udev: introduce io.systemd.Udev varlink interface (#35721)

Replaces #25523.

man/rules/meson.build

@@ -1143,7 +1143,8 @@ manpages = [
   '8',
   ['systemd-udevd',
    'systemd-udevd-control.socket',
-   'systemd-udevd-kernel.socket'],
+   'systemd-udevd-kernel.socket',
+   'systemd-udevd-varlink.socket'],
   ''],
  ['systemd-update-done.service', '8', ['systemd-update-done'], ''],
  ['systemd-update-utmp.service',

man/systemd-udevd.service.xml

@@ -20,6 +20,7 @@
     <refname>systemd-udevd.service</refname>
     <refname>systemd-udevd-control.socket</refname>
     <refname>systemd-udevd-kernel.socket</refname>
+    <refname>systemd-udevd-varlink.socket</refname>
     <refname>systemd-udevd</refname>
     <refpurpose>Device event managing daemon</refpurpose>
   </refnamediv>
@@ -28,6 +29,7 @@
     <para><filename>systemd-udevd.service</filename></para>
     <para><filename>systemd-udevd-control.socket</filename></para>
     <para><filename>systemd-udevd-kernel.socket</filename></para>
+    <para><filename>systemd-udevd-varlink.socket</filename></para>
 
     <cmdsynopsis>
       <command>/usr/lib/systemd/systemd-udevd</command>

man/udevadm.xml

@@ -677,7 +677,7 @@
             Note that <filename>systemd-udevd.service</filename> contains
             <option>Restart=always</option> and so as a result, this option restarts systemd-udevd.
             If you want to stop <filename>systemd-udevd.service</filename>, please use the following:
-            <programlisting>systemctl stop systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udevd.service</programlisting>
+            <programlisting>systemctl stop systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udevd-varlink.socket systemd-udevd.service</programlisting>
             </para>
           </listitem>
         </varlistentry>

src/shared/meson.build

@@ -194,6 +194,7 @@ shared_sources = files(
         'varlink-io.systemd.PCRLock.c',
         'varlink-io.systemd.Resolve.c',
         'varlink-io.systemd.Resolve.Monitor.c',
+        'varlink-io.systemd.Udev.c',
         'varlink-io.systemd.UserDatabase.c',
         'varlink-io.systemd.oom.c',
         'varlink-io.systemd.service.c',

src/shared/varlink-io.systemd.Udev.c

@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "varlink-io.systemd.Udev.h"
+
+static SD_VARLINK_DEFINE_METHOD(
+                SetChildrenMax,
+                SD_VARLINK_FIELD_COMMENT("The maximum number of child processes. When 0 is specified, the maximum is determined based on the system resources."),
+                SD_VARLINK_DEFINE_INPUT(number, SD_VARLINK_INT, 0));
+
+static SD_VARLINK_DEFINE_METHOD(
+                SetEnvironment,
+                SD_VARLINK_FIELD_COMMENT("An array of global udev property assignments. Each string must be in KEY=VALUE style."),
+                SD_VARLINK_DEFINE_INPUT(assignments, SD_VARLINK_STRING, SD_VARLINK_ARRAY));
+
+static SD_VARLINK_DEFINE_METHOD(StartExecQueue);
+
+static SD_VARLINK_DEFINE_METHOD(StopExecQueue);
+
+static SD_VARLINK_DEFINE_METHOD(Exit);
+
+SD_VARLINK_DEFINE_INTERFACE(
+                io_systemd_Udev,
+                "io.systemd.Udev",
+                SD_VARLINK_INTERFACE_COMMENT("An interface for controlling systemd-udevd."),
+                SD_VARLINK_SYMBOL_COMMENT("Sets the maximum number of child processes."),
+                &vl_method_SetChildrenMax,
+                SD_VARLINK_SYMBOL_COMMENT("Sets the global udev properties."),
+                &vl_method_SetEnvironment,
+                SD_VARLINK_SYMBOL_COMMENT("Starts processing of queued events."),
+                &vl_method_StartExecQueue,
+                SD_VARLINK_SYMBOL_COMMENT("Stops processing of queued events."),
+                &vl_method_StopExecQueue,
+                SD_VARLINK_SYMBOL_COMMENT("Terminates systemd-udevd. This exists for backward compatibility. Please consider to use 'systemctl stop systemd-udevd.service'."),
+                &vl_method_Exit);

src/shared/varlink-io.systemd.Udev.h

@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include "sd-varlink.h"
+#include "sd-varlink-idl.h"
+
+extern const sd_varlink_interface vl_interface_io_systemd_Udev;

src/test/test-varlink-idl.c

@@ -25,6 +25,7 @@
 #include "varlink-io.systemd.PCRLock.h"
 #include "varlink-io.systemd.Resolve.h"
 #include "varlink-io.systemd.Resolve.Monitor.h"
+#include "varlink-io.systemd.Udev.h"
 #include "varlink-io.systemd.UserDatabase.h"
 #include "varlink-io.systemd.oom.h"
 #include "varlink-io.systemd.service.h"
@@ -197,6 +198,8 @@ TEST(parse_format) {
         print_separator();
         test_parse_format_one(&vl_interface_io_systemd_AskPassword);
         print_separator();
+        test_parse_format_one(&vl_interface_io_systemd_Udev);
+        print_separator();
         test_parse_format_one(&vl_interface_xyz_test);
 }
 

src/udev/meson.build

@@ -37,6 +37,7 @@ libudevd_core_sources = files(
         'udev-node.c',
         'udev-rules.c',
         'udev-spawn.c',
+        'udev-varlink.c',
         'udev-watch.c',
         'udev-worker.c',
 )

src/udev/udev-manager.c

@@ -32,6 +32,7 @@
 #include "udev-spawn.h"
 #include "udev-trace.h"
 #include "udev-util.h"
+#include "udev-varlink.h"
 #include "udev-watch.h"
 #include "udev-worker.h"
 
@@ -148,6 +149,7 @@ Manager* manager_free(Manager *manager) {
 
         sd_device_monitor_unref(manager->monitor);
         udev_ctrl_unref(manager->ctrl);
+        sd_varlink_server_unref(manager->varlink_server);
 
         sd_event_source_unref(manager->inotify_event);
         sd_event_source_unref(manager->kill_workers_event);
@@ -213,7 +215,7 @@ void manager_kill_workers(Manager *manager, bool force) {
         }
 }
 
-static void manager_exit(Manager *manager) {
+void manager_exit(Manager *manager) {
         assert(manager);
 
         manager->exit = true;
@@ -222,7 +224,7 @@ static void manager_exit(Manager *manager) {
 
         /* close sources of new events and discard buffered events */
         manager->ctrl = udev_ctrl_unref(manager->ctrl);
-
+        manager->varlink_server = sd_varlink_server_unref(manager->varlink_server);
         manager->inotify_event = sd_event_source_disable_unref(manager->inotify_event);
         manager->inotify_fd = safe_close(manager->inotify_fd);
 
@@ -246,7 +248,7 @@ void notify_ready(Manager *manager) {
 }
 
 /* reload requested, HUP signal received, rules changed, builtin changed */
-static void manager_reload(Manager *manager, bool force) {
+void manager_reload(Manager *manager, bool force) {
         _cleanup_(udev_rules_freep) UdevRules *rules = NULL;
         usec_t now_usec;
         int r;
@@ -1150,6 +1152,9 @@ static int listen_fds(int *ret_ctrl, int *ret_netlink) {
         for (int i = 0; i < n; i++) {
                 int fd = SD_LISTEN_FDS_START + i;
 
+                if (streq(names[i], "varlink"))
+                        continue; /* The fd will be handled by sd_varlink_server_listen_auto(). */
+
                 if (sd_is_socket(fd, AF_UNIX, SOCK_SEQPACKET, -1) > 0) {
                         if (ctrl_fd >= 0) {
                                 log_debug("Received multiple seqpacket socket (%s), ignoring.", names[i]);
@@ -1417,6 +1422,10 @@ int manager_main(Manager *manager) {
         if (r < 0)
                 return r;
 
+        r = manager_start_varlink_server(manager);
+        if (r < 0)
+                return r;
+
         r = manager_start_device_monitor(manager);
         if (r < 0)
                 return r;

src/udev/udev-manager.h

@@ -5,6 +5,7 @@
 
 #include "sd-device.h"
 #include "sd-event.h"
+#include "sd-varlink.h"
 
 #include "hashmap.h"
 #include "macro.h"
@@ -28,6 +29,7 @@ typedef struct Manager {
 
         sd_device_monitor *monitor;
         UdevCtrl *ctrl;
+        sd_varlink_server *varlink_server;
         int worker_notify_fd;
 
         /* used by udev-watch */
@@ -54,6 +56,8 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(Manager*, manager_free);
 
 int manager_init(Manager *manager);
 int manager_main(Manager *manager);
+void manager_reload(Manager *manager, bool force);
+void manager_exit(Manager *manager);
 
 void notify_ready(Manager *manager);
 

src/udev/udev-varlink.c

@@ -0,0 +1,185 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "json-util.h"
+#include "strv.h"
+#include "udev-manager.h"
+#include "udev-varlink.h"
+#include "varlink-io.systemd.Udev.h"
+#include "varlink-io.systemd.service.h"
+#include "varlink-util.h"
+
+#define UDEV_VARLINK_ADDRESS "/run/udev/io.systemd.Udev"
+
+static int vl_method_reload(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
+        assert(link);
+
+        if (sd_json_variant_elements(parameters) > 0)
+                return sd_varlink_error_invalid_parameter(link, parameters);
+
+        log_debug("Received io.systemd.service.Reload()");
+        manager_reload(userdata, /* force = */ true);
+        return sd_varlink_reply(link, NULL);
+}
+
+static int vl_method_set_log_level(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
+        int r, level;
+
+        static const sd_json_dispatch_field dispatch_table[] = {
+                { "level", _SD_JSON_VARIANT_TYPE_INVALID, json_dispatch_log_level, 0, SD_JSON_MANDATORY },
+                {}
+        };
+
+        assert(link);
+
+        r = sd_varlink_dispatch(link, parameters, dispatch_table, &level);
+        if (r != 0)
+                return r;
+
+        log_debug("Received io.systemd.service.SetLogLevel(%i)", level);
+        manager_set_log_level(userdata, level);
+        return sd_varlink_reply(link, NULL);
+}
+
+static int vl_method_set_children_max(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
+        unsigned n;
+        int r;
+
+        static const sd_json_dispatch_field dispatch_table[] = {
+                { "number", _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_uint, 0, SD_JSON_MANDATORY },
+                {}
+        };
+
+        assert(link);
+
+        r = sd_varlink_dispatch(link, parameters, dispatch_table, &n);
+        if (r != 0)
+                return r;
+
+        log_debug("Received io.systemd.Udev.SetChildrenMax(%u)", n);
+        manager_set_children_max(userdata, n);
+        return sd_varlink_reply(link, NULL);
+}
+
+static int vl_method_set_environment(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
+        int r;
+
+        static const sd_json_dispatch_field dispatch_table[] = {
+                { "assignments", SD_JSON_VARIANT_ARRAY, json_dispatch_strv_environment, 0, SD_JSON_MANDATORY },
+                {}
+        };
+
+        assert(link);
+
+        _cleanup_strv_free_ char **v = NULL;
+        r = sd_varlink_dispatch(link, parameters, dispatch_table, &v);
+        if (r != 0)
+                return r;
+
+        log_debug("Received io.systemd.Udev.SetEnvironment()");
+        manager_set_environment(userdata, v);
+        return sd_varlink_reply(link, NULL);
+}
+
+static int vl_method_start_stop_exec_queue(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
+        Manager *manager = ASSERT_PTR(userdata);
+        const char *method;
+        int r;
+
+        assert(link);
+
+        if (sd_json_variant_elements(parameters) > 0)
+                return sd_varlink_error_invalid_parameter(link, parameters);
+
+        r = sd_varlink_get_current_method(link, &method);
+        if (r < 0)
+                return r;
+
+        log_debug("Received %s()", method);
+        manager->stop_exec_queue = streq(method, "io.systemd.Udev.StopExecQueue");
+        return sd_varlink_reply(link, NULL);
+}
+
+static int vl_method_exit(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
+        assert(link);
+
+        if (sd_json_variant_elements(parameters) > 0)
+                return sd_varlink_error_invalid_parameter(link, parameters);
+
+        /* Refuse further connections. */
+        _unused_ _cleanup_(sd_varlink_flush_close_unrefp) sd_varlink *v = sd_varlink_ref(link);
+
+        log_debug("Received io.systemd.udev.Exit()");
+        manager_exit(userdata);
+        return sd_varlink_reply(link, NULL);
+}
+
+int manager_start_varlink_server(Manager *manager) {
+        _cleanup_(sd_varlink_server_unrefp) sd_varlink_server *v = NULL;
+        int r;
+
+        assert(manager);
+        assert(manager->event);
+
+        r = varlink_server_new(&v, SD_VARLINK_SERVER_ROOT_ONLY | SD_VARLINK_SERVER_INHERIT_USERDATA, manager);
+        if (r < 0)
+                return log_error_errno(r, "Failed to allocate Varlink server: %m");
+
+        /* This needs to be after the inotify and uevent handling, to make sure that the ping is send back
+         * after fully processing the pending uevents (including the synthetic ones we may create due to
+         * inotify events). */
+        r = sd_varlink_server_attach_event(v, manager->event, SD_EVENT_PRIORITY_IDLE);
+        if (r < 0)
+                return log_error_errno(r, "Failed to attach Varlink connection to event loop: %m");
+
+        r = sd_varlink_server_listen_auto(v);
+        if (r < 0)
+                return log_error_errno(r, "Failed to bind to passed Varlink socket: %m");
+        if (r == 0) {
+                r = sd_varlink_server_listen_address(v, UDEV_VARLINK_ADDRESS, 0600);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to bind to Varlink socket: %m");
+        }
+
+        r = sd_varlink_server_add_interface_many(
+                        v,
+                        &vl_interface_io_systemd_service,
+                        &vl_interface_io_systemd_Udev);
+        if (r < 0)
+                return log_error_errno(r, "Failed to add Varlink interface: %m");
+
+        r = sd_varlink_server_bind_method_many(
+                        v,
+                        "io.systemd.service.Ping",          varlink_method_ping,
+                        "io.systemd.service.Reload",        vl_method_reload,
+                        "io.systemd.service.SetLogLevel",   vl_method_set_log_level,
+                        "io.systemd.Udev.SetChildrenMax",   vl_method_set_children_max,
+                        "io.systemd.Udev.SetEnvironment",   vl_method_set_environment,
+                        "io.systemd.Udev.StartExecQueue",   vl_method_start_stop_exec_queue,
+                        "io.systemd.Udev.StopExecQueue",    vl_method_start_stop_exec_queue,
+                        "io.systemd.Udev.Exit",             vl_method_exit);
+        if (r < 0)
+                return log_error_errno(r, "Failed to bind Varlink methods: %m");
+
+        manager->varlink_server = TAKE_PTR(v);
+        return 0;
+}
+
+int udev_varlink_connect(sd_varlink **ret, usec_t timeout) {
+        _cleanup_(sd_varlink_flush_close_unrefp) sd_varlink *link = NULL;
+        int r;
+
+        assert(ret);
+
+        r = sd_varlink_connect_address(&link, UDEV_VARLINK_ADDRESS);
+        if (r < 0)
+                return r;
+
+        (void) sd_varlink_set_description(link, "udev");
+
+        r = sd_varlink_set_relative_timeout(link, timeout);
+        if (r < 0)
+                return r;
+
+        *ret = TAKE_PTR(link);
+        return 0;
+}

src/udev/udev-varlink.h

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include "sd-varlink.h"
+
+#include "time-util.h"
+
+typedef struct Manager Manager;
+
+int manager_start_varlink_server(Manager *manager);
+int udev_varlink_connect(sd_varlink **ret, usec_t timeout);

src/udev/udevadm-control.c

@@ -9,6 +9,7 @@
 #include <unistd.h>
 
 #include "creds-util.h"
+#include "errno-util.h"
 #include "parse-util.h"
 #include "process-util.h"
 #include "static-destruct.h"
@@ -17,6 +18,8 @@
 #include "time-util.h"
 #include "udevadm.h"
 #include "udev-ctrl.h"
+#include "udev-varlink.h"
+#include "varlink-util.h"
 #include "virt.h"
 
 static char **arg_env = NULL;
@@ -174,7 +177,7 @@ static int parse_argv(int argc, char *argv[]) {
         return 1;
 }
 
-static int send_control_commands(void) {
+static int send_control_commands_via_ctrl(void) {
         _cleanup_(udev_ctrl_unrefp) UdevCtrl *uctrl = NULL;
         int r;
 
@@ -238,6 +241,64 @@ static int send_control_commands(void) {
         return 0;
 }
 
+static int send_control_commands(void) {
+        _cleanup_(sd_varlink_flush_close_unrefp) sd_varlink *link = NULL;
+        int r;
+
+        r = udev_varlink_connect(&link, arg_timeout);
+        if (ERRNO_IS_NEG_DISCONNECT(r) || r == -ENOENT) {
+                log_debug_errno(r, "Failed to connect to udev via varlink, falling back to use legacy control socket, ignoring: %m");
+                return send_control_commands_via_ctrl();
+        }
+        if (r < 0)
+                return log_error_errno(r, "Failed to connect to udev via varlink: %m");
+
+        if (arg_exit)
+                return varlink_call_and_log(link, "io.systemd.Udev.Exit", /* parameters = */ NULL, /* reply = */ NULL);
+
+        if (arg_log_level >= 0) {
+                r = varlink_callbo_and_log(link, "io.systemd.service.SetLogLevel", /* reply = */ NULL,
+                                           SD_JSON_BUILD_PAIR_INTEGER("level", arg_log_level));
+                if (r < 0)
+                        return r;
+        }
+
+        if (arg_start_exec_queue >= 0) {
+                r = varlink_call_and_log(link, arg_start_exec_queue ? "io.systemd.Udev.StartExecQueue" : "io.systemd.Udev.StopExecQueue",
+                                         /* parameters = */ NULL, /* reply = */ NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        if (arg_reload) {
+                r = varlink_call_and_log(link, "io.systemd.service.Reload", /* parameters = */ NULL, /* reply = */ NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        if (!strv_isempty(arg_env)) {
+                r = varlink_callbo_and_log(link, "io.systemd.Udev.SetEnvironment", /* reply = */ NULL,
+                                           SD_JSON_BUILD_PAIR_STRV("assignments", arg_env));
+                if (r < 0)
+                        return r;
+        }
+
+        if (arg_max_children >= 0) {
+                r = varlink_callbo_and_log(link, "io.systemd.Udev.SetChildrenMax", /* reply = */ NULL,
+                                           SD_JSON_BUILD_PAIR_UNSIGNED("number", arg_max_children));
+                if (r < 0)
+                        return r;
+        }
+
+        if (arg_ping) {
+                r = varlink_call_and_log(link, "io.systemd.service.Ping", /* parameters = */ NULL, /* reply = */ NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
 int control_main(int argc, char *argv[], void *userdata) {
         int r;
 

src/udev/udevadm-settle.c

@@ -16,8 +16,8 @@
 #include "path-util.h"
 #include "strv.h"
 #include "time-util.h"
-#include "udev-ctrl.h"
 #include "udev-util.h"
+#include "udevadm-util.h"
 #include "udevadm.h"
 #include "unit-def.h"
 #include "virt.h"
@@ -198,23 +198,9 @@ int settle_main(int argc, char *argv[], void *userdata) {
         (void) emit_deprecation_warning();
 
         if (getuid() == 0) {
-                _cleanup_(udev_ctrl_unrefp) UdevCtrl *uctrl = NULL;
-
-                /* guarantee that the udev daemon isn't pre-processing */
-
-                r = udev_ctrl_new(&uctrl);
-                if (r < 0)
-                        return log_error_errno(r, "Failed to create control socket for udev daemon: %m");
-
-                r = udev_ctrl_send_ping(uctrl);
-                if (r < 0) {
-                        log_debug_errno(r, "Failed to connect to udev daemon, ignoring: %m");
-                        return 0;
-                }
-
-                r = udev_ctrl_wait(uctrl, MAX(5 * USEC_PER_SEC, arg_timeout_usec));
-                if (r < 0)
-                        return log_error_errno(r, "Failed to wait for daemon to reply: %m");
+                r = udev_ping(MAX(5 * USEC_PER_SEC, arg_timeout_usec), /* ignore_connection_failure = */ true);
+                if (r <= 0)
+                        return r;
         } else {
                 /* For non-privileged users, at least check if udevd is running. */
                 if (access("/run/udev/control", F_OK) < 0)

src/udev/udevadm-trigger.c

@@ -21,7 +21,6 @@
 #include "strv.h"
 #include "udevadm.h"
 #include "udevadm-util.h"
-#include "udev-ctrl.h"
 #include "virt.h"
 
 static bool arg_verbose = false;
@@ -498,19 +497,10 @@ int trigger_main(int argc, char *argv[], void *userdata) {
         }
 
         if (ping) {
-                _cleanup_(udev_ctrl_unrefp) UdevCtrl *uctrl = NULL;
-
-                r = udev_ctrl_new(&uctrl);
+                r = udev_ping(ping_timeout_usec, /* ignore_connection_failure = */ false);
                 if (r < 0)
-                        return log_error_errno(r, "Failed to initialize udev control: %m");
-
-                r = udev_ctrl_send_ping(uctrl);
-                if (r < 0)
-                        return log_error_errno(r, "Failed to connect to udev daemon: %m");
-
-                r = udev_ctrl_wait(uctrl, ping_timeout_usec);
-                if (r < 0)
-                        return log_error_errno(r, "Failed to wait for daemon to reply: %m");
+                        return r;
+                assert(r > 0);
         }
 
         for (; optind < argc; optind++) {

src/udev/udevadm-util.c

@@ -7,8 +7,11 @@
 #include "bus-util.h"
 #include "device-private.h"
 #include "path-util.h"
+#include "udev-ctrl.h"
+#include "udev-varlink.h"
 #include "udevadm-util.h"
 #include "unit-name.h"
+#include "varlink-util.h"
 
 static int find_device_from_unit(const char *unit_name, sd_device **ret) {
         _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
@@ -122,3 +125,46 @@ int parse_device_action(const char *str, sd_device_action_t *action) {
         *action = a;
         return 1;
 }
+
+static int udev_ping_via_ctrl(usec_t timeout_usec, bool ignore_connection_failure) {
+        _cleanup_(udev_ctrl_unrefp) UdevCtrl *uctrl = NULL;
+        int r;
+
+        r = udev_ctrl_new(&uctrl);
+        if (r < 0)
+                return log_error_errno(r, "Failed to initialize udev control: %m");
+
+        r = udev_ctrl_send_ping(uctrl);
+        if (r < 0) {
+                bool ignore = ignore_connection_failure && (ERRNO_IS_NEG_DISCONNECT(r) || r == -ENOENT);
+                log_full_errno(ignore ? LOG_DEBUG : LOG_ERR, r,
+                               "Failed to connect to udev daemon%s: %m",
+                               ignore ? ", ignoring" : "");
+                return ignore ? 0 : r;
+        }
+
+        r = udev_ctrl_wait(uctrl, timeout_usec);
+        if (r < 0)
+                return log_error_errno(r, "Failed to wait for daemon to reply: %m");
+
+        return 1; /* received reply */
+}
+
+int udev_ping(usec_t timeout_usec, bool ignore_connection_failure) {
+        _cleanup_(sd_varlink_flush_close_unrefp) sd_varlink *link = NULL;
+        int r;
+
+        r = udev_varlink_connect(&link, timeout_usec);
+        if (ERRNO_IS_NEG_DISCONNECT(r) || r == -ENOENT) {
+                log_debug_errno(r, "Failed to connect to udev via varlink, falling back to use legacy control socket, ignoring: %m");
+                return udev_ping_via_ctrl(timeout_usec, ignore_connection_failure);
+        }
+        if (r < 0)
+                return log_error_errno(r, "Failed to connect to udev via varlink: %m");
+
+        r = varlink_call_and_log(link, "io.systemd.service.Ping", /* parameters = */ NULL, /* reply = */ NULL);
+        if (r < 0)
+                return r;
+
+        return 1; /* received reply */
+}

src/udev/udevadm-util.h

@@ -6,3 +6,4 @@
 int find_device(const char *id, const char *prefix, sd_device **ret);
 int find_device_with_action(const char *id, sd_device_action_t action, sd_device **ret);
 int parse_device_action(const char *str, sd_device_action_t *action);
+int udev_ping(usec_t timeout, bool ignore_connection_failure);

test/units/TEST-17-UDEV.10.sh

@@ -28,9 +28,15 @@ blk="$(mktemp)"
 dd if=/dev/zero of="$blk" bs=1M count=1
 loopdev="$(losetup --show -f "$blk")"
 
+# Wait for devices created in the above being processed.
+udevadm settle --timeout 30
+
 udevadm -h
 
+INVOCATION_ID=$(systemctl show --property InvocationID --value systemd-udevd.service)
 udevadm control -e
+# Wait for systemd-udevd.service being restarted.
+timeout 30 bash -ec "while [[ \"\$(systemctl show --property InvocationID --value systemd-udevd.service)\" == \"$INVOCATION_ID\" ]]; do sleep .5; done"
 udevadm control -l emerg
 udevadm control -l alert
 udevadm control -l crit

units/initrd-udevadm-cleanup-db.service

@@ -11,8 +11,8 @@
 Description=Cleanup udev Database
 DefaultDependencies=no
 AssertPathExists=/etc/initrd-release
-Conflicts=systemd-udevd.service systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udev-trigger.service systemd-udev-settle.service
-After=systemd-udevd.service systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udev-trigger.service systemd-udev-settle.service
+Conflicts=systemd-udevd.service systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udevd-varlink.socket systemd-udev-trigger.service systemd-udev-settle.service
+After=systemd-udevd.service systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udevd-varlink.socket systemd-udev-trigger.service systemd-udev-settle.service
 Before=initrd-switch-root.target
 
 [Service]

units/meson.build

@@ -732,6 +732,10 @@ units = [
           'file' : 'systemd-udevd-kernel.socket',
           'symlinks' : ['sockets.target.wants/'],
         },
+        {
+          'file' : 'systemd-udevd-varlink.socket',
+          'symlinks' : ['sockets.target.wants/'],
+        },
         {
           'file' : 'systemd-udevd.service.in',
           'symlinks' : ['sysinit.target.wants/'],

units/systemd-udev-trigger.service

@@ -12,7 +12,7 @@ Description=Coldplug All udev Devices
 Documentation=man:udev(7) man:systemd-udevd.service(8)
 DefaultDependencies=no
 Wants=systemd-udevd.service
-After=systemd-udevd-kernel.socket systemd-udevd-control.socket
+After=systemd-udevd-kernel.socket systemd-udevd-control.socket systemd-udevd-varlink.socket
 Before=sysinit.target
 ConditionPathIsReadWrite=/sys
 

units/systemd-udevd-varlink.socket

@@ -0,0 +1,22 @@
+#  SPDX-License-Identifier: LGPL-2.1-or-later
+#
+#  This file is part of systemd.
+#
+#  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.
+
+[Unit]
+Description=udev Varlink Socket
+Documentation=man:systemd-udevd-varlink.socket(8) man:udev(7)
+DefaultDependencies=no
+Before=sockets.target
+ConditionPathIsReadWrite=/sys
+
+[Socket]
+Service=systemd-udevd.service
+ListenStream=/run/udev/io.systemd.Udev
+FileDescriptorName=varlink
+SocketMode=0600
+RemoveOnStop=yes

units/systemd-udevd.service.in

@@ -23,7 +23,7 @@ DelegateSubgroup=udev
 Type=notify-reload
 # Note that udev will reset the value internally for its workers
 OOMScoreAdjust=-1000
-Sockets=systemd-udevd-control.socket systemd-udevd-kernel.socket
+Sockets=systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udevd-varlink.socket
 Restart=always
 RestartSec=0
 ExecStart={{LIBEXECDIR}}/systemd-udevd