2:15 p.m.
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