event_notifier: add event_notifier_set

EventNotifier right now cannot be used as an inter-thread communication
primitive.  It only works if something else (the kernel) sets the eventfd.
Add a primitive to signal an EventNotifier that another thread is waiting
on.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/event_notifier.c b/event_notifier.c
index 0b829813d3..2b210f4b44 100644
--- a/event_notifier.c
+++ b/event_notifier.c
@@ -38,6 +38,13 @@ int event_notifier_get_fd(EventNotifier *e)
     return e->fd;
 }
 
+int event_notifier_set(EventNotifier *e)
+{
+    uint64_t value = 1;
+    int r = write(e->fd, &value, sizeof(value));
+    return r == sizeof(value);
+}
+
 int event_notifier_test_and_clear(EventNotifier *e)
 {
     uint64_t value;