Okay, at long last, I see what you mean (I think). Apps using libvirt events must register an EventImpl via virRegisterEventImpl. Internally, suppose we implement events via an anonymous pipe. libvirt would call EventImpl.addHandle(pipe_read_fd, POLLIN ..., __virHandleEvents, conn) so the app's main loop would monitor fd (in whatever manner it chooses), then call __virHandleEvents(fd, conn) when it detected activity. __virHandleEvents would pull the event from the pipe and dispatch handlers as appropriate. We'd call eventImpl.removeHandle(pipe_read_fd) when the domain goes away. Am I finally on the right track?? If so, are you proposing that we simply make the existing src/events.h interface public? At this point, I don't see the need for anything but addHandle and removeHandle (but I can see how the others might be useful to libvirt eventually). Dave On Mon, 2008-09-22 at 16:22 +0100, Daniel P. Berrange wrote:
No, this the wrong approach. This is defining an event loop impl - we don't want todo that. We need to define an API to let an application provide a set of callback for libvirt to talk to an existing event loop impl. ie a way for libvirt to register FD watches and timeouts, not a way for apps to manually process libvirt events in this way this example shows.
The public API for this is along the lines of that currently defined in the src/events.h file.
There are a set of functions libvirt needs in order to register actions for FDs, and/or timeouts. So the public API should consist of a way to register impls of these APIs
typedef int (*virEventAddHandleFunc)(int, int, virEventHandleCallback, void *); typedef void (*virEventUpdateHandleFunc)(int, int); typedef int (*virEventRemoveHandleFunc)(int);
typedef int (*virEventAddTimeoutFunc)(int, virEventTimeoutCallback, void *); typedef void (*virEventUpdateTimeoutFunc)(int, int); typedef int (*virEventRemoveTimeoutFunc)(int);
void virEventRegisterImpl(virEventAddHandleFunc addHandle, virEventUpdateHandleFunc updateHandle, virEventRemoveHandleFunc removeHandle, virEventAddTimeoutFunc addTimeout, virEventUpdateTimeoutFunc updateTimeout, virEventRemoveTimeoutFunc removeTimeout);
A separate libvirt-glib.so, would provide a API call
virEventRegisterGLib()
which calls virEventRegisterImpl() with a suitable implementation for glib. An application like virt-manager which uses glib and wants events would then calll virEventRegisterGLib(). If it had a custom event loop of its own, then it could call virEventRegisterImpl() directly with its special impl.
It may be worth making our public API even more closely aligned with dbus - see dbus-connection.h and dbus-server.h - so people writing glue functions for it could just reuse what they've already written for dbus.
typedef dbus_bool_t (* DBusAddWatchFunction) (DBusWatch *watch, void *data); typedef void (* DBusWatchToggledFunction) (DBusWatch *watch, void *data); typedef void (* DBusRemoveWatchFunction) (DBusWatch *watch, void *data);
typedef dbus_bool_t (* DBusAddTimeoutFunction) (DBusTimeout *timeout, void *data); typedef void (* DBusTimeoutToggledFunction) (DBusTimeout *timeout, void *data); typedef void (* DBusRemoveTimeoutFunction) (DBusTimeout *timeout, void *data);
dbus_bool_t dbus_server_set_watch_functions (DBusServer *server, DBusAddWatchFunction add_function, DBusRemoveWatchFunction remove_function, DBusWatchToggledFunction toggled_function, void *data, DBusFreeFunction free_data_function); dbus_bool_t dbus_server_set_timeout_functions (DBusServer *server, DBusAddTimeoutFunction add_function, DBusRemoveTimeoutFunction remove_function, DBusTimeoutToggledFunction toggled_function, void *data, DBusFreeFunction free_data_function);
A 'watch' in DBus terminology is a file descriptor monitor.
Daniel