core: deprecate %c, %r, %R specifiers

%c and %r rely on settings made in the unit files themselves and hence resolve
to different values depending on whether they are used before or after Slice=.
Let's simply deprecate them and drop them from the documentation, as that's not
really possible to fix. Moreover they are actually redundant, as the same
information may always be queried from /proc/self/cgroup and /proc/1/cgroup.

(Accurately speaking, %R is actually not broken like this as it is constant.
However, let's remove all cgroup-related specifiers at once, as it is also
redundant, and doesn't really make much sense alone.)

2 files changed, 13 insertions, 18 deletions

diff --git a/man/systemd.unit.xml b/man/systemd.unit.xml
index a767b2e80a..dbb0dc7bd7 100644
--- a/man/systemd.unit.xml
+++ b/man/systemd.unit.xml
@@ -1246,21 +1246,6 @@
       <entry>This is either the unescaped instance name (if applicable) with <filename>/</filename> prepended (if applicable), or the unescaped prefix name prepended with <filename>/</filename>.</entry>
           </row>
           <row>
-      <entry><literal>%c</literal></entry>
-      <entry>Control group path of the unit</entry>
-      <entry>This path does not include the <filename>/sys/fs/cgroup/systemd/</filename> prefix.</entry>
-          </row>
-          <row>
-      <entry><literal>%r</literal></entry>
-      <entry>Control group path of the slice the unit is placed in</entry>
-      <entry>This usually maps to the parent control group path of <literal>%c</literal>.</entry>
-          </row>
-          <row>
-      <entry><literal>%R</literal></entry>
-      <entry>Root control group path below which slices and units are placed</entry>
-      <entry>For system instances, this resolves to <filename>/</filename>, except in containers, where this maps to the container's root control group path.</entry>
-          </row>
-          <row>
       <entry><literal>%t</literal></entry>
       <entry>Runtime directory</entry>
       <entry>This is either <filename>/run</filename> (for the system manager) or the path <literal>$XDG_RUNTIME_DIR</literal> resolves to (for user managers).</entry>
diff --git a/src/core/unit-printf.c b/src/core/unit-printf.c
index 4c95127c80..8f7eb84c61 100644
--- a/src/core/unit-printf.c
+++ b/src/core/unit-printf.c
@@ -78,12 +78,18 @@ static int specifier_filename(char specifier, void *data, void *userdata, char *
                 return unit_name_to_path(u->id, ret);
 }
 
+static void bad_specifier(Unit *u, char specifier) {
+        log_unit_warning(u, "Specifier '%%%c' used in unit configuration, which is deprecated. Please update your unit file, as it does not work as intended.", specifier);
+}
+
 static int specifier_cgroup(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
         char *n;
 
         assert(u);
 
+        bad_specifier(u, specifier);
+
         if (u->cgroup_path)
                 n = strdup(u->cgroup_path);
         else
@@ -101,6 +107,8 @@ static int specifier_cgroup_root(char specifier, void *data, void *userdata, cha
 
         assert(u);
 
+        bad_specifier(u, specifier);
+
         n = strdup(u->manager->cgroup_root);
         if (!n)
                 return -ENOMEM;
@@ -115,6 +123,8 @@ static int specifier_cgroup_slice(char specifier, void *data, void *userdata, ch
 
         assert(u);
 
+        bad_specifier(u, specifier);
+
         if (UNIT_ISSET(u->slice)) {
                 Unit *slice;
 
@@ -238,9 +248,9 @@ int unit_full_printf(Unit *u, const char *format, char **ret) {
          * (which are likely not suitable for unescaped inclusion in unit names):
          *
          * %f: the unescaped instance if set, otherwise the id unescaped as path
-         * %c: cgroup path of unit
-         * %r: where units in this slice are placed in the cgroup tree
-         * %R: the root of this systemd's instance tree
+         * %c: cgroup path of unit (deprecated)
+         * %r: where units in this slice are placed in the cgroup tree (deprecated)
+         * %R: the root of this systemd's instance tree (deprecated)
          * %t: the runtime directory to place sockets in (e.g. "/run" or $XDG_RUNTIME_DIR)
          *
          * %h: the homedir of the running user