xen / notify: introduce a new XenWatchList abstraction

Xenstore watch call-backs are already abstracted away from XenBus using
the XenWatch data structure but the associated NotifierList manipulation
and file handle registration is still open coded in various xen_bus_...()
functions.
This patch creates a new XenWatchList data structure to allow these
interactions to be abstracted away from XenBus as well. This is in
preparation for a subsequent patch which will introduce separate watch lists
for XenBus and XenDevice objects.

NOTE: This patch also introduces a new notifier_list_empty() helper function
      for the purposes of adding an assertion that a XenWatchList is not
      freed whilst its associated NotifierList is still occupied.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony Perard <anthony.perard@citrix.com>
Message-Id: <20190913082159.31338-2-paul.durrant@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/qemu/notify.h b/include/qemu/notify.h
index a3d73e4bc7..bcfa70fb2e 100644
--- a/include/qemu/notify.h
+++ b/include/qemu/notify.h
@@ -40,6 +40,8 @@ void notifier_remove(Notifier *notifier);
 
 void notifier_list_notify(NotifierList *list, void *data);
 
+bool notifier_list_empty(NotifierList *list);
+
 /* Same as Notifier but allows .notify() to return errors */
 typedef struct NotifierWithReturn NotifierWithReturn;