How do I identify filtered rows in my datatable ?? ...

I'm using the select plugin and want to be able to have a button to select ALL the rows which meet the current global filter condition .. How do i identify rows that are 'visible' .. ie meet the filter .. Currently I have a button which just does

   dt.rows().select(); 

but this (obviously) selects all the rows regardless . I just want the ones that match the current global filter .. I expect it to be trivial but I can't find it in the documentation ..

Thanks in advance ..