xen: allow to register event channels without handlers

This is needed by the event channel user-space device, that requires
registering event channels without unmasking them. intr_add_handler
will unconditionally unmask the event channel, so we avoid calling it
if no filter/handler is provided, and then the user will be in charge
of calling it when ready.

In order to do this, we need to change the opaque type
xen_intr_handle_t to contain the event channel port instead of the
opaque cookie returned by intr_add_handler, since now registration of
event channels without handlers are allowed. The cookie will now be
stored inside of the private xenisrc struct. Also, introduce a new
function called xen_intr_add_handler that allows adding a
filter/handler after the event channel has been registered.

Sponsored by: Citrix Systems R&D

x86/xen/xen_intr.c:
 - Leave the event channel without a handler if no filter/handler is
   provided to xen_intr_bind_isrc.
 - Don't perform an evtchn_mask_port, intr_add_handler will already do
   it.
 - Change the opaque type xen_intr_handle_t to contain a pointer to
   the event channel port number, and make the necessary changes to
   related functions.
 - Introduce a new function called xen_intr_add_handler that can be
   used to add filter/handlers to an event channel after registration.

xen/xen_intr.h:
 - Add prototype of xen_intr_add_handler.

1 files changed, 19 insertions, 0 deletions

diff --git a/sys/xen/xen_intr.h b/sys/xen/xen_intr.h
index a29414d..d2d6470 100644
--- a/sys/xen/xen_intr.h
+++ b/sys/xen/xen_intr.h
@@ -246,4 +246,23 @@ int xen_register_msi(device_t dev, int vector, int count);
  */
 int xen_release_msi(int vector);
 
+/**
+ * Bind an event channel port with a handler
+ *
+ * \param dev       The device making this bind request.
+ * \param filter    An interrupt filter handler.  Specify NULL
+ *                  to always dispatch to the ithread handler.
+ * \param handler   An interrupt ithread handler.  Optional (can
+ *                  specify NULL) if all necessary event actions
+ *                  are performed by filter.
+ * \param arg       Argument to present to both filter and handler.
+ * \param irqflags  Interrupt handler flags.  See sys/bus.h.
+ * \param handle    Opaque handle used to manage this registration.
+ *
+ * \returns  0 on success, otherwise an errno.
+ */
+int xen_intr_add_handler(device_t dev, driver_filter_t filter,
+	driver_intr_t handler, void *arg, enum intr_type flags,
+	xen_intr_handle_t handle);
+
 #endif /* _XEN_INTR_H_ */