[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>

2 files changed, 27 insertions, 0 deletions

diff --git a/drivers/media/video/v4l2-fh.c b/drivers/media/video/v4l2-fh.c
index 27242e5ca431..543b3fe6784e 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);
diff --git a/include/media/v4l2-fh.h b/include/media/v4l2-fh.h
index 5657881cd44e..0206aa55be24 100644
--- a/include/media/v4l2-fh.h
+++ b/include/media/v4l2-fh.h
@@ -77,5 +77,18 @@ void v4l2_fh_exit(struct v4l2_fh *fh);
  * v4l2_fh struct) is NULL. This function always returns 0.
  */
 int v4l2_fh_release(struct file *filp);
+/*
+ * Returns 1 if this filehandle is the only filehandle opened for the
+ * associated video_device. If fh is NULL, then it returns 0.
+ */
+int v4l2_fh_is_singular(struct v4l2_fh *fh);
+/*
+ * Helper function with struct file as argument. If filp->private_data is
+ * NULL, then it will return 0.
+ */
+static inline int v4l2_fh_is_singular_file(struct file *filp)
+{
+        return v4l2_fh_is_singular(filp->private_data);
+}
 
 #endif /* V4L2_EVENT_H */