notifier: event notifier implementation
event notifiers are slightly generalized eventfd descriptors. Current
implementation depends on eventfd because vhost is the only user, and
vhost depends on eventfd anyway, but a stub is provided for non-eventfd
case.
We'll be able to further generalize this when another user comes along
and we see how to best do this.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/hw/event_notifier.c b/hw/event_notifier.c
new file mode 100644
index 0000000..13f3656
--- /dev/null
+++ b/hw/event_notifier.c
@@ -0,0 +1,62 @@
+/*
+ * event notifier support
+ *
+ * Copyright Red Hat, Inc. 2010
+ *
+ * Authors:
+ * Michael S. Tsirkin <mst@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2. See
+ * the COPYING file in the top-level directory.
+ */
+
+#include "hw.h"
+#include "event_notifier.h"
+#ifdef CONFIG_EVENTFD
+#include <sys/eventfd.h>
+#endif
+
+int event_notifier_init(EventNotifier *e, int active)
+{
+#ifdef CONFIG_EVENTFD
+ int fd = eventfd(!!active, EFD_NONBLOCK | EFD_CLOEXEC);
+ if (fd < 0)
+ return -errno;
+ e->fd = fd;
+ return 0;
+#else
+ return -ENOSYS;
+#endif
+}
+
+void event_notifier_cleanup(EventNotifier *e)
+{
+ close(e->fd);
+}
+
+int event_notifier_get_fd(EventNotifier *e)
+{
+ return e->fd;
+}
+
+int event_notifier_test_and_clear(EventNotifier *e)
+{
+ uint64_t value;
+ int r = read(e->fd, &value, sizeof(value));
+ return r == sizeof(value);
+}
+
+int event_notifier_test(EventNotifier *e)
+{
+ uint64_t value;
+ int r = read(e->fd, &value, sizeof(value));
+ if (r == sizeof(value)) {
+ /* restore previous value. */
+ int s = write(e->fd, &value, sizeof(value));
+ /* never blocks because we use EFD_SEMAPHORE.
+ * If we didn't we'd get EAGAIN on overflow
+ * and we'd have to write code to ignore it. */
+ assert(s == sizeof(value));
+ }
+ return r == sizeof(value);
+}
