MDEV-21933 INFORMATION_SCHEMA.INNODB_SYS_TABLESPACES accesses SYS_DATAFILES

All tablespace metadata is buffered in fil_system. There is a LRU
mechanism, but that only controls the opening and closing of
fil_node_t::handle.

It is much more efficient and less error-prone to access data file names
by looking up the fil_space_t object rather than by essentially joining
each row with an access to SYS_DATAFILES via the InnoDB internal SQL parser.

dict_get_first_path(): Declare static. The function may only be needed
when loading or updating the data dictionary. Also, change a condition
in order to avoid a bogus GCC 10 -Wstringop-overflow warning for
mem_strdupl() about len==ULINT_UNDEFINED.

i_s_sys_tablespaces_fill_table(): Do not access other InnoDB internal
dictionary tables than SYS_TABLESPACES.

storage/innobase/dict/dict0load.cc

 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2016, 2019, MariaDB Corporation.
+Copyright (c) 2016, 2020, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -805,7 +805,7 @@ dict_process_sys_datafiles(
 @param[in]	space_id	Tablespace ID
 @return First filepath (caller must invoke ut_free() on it)
 @retval NULL if no SYS_DATAFILES entry was found. */
-char*
+static char*
 dict_get_first_path(
 	ulint	space_id)
 {
@@ -863,7 +863,7 @@ dict_get_first_path(
 			ut_ad(len > 0);
 			ut_ad(len < OS_FILE_MAX_PATH);
 
-			if (len > 0 && len != UNIV_SQL_NULL) {
+			if (len > 0 && len < UNIV_SQL_NULL) {
 				filepath = mem_strdupl(
 					reinterpret_cast<const char*>(field),
 					len);

storage/innobase/handler/i_s.cc

@@ -8057,31 +8057,24 @@ i_s_dict_fill_sys_tablespaces(
 	OK(fields[SYS_TABLESPACES_ZIP_PAGE_SIZE]->store(
 		   page_size.physical(), true));
 
-	char*	filepath = NULL;
-	if (FSP_FLAGS_HAS_DATA_DIR(cflags)) {
-		mutex_enter(&dict_sys->mutex);
-		filepath = dict_get_first_path(space);
-		mutex_exit(&dict_sys->mutex);
-	}
-
-	if (filepath == NULL) {
-		filepath = fil_make_filepath(NULL, name, IBD, false);
-	}
-
 	os_file_stat_t	stat;
 	os_file_size_t	file;
 
 	memset(&file, 0xff, sizeof(file));
 	memset(&stat, 0x0, sizeof(stat));
 
-	if (filepath != NULL) {
+	if (fil_space_t* s = fil_space_acquire_silent(space)) {
+		const char *filepath = s->chain.start
+			? s->chain.start->name : NULL;
+		if (!filepath) {
+			goto file_done;
+		}
 
 		file = os_file_get_size(filepath);
 
 		/* Get the file system (or Volume) block size. */
-		dberr_t	err = os_file_get_status(filepath, &stat, false, false);
-
-		switch(err) {
+		switch (dberr_t err = os_file_get_status(filepath, &stat,
+							 false, false)) {
 		case DB_FAIL:
 			ib::warn()
 				<< "File '" << filepath << "', failed to get "
@@ -8099,7 +8092,8 @@ i_s_dict_fill_sys_tablespaces(
 			break;
 		}
 
-		ut_free(filepath);
+file_done:
+		fil_space_release(s);
 	}
 
 	if (file.m_total_size == static_cast<os_offset_t>(~0)) {

storage/innobase/include/dict0load.h

 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2019, MariaDB Corporation.
+Copyright (c) 2017, 2020, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -88,14 +88,6 @@ dict_get_first_table_name_in_db(
 /*============================*/
 	const char*	name);	/*!< in: database name which ends to '/' */
 
-/** Get the first filepath from SYS_DATAFILES for a given space_id.
-@param[in]	space_id	Tablespace ID
-@return First filepath (caller must invoke ut_free() on it)
-@retval NULL if no SYS_DATAFILES entry was found. */
-char*
-dict_get_first_path(
-	ulint	space_id);
-
 /** Make sure the data_file_name is saved in dict_table_t if needed.
 Try to read it from the fil_system first, then from SYS_DATAFILES.
 @param[in]	table		Table object