bzr commit into mysql-backup-backport branch (charles.bell:3051) Bug#30938

[Chuck Bell]

#At file:///Users/cbell/source/bzr/MS10/ based on revid:charles.bell@stripped

 3051 Chuck Bell	2010-01-11
      BUG#30938 (BACKUP DATABASE crashes server if a table with a unloaded 
      SE exists).
      
      Backup of a database failed if it contained a table using invalid storage
      engine (e.g. plugin not loaded or unknown engine). This was because code
      collecting list of tables in a database (Backup_archive::add_db_items() in 
      sql_backup.cc) didn't exclude tables without a valid storage engine and later 
      kernel attempted to open such tables. This patch fixes this by filtering out 
      tables for which 'engine' field in I_S.TABLES is NULL.
      
      Additionally, the way we access handlerton structure of table's storage engine 
      has been changed. Before, we located SE plugin sing its name and then read 
      handlerton pointer from the plugin:
      
        plugin= ::ha_resolve_by_name(::current_thd,&name_lex);
        m_hton= plugin ? plugin_data(plugin, handlerton*) : 0;
      
      Now we open a table and read handlerton pointer from opened TABLE structure. 
      This is safer because it gives the open table code a chance to detect/deal with 
      non-existent or non-functional storage engines. If a table was opened 
      successfully we assume that its storage engine is fully functional.
      
      Tables are opened just before they are added to the archive inside 
      Backup_archive::add_db_items(). Each table is closed after it has been added so 
      that only one table is open at a time.
      
      original changeset: 2476.776.2

    added:
      mysql-test/std_data/bug30938.frm
=== added file 'mysql-test/std_data/bug30938.frm'
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