What is linked permission?

Question

What is linked permission? The following is from authorization_manager.cpp.

   optional<permission_name> authorization_manager::lookup_linked_permission( account_name authorizer_account,
                                                                              account_name scope,
                                                                              action_name act_name
                                                                            )const
   {
      try {
         // First look up a specific link for this message act_name
         auto key = boost::make_tuple(authorizer_account, scope, act_name);
         auto link = _db.find<permission_link_object, by_action_name>(key);
         // If no specific link found, check for a contract-wide default
         if (link == nullptr) {
            boost::get<2>(key) = "";
            link = _db.find<permission_link_object, by_action_name>(key);
         }

         // If no specific or default link found, use active permission
         if (link != nullptr) {
            return link->required_permission;
         }
         return optional<permission_name>();

       //  return optional<permission_name>();
      } FC_CAPTURE_AND_RETHROW((authorizer_account)(scope)(act_name))
   }

Answer 1

One is able to request additional permissions for smart contract functions. That lookup function performs a look-up with the selected account and scope to find specific permissions that might exist for the function, and if nothing is found - uses a default permission. When you call an action from smart contract, you specify the permission for it:

action(permission_level {_self,N(active)}, account, N(adduser),
                std::make_tuple("lonkly", "Artem","Odessa",65014)).send();

and system verifies if that permission is eligible for that particular func.