bus: do kdbus only if this is enabled on the configure switch

Since we want to retain the ability to break kernel ←→ userspace ABI
after the next release, let's not make use by default of kdbus, so that
people with future kernels will not suddenly break with current systemd
versions.

kdbus support is left in all builds but must now be explicitly requested
at runtime (for example via setting $DBUS_SESSION_BUS). Via a configure
switch the old behaviour can be restored. In fact, we change autogen.sh
to do this, so that git builds (which run autogen.sh) get kdbus by
default, but tarball builds (which ue the configure defaults) do not get
it, and hence this stays out of the distros by default.

TODO

@@ -129,7 +129,7 @@ Features:
   - support "const" properties as flag
   - add API to clone sd_bus_message objects
   - SD_BUS_COMMENT() macro for inclusion in vtables, syntax inspired by gdbus
-  - unelss configure option is specified refuse connecting and creating kdbus, so that we can break compat
+  - make sd_bus_open_system_container() kdbus aware
   - longer term:
     * priority queues
     * priority inheritance

autogen.sh

@@ -54,10 +54,10 @@ args="$args \
 fi
 
 if [ "x$1" = "xc" ]; then
-        ./configure CFLAGS='-g -O0' $args
+        ./configure CFLAGS='-g -O0' --enable-kdbus $args
         make clean
 elif [ "x$1" = "xg" ]; then
-        ./configure CFLAGS='-g -Og' $args
+        ./configure CFLAGS='-g -Og' --enable-kdbus $args
         make clean
 else
         echo
@@ -65,6 +65,6 @@ else
         echo "Initialized build system. For a common configuration please run:"
         echo "----------------------------------------------------------------"
         echo
-        echo "./configure CFLAGS='-g -O0' $args"
+        echo "./configure CFLAGS='-g -O0' --enable-kdbus $args"
         echo
 fi

configure.ac

@@ -799,6 +799,15 @@ if test "x$enable_multi_seat_x" != "xno"; then
 fi
 AM_CONDITIONAL(ENABLE_MULTI_SEAT_X, [test "$have_multi_seat_x" = "yes"])
 
+# ------------------------------------------------------------------------------
+have_kdbus=no
+AC_ARG_ENABLE(kdbus, AS_HELP_STRING([--enable-kdbus], [do not connect to kdbus by default]))
+if test "x$enable_kdbus" == "xyes"; then
+        AC_DEFINE(ENABLE_KDBUS, 1, [Define if kdbus support is to be enabled])
+        have_kdbus=yes
+fi
+AM_CONDITIONAL(ENABLE_KDBUS, [test "$have_kdbus" = "yes"])
+
 # ------------------------------------------------------------------------------
 AC_ARG_WITH(rc-local-script-path-start,
         AS_HELP_STRING([--with-rc-local-script-path-start=PATH],
@@ -1084,6 +1093,7 @@ AC_MSG_RESULT([
         gudev:                   ${enable_gudev}
         gintrospection:          ${enable_introspection}
         multi-seat-x:            ${have_multi_seat_x}
+        kdbus:                   ${have_kdbus}
         Python:                  ${have_python}
         Python Headers:          ${have_python_devel}
         man pages:               ${have_manpages}

src/core/manager.c

@@ -414,6 +414,7 @@ static int manager_setup_kdbus(Manager *m) {
 
         assert(m);
 
+#ifdef ENABLE_KDBUS
         if (m->kdbus_fd >= 0)
                 return 0;
 
@@ -428,6 +429,8 @@ static int manager_setup_kdbus(Manager *m) {
         }
 
         log_info("Successfully set up kdbus on %s", p);
+#endif
+
         return 0;
 }
 

src/libsystemd-bus/sd-bus.c

@@ -993,7 +993,11 @@ _public_ int sd_bus_open_system(sd_bus **ret) {
         if (e)
                 r = sd_bus_set_address(b, e);
         else
+#ifdef ENABLE_KDBUS
                 r = sd_bus_set_address(b, "kernel:path=/dev/kdbus/0-system/bus;unix:path=/run/dbus/system_bus_socket");
+#else
+                r = sd_bus_set_address(b, "unix:path=/run/dbus/system_bus_socket");
+#endif
 
         if (r < 0)
                 goto fail;
@@ -1035,13 +1039,22 @@ _public_ int sd_bus_open_user(sd_bus **ret) {
 
                         ee = bus_address_escape(e);
                         if (!ee) {
-                                r = -ENOENT;
+                                r = -ENOMEM;
                                 goto fail;
                         }
 
+#ifdef ENABLE_KDBUS
                         asprintf(&b->address, "kernel:path=/dev/kdbus/%lu-user/bus;unix:path=%s/bus", (unsigned long) getuid(), ee);
-                } else
+#else
+                        b->address = strjoin("unix:path=", ee, "/bus", NULL);
+#endif
+                } else {
+#ifdef ENABLE_KDBUS
                         asprintf(&b->address, "kernel:path=/dev/kdbus/%lu-user/bus", (unsigned long) getuid());
+#else
+                        return -ECONNREFUSED;
+#endif
+                }
 
                 if (!b->address) {
                         r = -ENOMEM;