media: v4l2-dev: Add v4l2_device_register_ro_subdev_node()

Add to the V4L2 core a function to register device nodes for video
subdevices in read-only mode.

Registering a device node in read-only mode is useful to expose to
userspace the current sub-device configuration, without allowing
application to change it by using the V4L2 subdevice ioctls.

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

2 files changed, 53 insertions, 4 deletions

diff --git a/include/media/v4l2-dev.h b/include/media/v4l2-dev.h
index 4602c15ff878..ad2d41952442 100644
--- a/include/media/v4l2-dev.h
+++ b/include/media/v4l2-dev.h
@@ -82,11 +82,18 @@ struct v4l2_ctrl_handler;
  *	but the old crop API will still work as expected in order to preserve
  *	backwards compatibility.
  *	Never set this flag for new drivers.
+ * @V4L2_FL_SUBDEV_RO_DEVNODE:
+ *	indicates that the video device node is registered in read-only mode.
+ *	The flag only applies to device nodes registered for sub-devices, it is
+ *	set by the core when the sub-devices device nodes are registered with
+ *	v4l2_device_register_ro_subdev_nodes() and used by the sub-device ioctl
+ *	handler to restrict access to some ioctl calls.
  */
 enum v4l2_video_device_flags {
 	V4L2_FL_REGISTERED		= 0,
 	V4L2_FL_USES_V4L2_FH		= 1,
 	V4L2_FL_QUIRK_INVERTED_CROP	= 2,
+	V4L2_FL_SUBDEV_RO_DEVNODE	= 3,
 };
 
 /* Priority helper functions */
diff --git a/include/media/v4l2-device.h b/include/media/v4l2-device.h
index 7c912b7d2870..64ec4de948e9 100644
--- a/include/media/v4l2-device.h
+++ b/include/media/v4l2-device.h
@@ -174,14 +174,56 @@ int __must_check v4l2_device_register_subdev(struct v4l2_device *v4l2_dev,
 void v4l2_device_unregister_subdev(struct v4l2_subdev *sd);
 
 /**
- * v4l2_device_register_subdev_nodes - Registers device nodes for all subdevs
- *	of the v4l2 device that are marked with
- *	the %V4L2_SUBDEV_FL_HAS_DEVNODE flag.
+ * __v4l2_device_register_ro_subdev_nodes - Registers device nodes for
+ *      all subdevs of the v4l2 device that are marked with the
+ *      %V4L2_SUBDEV_FL_HAS_DEVNODE flag.
  *
  * @v4l2_dev: pointer to struct v4l2_device
+ * @read_only: subdevices read-only flag. True to register the subdevices
+ *	device nodes in read-only mode, false to allow full access to the
+ *	subdevice userspace API.
  */
 int __must_check
-v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev);
+__v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev,
+				    bool read_only);
+
+/**
+ * v4l2_device_register_subdev_nodes - Registers subdevices device nodes with
+ *	unrestricted access to the subdevice userspace operations
+ *
+ * Internally calls __v4l2_device_register_subdev_nodes(). See its documentation
+ * for more details.
+ *
+ * @v4l2_dev: pointer to struct v4l2_device
+ */
+static inline int __must_check
+v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
+{
+#if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
+	return __v4l2_device_register_subdev_nodes(v4l2_dev, false);
+#else
+	return 0;
+#endif
+}
+
+/**
+ * v4l2_device_register_ro_subdev_nodes - Registers subdevices device nodes
+ *	in read-only mode
+ *
+ * Internally calls __v4l2_device_register_subdev_nodes(). See its documentation
+ * for more details.
+ *
+ * @v4l2_dev: pointer to struct v4l2_device
+ */
+static inline int __must_check
+v4l2_device_register_ro_subdev_nodes(struct v4l2_device *v4l2_dev)
+{
+#if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
+	return __v4l2_device_register_subdev_nodes(v4l2_dev, true);
+#else
+	return 0;
+#endif
+}
 
 /**
  * v4l2_subdev_notify - Sends a notification to v4l2_device.