[libvirt] [RFC] Events API
David Lively
dlively at virtualiron.com
Mon Sep 22 19:15:25 UTC 2008
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
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