sd-bus: Cite sd_bus_creds_unref in sd_bus_get_name_creds docs

It's not always mounted, e.g. during the build-time tests, it's running inside
a chroot (that's how Debian/Ubuntu build packages, in chroots) so this test
always fails because /sys/fs/cgroup isn't mounted.

.clang-format

@@ -3,10 +3,24 @@
 # result MUST NOT be committed indiscriminately, but each automated
 # change should be reviewed and only the appropriate ones commited.
 #
-# To apply the coding style you can run the following command (assuming you
+# The easiest way to apply the formatting to your changes ONLY,
-# installed clang-format on your system):
+# is to use the git-clang-format script (usually installed with clang-format).
 #
+# -  Fixup formatting before committing
+# 1. Edit and stage your files.
+# 2. Run `git clang-format`.
+# 3. Verify + correct + (un)stage changes.
+# 4. Commit.
+#
+# -  Fixup formatting after committing
+# 1. Commit your changes.
+# 2. Run `git clang-format HEAD~` - Refer the commit *before* your changes here.
+# 3. Verify + correct changes, `git difftool -d` can help here.
+# 4. Stage + commit, potentially with `--amend` (means to fixup the last commit).
+#
+# To run clang-format on all sourcefiles, use the following line:
 # $ git ls-files 'src/*.[ch]' 'src/*.cc' | xargs clang-format -i -style=file
+#
 # You can find more information on the different config parameters in this file here:
 # https://clang.llvm.org/docs/ClangFormatStyleOptions.html
 ---

man/sd_bus_get_name_creds.xml

@@ -54,7 +54,8 @@
     for a list of possible flags. On success, <parameter>creds</parameter> contains a new
     <structname>sd_bus_creds</structname> instance with the requested information. Ownership of this instance
     belongs to the caller and it should be freed once no longer needed by calling
-    <function>sd_bus_creds_unref()</function>.</para>
+    <citerefentry><refentrytitle>sd_bus_creds_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+    </para>
 
     <para><function>sd_bus_get_owner_creds()</function> queries the credentials of the creator of the given
     bus. The <parameter>mask</parameter> and <parameter>creds</parameter> parameters behave the same as in
@@ -113,8 +114,8 @@
 
     <para>
       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
-      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_creds_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     </para>
   </refsect1>
-
 </refentry>

src/basic/cgroup-util.c

@@ -2010,6 +2010,9 @@ int cg_unified_cached(bool flush) {
                                 unified_cache = CGROUP_UNIFIED_NONE;
                         }
                 }
+        } else if (F_TYPE_EQUAL(fs.f_type, SYSFS_MAGIC)) {
+                return log_debug_errno(SYNTHETIC_ERRNO(ENOMEDIUM),
+                                       "No filesystem is currently mounted on /sys/fs/cgroup.");
         } else
                 return log_debug_errno(SYNTHETIC_ERRNO(ENOMEDIUM),
                                        "Unknown filesystem type %llx mounted on /sys/fs/cgroup.",

src/test/test-cgroup.c

@@ -44,6 +44,13 @@ static void test_cg_split_spec(void) {
 
 static void test_cg_create(void) {
         log_info("/* %s */", __func__);
+        int r;
+
+        r = cg_unified_cached(false);
+        if (r < 0) {
+                log_info_errno(r, "Skipping %s: %m", __func__);
+                return;
+        }
 
         _cleanup_free_ char *here = NULL;
         assert_se(cg_pid_get_path_shifted(0, NULL, &here) >= 0);
@@ -53,7 +60,6 @@ static void test_cg_create(void) {
                    *test_c = prefix_roota(here, "/test-b/test-c"),
                    *test_d = prefix_roota(here, "/test-b/test-d");
         char *path;
-        int r;
 
         log_info("Paths for test:\n%s\n%s", test_a, test_b);