[media] v4l2-fh: add v4l2_fh_is_singular

Several drivers need to do something when the first filehandle is opened
or the last filehandle is closed. Most implement some use count mechanism,
but if they use v4l2_fh, then you can also just check if this is the only
filehandle for the device node. A simple helper function can do this.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/drivers/media/video/v4l2-fh.c b/drivers/media/video/v4l2-fh.c
index 27242e5ca43..543b3fe6784 100644
--- a/drivers/media/video/v4l2-fh.c
+++ b/drivers/media/video/v4l2-fh.c
@@ -109,3 +109,17 @@ int v4l2_fh_release(struct file *filp)
 	return 0;
 }
 EXPORT_SYMBOL_GPL(v4l2_fh_release);
+
+int v4l2_fh_is_singular(struct v4l2_fh *fh)
+{
+	unsigned long flags;
+	int is_singular;
+
+	if (fh == NULL || fh->vdev == NULL)
+		return 0;
+	spin_lock_irqsave(&fh->vdev->fh_lock, flags);
+	is_singular = list_is_singular(&fh->list);
+	spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
+	return is_singular;
+}
+EXPORT_SYMBOL_GPL(v4l2_fh_is_singular);