Bug#22119 - Changing MI_KEY_BLOCK_LENGTH makes a wrong myisamchk

When compiling with a default key block size greater than the
smallest key block size used in a table, checking that table
failed with bogus errors. The table was marked corrupt. This
affected myisamchk and the server.

The problem was that the default key block size was used at
some places where sizes less or equal to the block size of the
index in check was required.

We do now use the key block size of the particular index
when checking.

A test case is available for later versions only.

myisam/mi_check.c

@@ -251,11 +251,12 @@ static int check_k_link(MI_CHECK *param, register MI_INFO *info, uint nr)
   my_off_t next_link;
   uint block_size=(nr+1)*MI_MIN_KEY_BLOCK_LENGTH;
   ha_rows records;
-  char llbuff[21],*buff;
+  char llbuff[21], llbuff2[21], *buff;
   DBUG_ENTER("check_k_link");
+  DBUG_PRINT("enter", ("block_size: %u", block_size));
 
   if (param->testflag & T_VERBOSE)
-    printf("block_size %4d:",block_size);
+    printf("block_size %4u:", block_size); /* purecov: tested */
 
   next_link=info->s->state.key_del[nr];
   records= (ha_rows) (info->state->key_file_length / block_size);
@@ -265,14 +266,46 @@ static int check_k_link(MI_CHECK *param, register MI_INFO *info, uint nr)
       DBUG_RETURN(1);
     if (param->testflag & T_VERBOSE)
       printf("%16s",llstr(next_link,llbuff));
-    if (next_link > info->state->key_file_length ||
-	next_link & (info->s->blocksize-1))
+
+    /* Key blocks must lay within the key file length entirely. */
+    if (next_link + block_size > info->state->key_file_length)
+    {
+      /* purecov: begin tested */
+      mi_check_print_error(param, "Invalid key block position: %s  "
+                           "key block size: %u  file_length: %s",
+                           llstr(next_link, llbuff), block_size,
+                           llstr(info->state->key_file_length, llbuff2));
+      DBUG_RETURN(1);
+      /* purecov: end */
+    }
+
+    /* Key blocks must be aligned at MI_MIN_KEY_BLOCK_LENGTH. */
+    if (next_link & (MI_MIN_KEY_BLOCK_LENGTH - 1))
+    {
+      /* purecov: begin tested */
+      mi_check_print_error(param, "Mis-aligned key block: %s  "
+                           "minimum key block length: %u",
+                           llstr(next_link, llbuff), MI_MIN_KEY_BLOCK_LENGTH);
       DBUG_RETURN(1);
+      /* purecov: end */
+    }
+
+    /*
+      Read the key block with MI_MIN_KEY_BLOCK_LENGTH to find next link.
+      If the key cache block size is smaller than block_size, we can so
+      avoid unecessary eviction of cache block.
+    */
     if (!(buff=key_cache_read(info->s->key_cache,
                               info->s->kfile, next_link, DFLT_INIT_HITS,
-                              (byte*) info->buff,
-			      myisam_block_size, block_size, 1)))
+                              (byte*) info->buff, MI_MIN_KEY_BLOCK_LENGTH,
+                              MI_MIN_KEY_BLOCK_LENGTH, 1)))
+    {
+      /* purecov: begin tested */
+      mi_check_print_error(param, "key cache read error for block: %s",
+			   llstr(next_link,llbuff));
       DBUG_RETURN(1);
+      /* purecov: end */
+    }
     next_link=mi_sizekorr(buff);
     records--;
     param->key_file_blocks+=block_size;
@@ -555,17 +588,37 @@ static int chk_index_down(MI_CHECK *param, MI_INFO *info, MI_KEYDEF *keyinfo,
                      ha_checksum *key_checksum, uint level)
 {
   char llbuff[22],llbuff2[22];
-  if (page > info->state->key_file_length || (page & (info->s->blocksize -1)))
-  {
-    my_off_t max_length=my_seek(info->s->kfile,0L,MY_SEEK_END,MYF(0));
-    mi_check_print_error(param,"Wrong pagepointer: %s at page: %s",
-                llstr(page,llbuff),llstr(page,llbuff2));
-
-    if (page+info->s->blocksize > max_length)
+  DBUG_ENTER("chk_index_down");
+
+  /* Key blocks must lay within the key file length entirely. */
+  if (page + keyinfo->block_length > info->state->key_file_length)
+  {
+    /* purecov: begin tested */
+    /* Give it a chance to fit in the real file size. */
+    my_off_t max_length= my_seek(info->s->kfile, 0L, MY_SEEK_END, MYF(0));
+    mi_check_print_error(param, "Invalid key block position: %s  "
+                         "key block size: %u  file_length: %s",
+                         llstr(page, llbuff), keyinfo->block_length,
+                         llstr(info->state->key_file_length, llbuff2));
+    if (page + keyinfo->block_length > max_length)
       goto err;
-    info->state->key_file_length=(max_length &
-                                  ~ (my_off_t) (info->s->blocksize-1));
+    /* Fix the remebered key file length. */
+    info->state->key_file_length= (max_length &
+                                   ~ (my_off_t) (keyinfo->block_length - 1));
+    /* purecov: end */
+  }
+
+  /* Key blocks must be aligned at MI_MIN_KEY_BLOCK_LENGTH. */
+  if (page & (MI_MIN_KEY_BLOCK_LENGTH - 1))
+  {
+    /* purecov: begin tested */
+    mi_check_print_error(param, "Mis-aligned key block: %s  "
+                         "minimum key block length: %u",
+                         llstr(page, llbuff), MI_MIN_KEY_BLOCK_LENGTH);
+    goto err;
+    /* purecov: end */
   }
+
   if (!_mi_fetch_keypage(info,keyinfo,page, DFLT_INIT_HITS,buff,0))
   {
     mi_check_print_error(param,"Can't read key from filepos: %s",
@@ -576,9 +629,12 @@ static int chk_index_down(MI_CHECK *param, MI_INFO *info, MI_KEYDEF *keyinfo,
   if (chk_index(param,info,keyinfo,page,buff,keys,key_checksum,level))
     goto err;
 
-  return 0;
+  DBUG_RETURN(0);
+
+  /* purecov: begin tested */
 err:
-  return 1;
+  DBUG_RETURN(1);
+  /* purecov: end */
 }