warning when a 4.1 MYI file is opened in 4.0

myisam/mi_open.c

@@ -182,6 +182,9 @@ MI_INFO *mi_open(const char *name, int mode, uint open_flags)
     }
     share->state_diff_length=len-MI_STATE_INFO_SIZE;
 
+    if (share->state.header.fulltext_keys)
+      fprintf(stderr, "Table file %s was created in MySQL 4.1+, use REPAIR TABLE ... USE_FRM to recreate it as a valid MySQL 4.0 table\n", name_buff);
+
     mi_state_info_read(disk_cache, &share->state);
     len= mi_uint2korr(share->state.header.base_info_length);
     if (len != MI_BASE_INFO_SIZE)

myisam/myisamdef.h

@@ -55,7 +55,8 @@ typedef struct st_mi_state_info
     uchar uniques;			/* number of UNIQUE definitions */
     uchar language;			/* Language for indexes */
     uchar max_block_size;		/* max keyblock size */
-    uchar not_used[2];			/* To align to 8 */
+    uchar fulltext_keys;                /* reserved for 4.1 */
+    uchar not_used;			/* To align to 8 */
   } header;
 
   MI_STATUS_INFO state;