MDEV-15543: tmpfile.d not for datadir

With the default datadir path of /var/lib/mysql the same
as the path of the unix socket, this tmpfiles.d file
was generated to "create" a datadir. This wasn't intended.

In this case we comment out the entry and explain why.

Add extra ideas on other temporary directories that
may be specified in this file.

support-files/CMakeLists.txt

@@ -212,6 +212,9 @@ IF(UNIX AND NOT WITHOUT_SERVER)
 
   IF((HAVE_SYSTEMD OR INSTALL_SYSTEMD_TMPUSERS) AND INSTALL_SYSTEMD_TMPFILESDIR)
     get_filename_component(MYSQL_UNIX_DIR ${MYSQL_UNIX_ADDR} DIRECTORY)
+    IF(MYSQL_DATADIR STREQUAL MYSQL_UNIX_DIR)
+      SET(DISABLE_TMP "#")
+    ENDIF()
     CONFIGURE_FILE(tmpfiles.conf.in
             ${CMAKE_CURRENT_BINARY_DIR}/tmpfiles.conf @ONLY)
     INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/tmpfiles.conf

support-files/tmpfiles.conf.in

@@ -1 +1,11 @@
-d @MYSQL_UNIX_DIR@ 0755 @MYSQLD_USER@ @MYSQLD_USER@ -
+# This is the directory where the unix socket
+# of MariaDB is created.
+# Other temporary directories can be created here like:
+# * tmpdir
+# * innodb_tmpdir
+# * innodb_temp_data_file_path
+# * rocksdb_tmpdir
+# etc.
+# It shouldn't be used for datadir which is why it
+# may be disabled.
+@DISABLE_TMP@d @MYSQL_UNIX_DIR@ 0755 @MYSQLD_USER@ @MYSQLD_USER@ -