[media] v4l2-fh: add v4l2_fh_open and v4l2_fh_release helper functions

Add two new functions: v4l2_fh_open allocates and initializes a struct v4l2_fh
based on a struct file pointer and v4l2_fh_release releases and frees a struct
v4l2_fh.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/v4l2-fh.c

@@ -23,6 +23,7 @@
  */
 
 #include <linux/bitops.h>
+#include <linux/slab.h>
 #include <media/v4l2-dev.h>
 #include <media/v4l2-fh.h>
 #include <media/v4l2-event.h>
@@ -60,6 +61,20 @@ void v4l2_fh_add(struct v4l2_fh *fh)
 }
 EXPORT_SYMBOL_GPL(v4l2_fh_add);
 
+int v4l2_fh_open(struct file *filp)
+{
+	struct video_device *vdev = video_devdata(filp);
+	struct v4l2_fh *fh = kzalloc(sizeof(*fh), GFP_KERNEL);
+
+	filp->private_data = fh;
+	if (fh == NULL)
+		return -ENOMEM;
+	v4l2_fh_init(fh, vdev);
+	v4l2_fh_add(fh);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(v4l2_fh_open);
+
 void v4l2_fh_del(struct v4l2_fh *fh)
 {
 	unsigned long flags;
@@ -81,3 +96,16 @@ void v4l2_fh_exit(struct v4l2_fh *fh)
 	v4l2_event_free(fh);
 }
 EXPORT_SYMBOL_GPL(v4l2_fh_exit);
+
+int v4l2_fh_release(struct file *filp)
+{
+	struct v4l2_fh *fh = filp->private_data;
+
+	if (fh) {
+		v4l2_fh_del(fh);
+		v4l2_fh_exit(fh);
+		kfree(fh);
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(v4l2_fh_release);

include/media/v4l2-fh.h

@@ -50,9 +50,17 @@ int v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev);
  * handle must be initialised first.
  */
 void v4l2_fh_add(struct v4l2_fh *fh);
+/*
+ * Can be used as the open() op of v4l2_file_operations.
+ * It allocates a v4l2_fh and inits and adds it to the video_device associated
+ * with the file pointer.
+ */
+int v4l2_fh_open(struct file *filp);
 /*
  * Remove file handle from the list of file handles. Must be called in
  * v4l2_file_operations->release() handler if the driver uses v4l2_fh.
+ * On error filp->private_data will be NULL, otherwise it will point to
+ * the v4l2_fh struct.
  */
 void v4l2_fh_del(struct v4l2_fh *fh);
 /*
@@ -62,5 +70,12 @@ void v4l2_fh_del(struct v4l2_fh *fh);
  * driver uses v4l2_fh.
  */
 void v4l2_fh_exit(struct v4l2_fh *fh);
+/*
+ * Can be used as the release() op of v4l2_file_operations.
+ * It deletes and exits the v4l2_fh associated with the file pointer and
+ * frees it. It will do nothing if filp->private_data (the pointer to the
+ * v4l2_fh struct) is NULL. This function always returns 0.
+ */
+int v4l2_fh_release(struct file *filp);
 
 #endif /* V4L2_EVENT_H */