MDEV-6257: MariaDB 5.5 fails to start with 10.0 InnoDB log files

Analysis: Can't disable the error message because you may get database
started with incorrect log file size. 

Fix: Thus only improve the error message to give more information 
to users.

storage/innobase/srv/srv0start.c

@@ -625,16 +625,25 @@ open_or_create_log_file(
 		    || size_high != srv_calc_high32(srv_log_file_size)) {
 
 			/* By default 5.6 based InnoDB will create 48M log
-			file but 5.5 only 5M. Actual size error must be
-			tested later. */
+			file but 5.5 only 5M. Thus give hint to user. */
+ 			fprintf(stderr,
+				"InnoDB: Error: log file %s is"
+ 				" of different size %lu %lu bytes\n"
+ 				"InnoDB: than specified in the .cnf"
+ 				" file %lu %lu bytes!\n",
+ 				name, (ulong) size_high, (ulong) size,
+ 				(ulong) srv_calc_high32(srv_log_file_size),
+ 				(ulong) srv_calc_low32(srv_log_file_size));
+
 			fprintf(stderr,
-				"InnoDB: Warning: log file %s is"
-				" of different size %lu %lu bytes\n"
-				"InnoDB: than specified in the .cnf"
-				" file %lu %lu bytes!\n",
-				name, (ulong) size_high, (ulong) size,
-				(ulong) srv_calc_high32(srv_log_file_size),
-				(ulong) srv_calc_low32(srv_log_file_size));
+				"InnoDB: Possible causes for this error:\n"
+				" (a) Incorrect log file is used or log file size is changed\n"
+				" (b) In case default size is used this log file is from 10.0\n"
+				" (c) Log file is corrupted or there was not enough disk space\n"
+				" In case (b) you need to set innodb_log_file_size = 48M\n");
+
+			return(DB_ERROR);
+
 		}
 	} else {
 		*log_file_created = TRUE;

storage/xtradb/srv/srv0start.c

@@ -619,16 +619,24 @@ open_or_create_log_file(
 		    || size_high != srv_calc_high32(srv_log_file_size)) {
 
 			/* By default 5.6 based InnoDB will create 48M log
-			file but 5.5 only 5M. Actual size error must be
-			tested later. */
+			file but 5.5 only 5M. Thus give hint to user. */
+ 			fprintf(stderr,
+				"InnoDB: Error: log file %s is"
+ 				" of different size %lu %lu bytes\n"
+ 				"InnoDB: than specified in the .cnf"
+ 				" file %lu %lu bytes!\n",
+ 				name, (ulong) size_high, (ulong) size,
+ 				(ulong) srv_calc_high32(srv_log_file_size),
+ 				(ulong) srv_calc_low32(srv_log_file_size));
+
 			fprintf(stderr,
-				"InnoDB: Warning: log file %s is"
-				" of different size %lu %lu bytes\n"
-				"InnoDB: than specified in the .cnf"
-				" file %lu %lu bytes!\n",
-				name, (ulong) size_high, (ulong) size,
-				(ulong) srv_calc_high32(srv_log_file_size),
-				(ulong) srv_calc_low32(srv_log_file_size));
+				"InnoDB: Possible causes for this error:\n"
+				" (a) Incorrect log file is used or log file size is changed\n"
+				" (b) In case default size is used this log file is from 10.0\n"
+				" (c) Log file is corrupted or there was not enough disk space\n"
+				" In case (b) you need to set innodb_log_file_size = 48M\n");
+
+			return(DB_ERROR);
 		}
 	} else {
 		*log_file_created = TRUE;