6 files changed, 37 insertions, 8 deletions
diff --git a/src/core/busname.c b/src/core/busname.c
index 1278c96638..3dc6e87e55 100644
--- a/src/core/busname.c
+++ b/src/core/busname.c
@@ -988,7 +988,7 @@ static bool busname_supported(void) {
         static int supported = -1;
 
         if (supported < 0)
-                supported = access("/sys/fs/kdbus", F_OK) >= 0;
+                supported = is_kdbus_available();
 
         return supported;
 }
diff --git a/src/core/kmod-setup.c b/src/core/kmod-setup.c
index c5117b47ee..132c3e866c 100644
--- a/src/core/kmod-setup.c
+++ b/src/core/kmod-setup.c
@@ -28,6 +28,7 @@
 
 #include "macro.h"
 #include "capability.h"
+#include "bus-util.h"
 #include "kmod-setup.h"
 
 #ifdef HAVE_KMOD
@@ -44,10 +45,6 @@ static void systemd_kmod_log(
         log_internalv(LOG_DEBUG, 0, file, line, fn, format, args);
         REENABLE_WARNING;
 }
-
-static bool cmdline_check_kdbus(void) {
-        return get_proc_cmdline_key("kdbus", NULL) > 0;
-}
 #endif
 
 int kmod_setup(void) {
@@ -69,7 +66,7 @@ int kmod_setup(void) {
                 { "unix",      "/proc/net/unix",            true,  NULL                },
 
                 /* IPC is needed before we bring up any other services */
-                { "kdbus",     "/sys/fs/kdbus",             false, cmdline_check_kdbus },
+                { "kdbus",     "/sys/fs/kdbus",             false, is_kdbus_wanted     },
 
                 /* netfilter is needed by networkd, nspawn among others, and cannot be autoloaded */
                 { "ip_tables", "/proc/net/ip_tables_names", false, NULL                },
diff --git a/src/core/manager.c b/src/core/manager.c
index 8c8645b68d..c918f191c9 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -721,6 +721,8 @@ static int manager_setup_kdbus(Manager *m) {
 
         if (m->test_run || m->kdbus_fd >= 0)
                 return 0;
+        if (!is_kdbus_available())
+                return -ESOCKTNOSUPPORT;
 
         if (m->running_as == SYSTEMD_SYSTEM && detect_container(NULL) <= 0)
                 bus_kernel_fix_attach_mask();
diff --git a/src/dbus1-generator/dbus1-generator.c b/src/dbus1-generator/dbus1-generator.c
index c909a4b1da..4980fccc31 100644
--- a/src/dbus1-generator/dbus1-generator.c
+++ b/src/dbus1-generator/dbus1-generator.c
@@ -302,7 +302,7 @@ int main(int argc, char *argv[]) {
 
         umask(0022);
 
-        if (access("/sys/fs/kdbus/control", F_OK) < 0)
+        if (!is_kdbus_available())
                 return 0;
 
         r = cg_pid_get_owner_uid(0, NULL);
@@ -310,7 +310,7 @@ int main(int argc, char *argv[]) {
                 path = "/usr/share/dbus-1/services";
                 type = "session";
                 units = USER_DATA_UNIT_PATH;
-        } else if (r == -ENOENT) {
+        } else if (r == -ENXIO) {
                 path = "/usr/share/dbus-1/system-services";
                 type = "system";
                 units = SYSTEM_DATA_UNIT_PATH;
diff --git a/src/libsystemd/sd-bus/bus-util.c b/src/libsystemd/sd-bus/bus-util.c
index f0695bfde0..7536a96b8d 100644
--- a/src/libsystemd/sd-bus/bus-util.c
+++ b/src/libsystemd/sd-bus/bus-util.c
@@ -2051,3 +2051,30 @@ int bus_path_decode_unique(const char *path, const char *prefix, char **ret_send
         *ret_external = external;
         return 1;
 }
+
+bool is_kdbus_wanted(void) {
+        _cleanup_free_ char *value = NULL;
+        int r;
+
+        if (get_proc_cmdline_key("kdbus", NULL) <= 0) {
+                r = get_proc_cmdline_key("kdbus=", &value);
+                if (r <= 0 || parse_boolean(value) != 1)
+                        return false;
+        }
+
+        return true;
+}
+
+bool is_kdbus_available(void) {
+        _cleanup_close_ int fd = -1;
+        struct kdbus_cmd cmd = { .size = sizeof(cmd), .flags = KDBUS_FLAG_NEGOTIATE };
+
+        if (!is_kdbus_wanted())
+                return false;
+
+        fd = open("/sys/fs/kdbus/control", O_RDWR | O_CLOEXEC | O_NONBLOCK | O_NOCTTY);
+        if (fd < 0)
+                return false;
+
+        return ioctl(fd, KDBUS_CMD_BUS_MAKE, &cmd) >= 0;
+}
diff --git a/src/libsystemd/sd-bus/bus-util.h b/src/libsystemd/sd-bus/bus-util.h
index d3a18e2d94..093b48b8f8 100644
--- a/src/libsystemd/sd-bus/bus-util.h
+++ b/src/libsystemd/sd-bus/bus-util.h
@@ -205,3 +205,6 @@ int bus_deserialize_and_dump_unit_file_changes(sd_bus_message *m, bool quiet);
 
 int bus_path_encode_unique(sd_bus *b, const char *prefix, const char *sender_id, const char *external_id, char **ret_path);
 int bus_path_decode_unique(const char *path, const char *prefix, char **ret_sender, char **ret_external);
+
+bool is_kdbus_wanted(void);
+bool is_kdbus_available(void);