What is a downcall?

Answer 1

The term upcall is typically used in the context of using a framework, such as CORBA. When a request is sent from a client application to a server application, the framework is responsible for data marshalling, data transmission, and notification of the recipient that a request has been issued. An upcall is the call into the user code from the framework. This is typically supported through the use of a registered callback function registered either directly by the user, or indirectly through the mechanisms of the framework. An upcall is also called a callback.

Answer 2

unprivileged code privileged code enters kernel mode enters user mode implemented via trap implemented via IPC

---- Gernot Heiser 2002-08-21