[PATCH 10/11] mini-os/xenbus: Provide queue->wakeup hook

[Ian Jackson <ian.jackson@eu.citrix.com>]

This allows xenbus's caller to get called back when an item is put on
the queue, rather than simply having the waitq signaled.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
---
 include/mini-os/xenbus.h |   15 +++++++++++++++
 xen/xenbus/xenbus.c      |    8 +++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/mini-os/xenbus.h b/include/mini-os/xenbus.h
index a811c19..1900e55 100644
--- a/include/mini-os/xenbus.h
+++ b/include/mini-os/xenbus.h
@@ -46,6 +46,7 @@ struct xenbus_event {
 };
 struct xenbus_event_queue {
     MINIOS_STAILQ_HEAD(, xenbus_event) events;
+    void (*wakeup)(struct xenbus_event_queue*); /* can be safely ignored */
     struct wait_queue_head waitq;
 };
 
@@ -129,6 +130,20 @@ domid_t xenbus_get_self_id(void);
  * ----- asynchronous low-level interface -----
  */
 
+/*
+ * Use of queue->wakeup:
+ *
+ * If queue->wakeup is set, it will be called instead of
+ * wake_up(&queue->waitq);
+ *
+ * queue->wakeup is initialised (to a function which just calls
+ * wake_up) by xenbus_event_queue_init.  The user who wants something
+ * different should set ->wakeup after the init, but before the queue
+ * is used for xenbus_id_allocate or xenbus_watch_prepare.
+ *
+ * queue->wakeup() is called with the req_lock held.
+ */
+
 /* Allocate an identifier for a xenbus request.  Blocks if none are
  * available.  Cannot fail.  On return, we may use the returned value
  * as the id in a xenbus request.
diff --git a/xen/xenbus/xenbus.c b/xen/xenbus/xenbus.c
index 7b391c5..e5d7f36 100644
--- a/xen/xenbus/xenbus.c
+++ b/xen/xenbus/xenbus.c
@@ -67,9 +67,15 @@ spinlock_t xenbus_req_lock = SPIN_LOCK_UNLOCKED;
  *    watches
  */
 
+static void queue_wakeup(struct xenbus_event_queue *queue)
+{
+    wake_up(&queue->waitq);
+}
+
 void xenbus_event_queue_init(struct xenbus_event_queue *queue)
 {
     MINIOS_STAILQ_INIT(&queue->events);
+    queue->wakeup = queue_wakeup;
     init_waitqueue_head(&queue->waitq);
 }
 
@@ -92,7 +98,7 @@ static void queue_event(struct xenbus_event_queue *queue,
 {
     /* Called with lock held */
     MINIOS_STAILQ_INSERT_TAIL(&queue->events, event, entry);
-    wake_up(&queue->waitq);
+    queue->wakeup(queue);
 }
 
 static struct xenbus_event *await_event(struct xenbus_event_queue *queue)
-- 
1.7.10.4