journal_dirty_data — mark a buffer as containing dirty data to be flushed
transaction
bufferhead to mark
Mark a buffer as containing dirty data which needs to be flushed before we can commit the current transaction.
The buffer is placed on the transaction's data list and is marked as belonging to the transaction.
Returns error number or 0 on success.
journal_dirty_data can be called via page_launder->ext3_writepage by kswapd.