Information in input filter hook_filter from where it was called node-view, block-view, ...

Does anybody know, if it is possible and how to get the information inside the hook_filter from where it was called. I have a filter that should take care to run a normally nodeapi fired filter also when $text was send to my filter by block-view etc.

function myhook_filter($op, ...) {
  
  switch ($called-by) {

    case 'block':
      do this;

    default:
      do that;

Thanx for your help