media: v4l2-dev/event: add v4l2_event_wake_all()

When unregistering a V4L2 device node, make sure any filehandles
that are waiting for an event are woken up.

Add v4l2_event_wake_all() to v4l2-event.c and call it from
video_unregister_device().

Otherwise userspace might never know that a device node was removed.

[hverkuil: checkpatch: replaced 'if (vdev == NULL)' by 'if (!vdev)']
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/v4l2-core/v4l2-dev.c

@@ -28,6 +28,7 @@
 #include <media/v4l2-common.h>
 #include <media/v4l2-device.h>
 #include <media/v4l2-ioctl.h>
+#include <media/v4l2-event.h>
 
 #define VIDEO_NUM_DEVICES	256
 #define VIDEO_NAME              "video4linux"
@@ -1086,6 +1087,8 @@ void video_unregister_device(struct video_device *vdev)
 	 */
 	clear_bit(V4L2_FL_REGISTERED, &vdev->flags);
 	mutex_unlock(&videodev_lock);
+	if (test_bit(V4L2_FL_USES_V4L2_FH, &vdev->flags))
+		v4l2_event_wake_all(vdev);
 	device_unregister(&vdev->dev);
 }
 EXPORT_SYMBOL(video_unregister_device);

drivers/media/v4l2-core/v4l2-event.c

@@ -187,6 +187,23 @@ int v4l2_event_pending(struct v4l2_fh *fh)
 }
 EXPORT_SYMBOL_GPL(v4l2_event_pending);
 
+void v4l2_event_wake_all(struct video_device *vdev)
+{
+	struct v4l2_fh *fh;
+	unsigned long flags;
+
+	if (!vdev)
+		return;
+
+	spin_lock_irqsave(&vdev->fh_lock, flags);
+
+	list_for_each_entry(fh, &vdev->fh_list, list)
+		wake_up_all(&fh->wait);
+
+	spin_unlock_irqrestore(&vdev->fh_lock, flags);
+}
+EXPORT_SYMBOL_GPL(v4l2_event_wake_all);
+
 static void __v4l2_event_unsubscribe(struct v4l2_subscribed_event *sev)
 {
 	struct v4l2_fh *fh = sev->fh;

include/media/v4l2-event.h

@@ -101,7 +101,7 @@ int v4l2_event_dequeue(struct v4l2_fh *fh, struct v4l2_event *event,
  *
  * .. note::
  *    The driver's only responsibility is to fill in the type and the data
- *    fields.The other fields will be filled in by  V4L2.
+ *    fields. The other fields will be filled in by V4L2.
  */
 void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev);
 
@@ -116,10 +116,19 @@ void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev);
  *
  * .. note::
  *    The driver's only responsibility is to fill in the type and the data
- *    fields.The other fields will be filled in by  V4L2.
+ *    fields. The other fields will be filled in by V4L2.
  */
 void v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *ev);
 
+/**
+ * v4l2_event_wake_all - Wake all filehandles.
+ *
+ * Used when unregistering a video device.
+ *
+ * @vdev: pointer to &struct video_device
+ */
+void v4l2_event_wake_all(struct video_device *vdev);
+
 /**
  * v4l2_event_pending - Check if an event is available
  *