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, 5 insertions, 0 deletions

diff --git a/util/notify.c b/util/notify.c
index aee8d93cb0..76bab212ae 100644
--- a/util/notify.c
+++ b/util/notify.c
@@ -40,6 +40,11 @@ void notifier_list_notify(NotifierList *list, void *data)
     }
 }
 
+bool notifier_list_empty(NotifierList *list)
+{
+    return QLIST_EMPTY(&list->notifiers);
+}
+
 void notifier_with_return_list_init(NotifierWithReturnList *list)
 {
     QLIST_INIT(&list->notifiers);