Fix GCC 9.2.1 -Wstringop-truncation

dict_table_rename_in_cache(): Use strcpy() instead of strncpy(),
because they are known to be equivalent in this case (the length
of old_name was already validated).

mariabackup: Invoke strncpy() with one less than the buffer size,
and explicitly add NUL as the last byte of the buffer.

extra/mariabackup/backup_copy.cc

@@ -467,7 +467,7 @@ struct datafile_cur_t {
 	{
 		memset(rel_path, 0, sizeof rel_path);
 		if (filename) {
-			strncpy(abs_path, filename, sizeof abs_path);
+			strncpy(abs_path, filename, sizeof abs_path - 1);
 			abs_path[(sizeof abs_path) - 1] = 0;
 		} else {
 			abs_path[0] = '\0';

extra/mariabackup/changed_page_bitmap.cc

@@ -390,7 +390,7 @@ log_online_setup_bitmap_file_range(
 
 			bitmap_files->files[array_pos].seq_num = file_seq_num;
 			strncpy(bitmap_files->files[array_pos].name,
-				bitmap_dir_file_info.name, FN_REFLEN);
+				bitmap_dir_file_info.name, FN_REFLEN - 1);
 			bitmap_files->files[array_pos].name[FN_REFLEN - 1]
 				= '\0';
 			bitmap_files->files[array_pos].start_lsn

extra/mariabackup/xtrabackup.cc

@@ -2425,7 +2425,8 @@ xtrabackup_copy_datafile(fil_node_t* node, uint thread_n)
 		goto error;
 	}
 
-	strncpy(dst_name, cursor.rel_path, sizeof(dst_name));
+	strncpy(dst_name, cursor.rel_path, sizeof dst_name - 1);
+	dst_name[sizeof dst_name - 1] = '\0';
 
 	/* Setup the page write filter */
 	if (xtrabackup_incremental) {

storage/innobase/dict/dict0dict.cc

@@ -1850,8 +1850,7 @@ dict_table_rename_in_cache(
 			/* The old table name in my_charset_filename is stored
 			in old_name_cs_filename */
 
-			strncpy(old_name_cs_filename, old_name,
-				MAX_FULL_NAME_LEN);
+			strcpy(old_name_cs_filename, old_name);
 			old_name_cs_filename[MAX_FULL_NAME_LEN] = '\0';
 			if (strstr(old_name, TEMP_TABLE_PATH_PREFIX) == NULL) {
 
@@ -1873,8 +1872,7 @@ dict_table_rename_in_cache(
 				} else {
 					/* Old name already in
 					my_charset_filename */
-					strncpy(old_name_cs_filename, old_name,
-						MAX_FULL_NAME_LEN);
+					strcpy(old_name_cs_filename, old_name);
 					old_name_cs_filename[MAX_FULL_NAME_LEN]
 						= '\0';
 				}

storage/xtradb/dict/dict0dict.cc

@@ -1856,8 +1856,7 @@ dict_table_rename_in_cache(
 			/* The old table name in my_charset_filename is stored
 			in old_name_cs_filename */
 
-			strncpy(old_name_cs_filename, old_name,
-				MAX_FULL_NAME_LEN);
+			strcpy(old_name_cs_filename, old_name);
 			old_name_cs_filename[MAX_FULL_NAME_LEN] = '\0';
 			if (strstr(old_name, TEMP_TABLE_PATH_PREFIX) == NULL) {
 
@@ -1879,8 +1878,7 @@ dict_table_rename_in_cache(
 				} else {
 					/* Old name already in
 					my_charset_filename */
-					strncpy(old_name_cs_filename, old_name,
-						MAX_FULL_NAME_LEN);
+					strcpy(old_name_cs_filename, old_name);
 					old_name_cs_filename[MAX_FULL_NAME_LEN]
 						= '\0';
 				}