udev: support reloading udev.conf (#35458)

This makes systemd-udevd reload udev.conf when explicitly requested by
e.g. `udevadm control --reload`.

src/udev/udev-builtin.c

@@ -42,11 +42,28 @@ void udev_builtin_exit(void) {
                         (*b)->exit();
 }
 
-bool udev_builtin_should_reload(void) {
+UdevReloadFlags udev_builtin_should_reload(void) {
+        UdevReloadFlags flags = 0;
+
         for (UdevBuiltinCommand i = 0; i < _UDEV_BUILTIN_MAX; i++)
                 if (builtins[i] && builtins[i]->should_reload && builtins[i]->should_reload())
-                        return true;
+                        flags |= 1u << i;
-        return false;
+
+        if (flags != 0)
+                flags |= UDEV_RELOAD_KILL_WORKERS;
+
+        return flags;
+}
+
+void udev_builtin_reload(UdevReloadFlags flags) {
+        for (UdevBuiltinCommand i = 0; i < _UDEV_BUILTIN_MAX; i++) {
+                if (!FLAGS_SET(flags, 1u << i) || !builtins[i])
+                        continue;
+                if (builtins[i]->exit)
+                        builtins[i]->exit();
+                if (builtins[i]->init)
+                        builtins[i]->init();
+        }
 }
 
 void udev_builtin_list(void) {

src/udev/udev-builtin.h

@@ -59,7 +59,8 @@ const char* udev_builtin_name(UdevBuiltinCommand cmd);
 bool udev_builtin_run_once(UdevBuiltinCommand cmd);
 int udev_builtin_run(UdevEvent *event, UdevBuiltinCommand cmd, const char *command);
 void udev_builtin_list(void);
-bool udev_builtin_should_reload(void);
+UdevReloadFlags udev_builtin_should_reload(void);
+void udev_builtin_reload(UdevReloadFlags flags);
 int udev_builtin_add_property(UdevEvent *event, const char *key, const char *val);
 int udev_builtin_add_propertyf(UdevEvent *event, const char *key, const char *valf, ...) _printf_(3, 4);
 int udev_builtin_import_property(UdevEvent *event, const char *key);

src/udev/udev-config.c

@@ -339,3 +339,27 @@ int manager_load(Manager *manager, int argc, char *argv[]) {
         manager_adjust_config(&manager->config);
         return 1;
 }
+
+UdevReloadFlags manager_reload_config(Manager *manager) {
+        assert(manager);
+
+        UdevConfig old = manager->config;
+
+        manager->config_by_udev_conf = UDEV_CONFIG_INIT;
+        manager_parse_udev_config(&manager->config_by_udev_conf);
+        manager_merge_config(manager);
+        log_set_max_level(manager->config.log_level);
+        manager_adjust_config(&manager->config);
+
+        if (manager->config.resolve_name_timing != old.resolve_name_timing)
+                return UDEV_RELOAD_RULES | UDEV_RELOAD_KILL_WORKERS;
+
+        if (manager->config.log_level != old.log_level ||
+            manager->config.exec_delay_usec != old.exec_delay_usec ||
+            manager->config.timeout_usec != old.timeout_usec ||
+            manager->config.timeout_signal != old.timeout_signal ||
+            manager->config.blockdev_read_only != old.blockdev_read_only)
+                return UDEV_RELOAD_KILL_WORKERS;
+
+        return 0;
+}

src/udev/udev-config.h

@@ -27,4 +27,5 @@ typedef struct UdevConfig {
         }
 
 int manager_load(Manager *manager, int argc, char *argv[]);
+UdevReloadFlags manager_reload_config(Manager *manager);
 void udev_config_set_default_children_max(UdevConfig *c);

src/udev/udev-def.h

@@ -55,3 +55,26 @@ typedef enum UdevBuiltinCommand {
         _UDEV_BUILTIN_MAX,
         _UDEV_BUILTIN_INVALID = -EINVAL,
 } UdevBuiltinCommand;
+
+typedef enum UdevReloadFlags {
+#if HAVE_BLKID
+        UDEV_RELOAD_BUILTIN_BLKID    = 1u << UDEV_BUILTIN_BLKID,
+#endif
+        UDEV_RELOAD_BUILTIN_BTRFS    = 1u << UDEV_BUILTIN_BTRFS,
+        UDEV_RELOAD_BUILTIN_HWDB     = 1u << UDEV_BUILTIN_HWDB,
+        UDEV_RELOAD_BUILTIN_INPUT_ID = 1u << UDEV_BUILTIN_INPUT_ID,
+        UDEV_RELOAD_BUILTIN_KEYBOARD = 1u << UDEV_BUILTIN_KEYBOARD,
+#if HAVE_KMOD
+        UDEV_RELOAD_BUILTIN_KMOD     = 1u << UDEV_BUILTIN_KMOD,
+#endif
+        UDEV_RELOAD_BUILTIN_DRIVER   = 1u << UDEV_BUILTIN_NET_DRIVER,
+        UDEV_RELOAD_BUILTIN_NET_ID   = 1u << UDEV_BUILTIN_NET_ID,
+        UDEV_RELOAD_BUILTIN_NET_LINK = 1u << UDEV_BUILTIN_NET_LINK,
+        UDEV_RELOAD_BUILTIN_PATH_ID  = 1u << UDEV_BUILTIN_PATH_ID,
+        UDEV_RELOAD_BUILTIN_USB_ID   = 1u << UDEV_BUILTIN_USB_ID,
+#if HAVE_ACL
+        UDEV_RELOAD_BUILTIN_UACCESS  = 1u << UDEV_BUILTIN_UACCESS,
+#endif
+        UDEV_RELOAD_KILL_WORKERS     = 1u << (_UDEV_BUILTIN_MAX + 0),
+        UDEV_RELOAD_RULES            = 1u << (_UDEV_BUILTIN_MAX + 1),
+} UdevReloadFlags;

src/udev/udev-manager.c

@@ -262,22 +262,25 @@ static void manager_reload(Manager *manager, bool force) {
         /* Reload SELinux label database, to make the child inherit the up-to-date database. */
         mac_selinux_maybe_reload();
 
-        /* Nothing changed. It is not necessary to reload. */
+        UdevReloadFlags flags = udev_builtin_should_reload();
-        if (!udev_rules_should_reload(manager->rules) && !udev_builtin_should_reload()) {
+        if (udev_rules_should_reload(manager->rules))
-
+                flags |= UDEV_RELOAD_RULES | UDEV_RELOAD_KILL_WORKERS;
-                if (!force)
+        if (flags == 0 && !force)
+                /* Neither .rules files nor config files for builtins e.g. .link files changed. It is not
+                 * necessary to reload configs. Note, udev.conf is not checked in the above, hence reloaded
+                 * when explicitly requested or at least one .rules file or friend is updated. */
                 return;
 
-                /* If we eat this up, then tell our service manager to just continue */
-                (void) notify_reloading_full("Skipping configuration reloading, nothing changed.");
-        } else {
         (void) notify_reloading();
 
+        flags |= manager_reload_config(manager);
+
+        if (FLAGS_SET(flags, UDEV_RELOAD_KILL_WORKERS))
                 manager_kill_workers(manager, false);
 
-                udev_builtin_exit();
+        udev_builtin_reload(flags);
-                udev_builtin_init();
 
+        if (FLAGS_SET(flags, UDEV_RELOAD_RULES)) {
                 r = udev_rules_load(&rules, manager->config.resolve_name_timing);
                 if (r < 0)
                         log_warning_errno(r, "Failed to read udev rules, using the previously loaded rules, ignoring: %m");

test/units/TEST-17-UDEV.03.sh

@@ -27,7 +27,7 @@ event_timeout=10
 timeout_signal=SIGABRT
 EOF
 
-    systemctl restart systemd-udevd.service
+    systemctl reload systemd-udevd.service
 }
 
 # shellcheck disable=SC2317
@@ -40,7 +40,7 @@ teardown() {
 
     rm -rf "$TMPDIR"
     rm -f "$TEST_RULE" "$TEST_CONF"
-    systemctl restart systemd-udevd.service
+    systemctl reload systemd-udevd.service
 }
 
 run_test_timeout() {

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

@@ -18,7 +18,7 @@ at_exit() {
     # Forcibly kills sleep command invoked by the udev rule before restarting,
     # otherwise systemctl restart below will takes longer.
     killall -KILL sleep
-    systemctl restart systemd-udevd.service
+    udevadm control --reload
     ip link del "$IFNAME"
 }
 
@@ -36,7 +36,7 @@ cat >/run/udev/rules.d/99-testsuite.rules <<EOF
 SUBSYSTEM=="net", ACTION=="change", KERNEL=="${IFNAME}", OPTIONS="log_level=debug", RUN+="/usr/bin/sleep 1000"
 EOF
 
-systemctl restart systemd-udevd.service
+udevadm control --reload
 
 ip link add "$IFNAME" type dummy
 IFINDEX=$(ip -json link show "$IFNAME" | jq '.[].ifindex')