After some debugging I found, that when ‘presave’ op for nodeapi is called for node revert,  the $node object has vid for the version to be reverted to and when the node is being updated, the vid is the latest vid. So, fetching the current vid of the $node in ‘presave’ op and comparing it with the vid of the $node passed to presave operation, solved the problem. If the vid of the$node passed is same as the vid in the node table, then it is an update, else it is a node revert.

What about new node creation ? Well in case of new node creation the vid for $node is not set.

Here is the code snippet explaining the above logic


function mymodule_nodeapi(&$node, $op, $arg = 0){
  switch($op){
   case 'presave':
    if($node->vid){
      //node vid is set, means a this is edit or revision revert.
      $sql = 'select vid from {node} where nid=%d';
      $vid_db = db_fetch_array(db_query($sql,$node->vid));
      if($node->vid == $vid_db['vid']){
        //Execute edit logic.
      }else{
        //Execute revision revert logic.
      }
    }
  }
}