential mount '%s'", dst);
+                log_unit_warning(u, "Refusing to live mount over credential mount '%s'.", dst);
                 return sd_bus_error_setf(
                                 error,
                                 SD_BUS_ERROR_INVALID_ARGS,
@@ -5202,7 +5210,7 @@ static int service_live_mount(Unit *u,
         }
 
         if (path_startswith_strv(dst, s->exec_context.inaccessible_paths)) {
-                log_unit_warning(u, "%s is not accessible to this unit, cannot live mount", dst);
+                log_unit_warning(u, "%s is not accessible to this unit, cannot live mount.", dst);
                 return sd_bus_error_setf(
                                 error,
                                 SD_BUS_ERROR_INVALID_ARGS,
@@ -5219,18 +5227,14 @@ static int service_live_mount(Unit *u,
 
         r = service_arm_timer(s, /* relative= */ true, s->timeout_start_usec);
         if (r < 0) {
-                log_unit_warning_errno(u, r, "Failed to install timer: %m");
-                sd_bus_error_set_errnof(
-                                error,
-                                r,
-                                "Live mounting '%s' on '%s' for unit '%s' cannot be scheduled: failed to install timer",
-                                src,
-                                dst,
-                                u->id);
+                log_unit_error_errno(u, r, "Failed to install timer: %m");
+                sd_bus_error_set_errnof(error, r,
+                                        "Live mounting '%s' on '%s' for unit '%s': failed to install timer: %m",
+                                        src, dst, u->id);
                 goto fail;
         }
 
-        propagate_directory = strjoina("/run/systemd/propagate/", u->id);
+        const char *propagate_directory = strjoina("/run/systemd/propagate/", u->id);
 
         /* Given we are running from PID1, avoid doing potentially heavy I/O operations like opening images
          * directly, and instead fork a worker process. We record the D-Bus message, so that we can reply
@@ -5238,19 +5242,12 @@ static int service_live_mount(Unit *u,
          * resource is available (or the operation failed) once they receive the response. */
         r = unit_fork_helper_process(u, "(sd-mount-in-ns)", /* into_cgroup= */ false, &worker);
         if (r < 0) {
-                log_unit_warning_errno(
-                                u,
-                                r,
-                                "Failed to fork process to mount '%s' on '%s' in unit's namespace: %m",
-                                src,
-                                dst);
-                sd_bus_error_set_errnof(
-                                error,
-                                r,
-                                "Live mounting '%s' on '%s' for unit '%s' cannot be scheduled: failed to fork process",
-                                src,
-                                dst,
-                                u->id);
+                log_unit_error_errno(u, r,
+                                     "Failed to fork process to mount '%s' on '%s' in unit's namespace: %m",
+                                     src, dst);
+                sd_bus_error_set_errnof(error, r,
+                                        "Live mounting '%s' on '%s' for unit '%s': failed to fork off helper process into namespace: %m",
+                                        src, dst, u->id);
                 goto fail;
         }
         if (r == 0) {
@@ -5271,26 +5268,21 @@ static int service_live_mount(Unit *u,
                                         src, dst,
                                         flags);
                 if (r < 0)
-                        log_unit_warning_errno(
-                                        u,
-                                        r,
-                                        "Failed to mount '%s' on '%s' in unit's namespace: %m",
-                                        src,
-                                        dst);
+                        log_unit_error_errno(u, r,
+                                             "Failed to mount '%s' on '%s' in unit's namespace: %m",
+                                             src, dst);
                 else
                         log_unit_debug(u, "Mounted '%s' on '%s' in unit's namespace", src, dst);
+
                 _exit(r < 0 ? EXIT_FAILURE : EXIT_SUCCESS);
         }
 
         r = unit_watch_pidref(u, &worker, /* exclusive= */ true);
         if (r < 0) {
-                sd_bus_error_set_errnof(
-                                error,
-                                r,
-                                "Live mounting '%s' on '%s' for unit '%s' failed: failed to watch worker process",
-                                src,
-                                dst,
-                                u->id);
+                log_unit_warning_errno(u, r, "Failed to watch live mount helper process: %m");
+                sd_bus_error_set_errnof(error, r,
+                                        "Live mounting '%s' on '%s' for unit '%s': failed to watch live mount helper process: %m",
+                                        src, dst, u->id);
                 goto fail;
         }
 
@@ -5301,15 +5293,15 @@ static int service_live_mount(Unit *u,
 
 fail:
         s->live_mount_result = SERVICE_FAILURE_RESOURCES;
-        s->timer_event_source = sd_event_source_disable_unref(s->timer_event_source);
+        service_enter_running(s, SERVICE_SUCCESS);
         return r;
 }
 
-static int service_can_live_mount(const Unit *u, sd_bus_error *error) {
-        assert(u);
+static int service_can_live_mount(Unit *u, sd_bus_error *error) {
+        Service *s = ASSERT_PTR(SERVICE(u));
 
         /* Ensure that the unit runs in a private mount namespace */
-        if (!exec_needs_mount_namespace(unit_get_exec_context(u), /* params= */ NULL, unit_get_exec_runtime(u)))
+        if (!exec_needs_mount_namespace(&s->exec_context, /* params= */ NULL, s->exec_runtime))
                 return sd_bus_error_setf(
                                 error,
                                 SD_BUS_ERROR_INVALID_ARGS,
diff --git a/src/core/service.h b/src/core/service.h
index 74b2b1c55e..68be9075c1 100644
--- a/src/core/service.h
+++ b/src/core/service.h
@@ -193,8 +193,8 @@ struct Service {
         /* If we shut down, remember why */
         ServiceResult result;
         ServiceResult reload_result;
-        ServiceResult clean_result;
         ServiceResult live_mount_result;
+        ServiceResult clean_result;
 
         bool main_pid_known:1;
         bool main_pid_alien:1;
diff --git a/src/core/unit.c b/src/core/unit.c
index 64ce5967f4..dda98bb861 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -2043,7 +2043,11 @@ int unit_reload(Unit *u) {
                 return -EBADR;
 
         state = unit_active_state(u);
-        if (state == UNIT_RELOADING)
+        if (IN_SET(state, UNIT_RELOADING, UNIT_REFRESHING))
+                /* "refreshing" means some resources in the unit namespace is being updated. Unlike reload,
+                 * the unit processes aren't made aware of refresh. Let's put the job back to queue
+                 * in both cases, as refresh typically takes place before reload and it's better to wait
+                 * for it rather than failing. */
                 return -EAGAIN;
 
         if (state != UNIT_ACTIVE)
@@ -6392,22 +6396,21 @@ Condition *unit_find_failed_condition(Unit *u) {
         return failed_trigger && !has_succeeded_trigger ? failed_trigger : NULL;
 }
 
-int unit_can_live_mount(const Unit *u, sd_bus_error *error) {
+int unit_can_live_mount(Unit *u, sd_bus_error *error) {
         assert(u);
 
         if (!UNIT_VTABLE(u)->live_mount)
                 return sd_bus_error_setf(
                                 error,
-                                SD_BUS_ERROR_INVALID_ARGS,
-                                "Live mounting not supported for unit type '%s' of unit '%s'.",
-                                unit_type_to_string(u->type),
-                                u->id);
+                                SD_BUS_ERROR_NOT_SUPPORTED,
+                                "Live mounting not supported by unit type '%s'",
+                                unit_type_to_string(u->type));
 
         if (u->load_state != UNIT_LOADED)
                 return sd_bus_error_setf(
                                 error,
                                 BUS_ERROR_NO_SUCH_UNIT,
-                                "Unit '%s' not loaded, cannot live mount.",
+                                "Unit '%s' not loaded, cannot live mount",
                                 u->id);
 
         if (!UNIT_VTABLE(u)->can_live_mount)
@@ -6429,7 +6432,7 @@ int unit_live_mount(
         assert(UNIT_VTABLE(u)->live_mount);
 
         if (!UNIT_IS_ACTIVE_OR_RELOADING(unit_active_state(u))) {
-                log_unit_debug(u, "Unit not active");
+                log_unit_debug(u, "Unit not active, cannot perform live mount.");
                 return sd_bus_error_setf(
                                 error,
                                 BUS_ERROR_UNIT_INACTIVE,
@@ -6440,7 +6443,7 @@ int unit_live_mount(
         }
 
         if (unit_active_state(u) == UNIT_REFRESHING) {
-                log_unit_debug(u, "Unit already live mounting");
+                log_unit_debug(u, "Unit already live mounting, refusing further requests.");
                 return sd_bus_error_setf(
                                 error,
                                 BUS_ERROR_UNIT_BUSY,
diff --git a/src/core/unit.h b/src/core/unit.h
index 5ffd82b67e..01e1adf961 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -587,7 +587,7 @@ typedef struct UnitVTable {
 
         /* Add a bind/image mount into the unit namespace while it is running. */
         int (*live_mount)(Unit *u, const char *src, const char *dst, sd_bus_message *message, MountInNamespaceFlags flags, const MountOptions *options, sd_bus_error *error);
-        int (*can_live_mount)(const Unit *u, sd_bus_error *error);
+        int (*can_live_mount)(Unit *u, sd_bus_error *error);
 
         /* Serialize state and file descriptors that should be carried over into the new
          * instance after reexecution. */
@@ -650,7 +650,7 @@ typedef struct UnitVTable {
         int (*bus_commit_properties)(Unit *u);
 
         /* Return the unit this unit is following */
-        Unit *(*following)(Unit *u);
+        Unit* (*following)(Unit *u);
 
         /* Return the set of units that are following each other */
         int (*following_set)(Unit *u, Set **s);
@@ -1047,7 +1047,7 @@ void unit_next_freezer_state(Unit *u, FreezerAction action, FreezerState *ret_ne
 void unit_set_freezer_state(Unit *u, FreezerState state);
 void unit_freezer_complete(Unit *u, FreezerState kernel_state);
 
-int unit_can_live_mount(const Unit *u, sd_bus_error *error);
+int unit_can_live_mount(Unit *u, sd_bus_error *error);
 int unit_live_mount(Unit *u, const char *src, const char *dst, sd_bus_message *message, MountInNamespaceFlags flags, const MountOptions *options, sd_bus_error *error);
 
 Condition *unit_find_failed_condition(Unit *u);
diff --git a/src/shared/bus-util.c b/src/shared/bus-util.c
index ce94597955..ff80e580fc 100644
--- a/src/shared/bus-util.c
+++ b/src/shared/bus-util.c
@@ -439,6 +439,7 @@ int bus_connect_transport(
                                 /* Print a friendly message when the local system is actually not running systemd as PID 1. */
                                 return log_error_errno(SYNTHETIC_ERRNO(EHOSTDOWN),
                                                        "System has not been booted with systemd as init system (PID 1). Can't operate.");
+
                         r = sd_bus_default_system(&bus);
                         break;
 
@@ -515,8 +516,10 @@ int bus_connect_transport_systemd(
                          * private manager bus. To keep compat with existing code that was setting
                          * DBUS_SESSION_BUS_ADDRESS without setting XDG_RUNTIME_DIR, connect to the user
                          * session bus if DBUS_SESSION_BUS_ADDRESS is set and XDG_RUNTIME_DIR isn't. */
-                        if (r == -ENOMEDIUM && secure_getenv("DBUS_SESSION_BUS_ADDRESS"))
+                        if (r == -ENOMEDIUM && secure_getenv("DBUS_SESSION_BUS_ADDRESS")) {
+                                log_debug_errno(r, "$XDG_RUNTIME_DIR not set, unable to connect to private bus. Falling back to session bus.");
                                 r = sd_bus_default_user(ret_bus);
+                        }
 
                         return r;