More explicit error messages from myisamchk

myisam/mi_check.c:
  More explicit error messages
myisam/mi_dynrec.c:
  More comments

myisam/mi_check.c

@@ -200,21 +200,33 @@ int chk_del(MI_CHECK *param, register MI_INFO *info, uint test_flag)
 	empty+=info->s->base.pack_reclength;
       }
     }
+    if (test_flag & T_VERBOSE)
+      puts("\n");
     if (empty != info->state->empty)
     {
-      if (test_flag & T_VERBOSE) puts("");
       mi_check_print_warning(param,
-			     "Not used space is supposed to be: %s but is: %s",
-			     llstr(info->state->empty,buff),
-			     llstr(empty,buff2));
-      info->state->empty=empty;
+			     "Found %s deleted space in delete link chain. Should be %s",
+			     llstr(empty,buff2),
+			     llstr(info->state->empty,buff));
     }
-    if (i != 0 || next_link != HA_OFFSET_ERROR)
+    if (next_link != HA_OFFSET_ERROR)
+    {
+      mi_check_print_error(param,
+			   "Found more than the expected %s deleted rows in delete link chain",
+			   llstr(info->state->del, buff));
       goto wrong;
-
-    if (test_flag & T_VERBOSE) puts("\n");
+    }
+    if (i != 0)
+    {
+      mi_check_print_error(param,
+			   "Found %s deleted rows in delete link chain. Should be %s",
+			   llstr(info->state->del - i, buff2),
+			   llstr(info->state->del, buff));
+      goto wrong;
+    }
   }
   DBUG_RETURN(0);
+
 wrong:
   param->testflag|=T_RETRY_WITHOUT_QUICK;
   if (test_flag & T_VERBOSE) puts("");
@@ -1040,6 +1052,13 @@ int chk_data_link(MI_CHECK *param, MI_INFO *info,int extend)
     }
   }
 
+  if (del_length != info->state->empty)
+  {
+    mi_check_print_warning(param,
+			   "Found %s deleted space.   Should be %s",
+			   llstr(del_length,llbuff2),
+			   llstr(info->state->empty,llbuff));
+  }
   if (used+empty+del_length != info->state->data_file_length)
   {
     mi_check_print_warning(param,

myisam/mi_dynrec.c

@@ -167,7 +167,6 @@ static int _mi_find_writepos(MI_INFO *info,
   if (info->s->state.dellink != HA_OFFSET_ERROR)
   {
     /* Deleted blocks exists;  Get last used block */
-
     *filepos=info->s->state.dellink;
     block_info.second_read=0;
     info->rec_cache.seek_not_done=1;
@@ -211,7 +210,11 @@ static int _mi_find_writepos(MI_INFO *info,
 
 
 
-/* Remove a deleted block from the deleted list */
+/*
+  Unlink a deleted block from the deleted list.
+  This block will be combined with the preceding or next block to form
+  a big block.
+*/
 
 static bool unlink_deleted_block(MI_INFO *info, MI_BLOCK_INFO *block_info)
 {
@@ -225,6 +228,7 @@ static bool unlink_deleted_block(MI_INFO *info, MI_BLOCK_INFO *block_info)
   {
     MI_BLOCK_INFO tmp;
     tmp.second_read=0;
+    /* Unlink block from the previous block */
     if (!(_mi_get_block_info(&tmp,info->dfile,block_info->prev_filepos)
 	  & BLOCK_DELETED))
       DBUG_RETURN(1);				/* Something is wrong */
@@ -232,6 +236,7 @@ static bool unlink_deleted_block(MI_INFO *info, MI_BLOCK_INFO *block_info)
     if (my_pwrite(info->dfile,(char*) tmp.header+4,8,
 		  block_info->prev_filepos+4, MYF(MY_NABP)))
       DBUG_RETURN(1);
+    /* Unlink block from next block */
     if (block_info->next_filepos != HA_OFFSET_ERROR)
     {
       if (!(_mi_get_block_info(&tmp,info->dfile,block_info->next_filepos)
@@ -244,11 +249,16 @@ static bool unlink_deleted_block(MI_INFO *info, MI_BLOCK_INFO *block_info)
 	DBUG_RETURN(1);
     }
   }
+  /* We now have one less deleted block */
   info->state->del--;
   info->state->empty-= block_info->block_len;
   info->s->state.split--;
 
-  /* Removing block that we are using through mi_rrnd */
+  /*
+    If this was a block that we where accessing through table scan
+    (mi_rrnd() or mi_scan(), then ensure that we skip over this block
+    when doing next mi_rrnd() or mi_scan().
+  */
   if (info->nextpos == block_info->filepos)
     info->nextpos+=block_info->block_len;
   DBUG_RETURN(0);
@@ -325,7 +335,7 @@ static int delete_dynamic_record(MI_INFO *info, my_off_t filepos,
     info->state->empty+=length;
     filepos=block_info.next_filepos;
 
-    /* Now it's safe to unlink the block */
+    /* Now it's safe to unlink the deleted block directly after this one */
     if (remove_next_block && unlink_deleted_block(info,&del_block))
       error=1;
   } while (!(b_type & BLOCK_LAST));