Re: [libcamera-devel] [PATCH 2/4] media: v4l2-dev: Add v4l2_device_register_ro_subdev_node()

[Andrey Konovalov <andrey.konovalov@linaro.org>]

Hi Jacopo,

Thank you for your patch set!

On 24.03.2020 23:28, Jacopo Mondi wrote:
> Add to the V4L2 code 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.
> 
> Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
> ---
>   drivers/media/v4l2-core/v4l2-device.c | 16 +++++++++++++++-
>   drivers/media/v4l2-core/v4l2-subdev.c | 19 +++++++++++++++++++
>   include/media/v4l2-dev.h              |  7 +++++++
>   include/media/v4l2-device.h           | 10 ++++++++++
>   4 files changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-device.c b/drivers/media/v4l2-core/v4l2-device.c
> index 63d6b147b21e..6f9dba36eda1 100644
> --- a/drivers/media/v4l2-core/v4l2-device.c
> +++ b/drivers/media/v4l2-core/v4l2-device.c
> @@ -188,7 +188,8 @@ static void v4l2_device_release_subdev_node(struct video_device *vdev)
>   	kfree(vdev);
>   }
>   
> -int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
> +int __v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev,
> +					bool read_only)
>   {
>   	struct video_device *vdev;
>   	struct v4l2_subdev *sd;
> @@ -217,6 +218,8 @@ int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
>   		vdev->fops = &v4l2_subdev_fops;
>   		vdev->release = v4l2_device_release_subdev_node;
>   		vdev->ctrl_handler = sd->ctrl_handler;
> +		if (read_only)
> +			vdev->flags |= V4L2_FL_RO_DEVNODE;

<snip>

> @@ -331,6 +331,7 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
>   	struct v4l2_fh *vfh = file->private_data;
>   #if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
>   	struct v4l2_subdev_fh *subdev_fh = to_v4l2_subdev_fh(vfh);
> +	bool ro_devnode = !!(vdev->flags & V4L2_FL_RO_DEVNODE);

So V4L2_FL_RO_DEVNODE is a bit mask, ...

<snip>

> diff --git a/include/media/v4l2-dev.h b/include/media/v4l2-dev.h
> index 48531e57cc5a..029873a338f2 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_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_RO_DEVNODE		= 3,

... then V4L2_FL_RO_DEVNODE should rather be equal to 4, than to (V4L2_FL_USES_V4L2_FH | V4L2_FL_QUIRK_INVERTED_CROP)

Thanks,
Andrey

>   };
>   
>   /* Priority helper functions */
> diff --git a/include/media/v4l2-device.h b/include/media/v4l2-device.h
> index e0b8f2602670..0df667ba9938 100644
> --- a/include/media/v4l2-device.h
> +++ b/include/media/v4l2-device.h
> @@ -183,6 +183,16 @@ void v4l2_device_unregister_subdev(struct v4l2_subdev *sd);
>   int __must_check
>   v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev);
>   
> +/**
> + * v4l2_device_register_ro_subdev_nodes - Registers read-only 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
> + */
> +int __must_check
> +v4l2_device_register_ro_subdev_nodes(struct v4l2_device *v4l2_dev);
> +
>   /**
>    * v4l2_subdev_notify - Sends a notification to v4l2_device.
>    *
>