systemd-path: add 'system-search-configuration'

This provides functionality to replace what was provided by the preceding
revert:

  $ build/systemd-path system-search-configuration --suffix=sysctl.d
  /etc/sysctl.d:/run/sysctl.d:/usr/local/lib/sysctl.d:/usr/lib/sysctl.d

The result is identical, but more generic, since by changing suffix we can also
get the answer for sysusers.d, tmpfiles.d, and any other of the directories
which follow the same general rule.

man/sd_path_lookup.xml

@@ -41,6 +41,7 @@
         <constant>SD_PATH_SYSTEM_STATE_FACTORY</constant>,
 
         <constant>SD_PATH_SYSTEM_CONFIGURATION</constant>,
+        <constant>SD_PATH_SYSTEM_SEARCH_CONFIGURATION</constant>,
         <constant>SD_PATH_SYSTEM_RUNTIME</constant>,
         <constant>SD_PATH_SYSTEM_RUNTIME_LOGS</constant>,
         <constant>SD_PATH_SYSTEM_STATE_PRIVATE</constant>,

src/libsystemd/sd-path/sd-path.c

@@ -524,6 +524,9 @@ static int get_search(uint64_t type, char ***ret) {
 
         switch (type) {
 
+        case SD_PATH_SYSTEM_SEARCH_CONFIGURATION:
+                return strv_from_nulstr(ret, CONF_PATHS_NULSTR(""));
+
         case SD_PATH_SEARCH_BINARIES:
                 return search_from_environment(ret,
                                                NULL,

src/path/path-tool.c

@@ -22,6 +22,8 @@ static const char* const path_table[_SD_PATH_MAX] = {
         [SD_PATH_TEMPORARY]                                   = "temporary",
         [SD_PATH_TEMPORARY_LARGE]                             = "temporary-large",
 
+        [SD_PATH_SYSTEM_SEARCH_CONFIGURATION]                 = "system-search-configuration",
+
         [SD_PATH_SYSTEM_BINARIES]                             = "system-binaries",
         [SD_PATH_SYSTEM_INCLUDE]                              = "system-include",
         [SD_PATH_SYSTEM_LIBRARY_PRIVATE]                      = "system-library-private",

src/systemd/sd-path.h

@@ -44,6 +44,9 @@ __extension__ enum {
         SD_PATH_SYSTEM_STATE_CACHE,
         SD_PATH_SYSTEM_STATE_SPOOL,
 
+        /* generic system configuration */
+        SD_PATH_SYSTEM_SEARCH_CONFIGURATION,
+
         /* Vendor supplied data */
         SD_PATH_USER_BINARIES,
         SD_PATH_USER_LIBRARY_PRIVATE,

test/units/TEST-74-AUX-UTILS.path.sh

@@ -51,6 +51,8 @@ assert_eq "$(systemd-path --suffix='' system-runtime)" "/run"
 assert_eq "$(systemd-path --suffix='🤔' system-runtime)" "/run/🤔"
 assert_eq "$(systemd-path --suffix=hello system-runtime)" "/run/hello"
 
+assert_eq "$(systemd-path system-search-configuration --suffix=sysctl.d)" "/etc/sysctl.d:/run/sysctl.d:/usr/local/lib/sysctl.d:/usr/lib/sysctl.d"
+
 # Note for the stuff below: everything defaults to $HOME, only the desktop
 # directory defaults to $HOME/Desktop.
 #