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

[Jacopo Mondi <jacopo@jmondi.org>]

Hi Laurent,

On Wed, Mar 25, 2020 at 11:45:36PM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
>
> Thank you for the patch.
>
> On Tue, Mar 24, 2020 at 09:28:42PM +0100, 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;
>
> As Andrey pointed out, this should be BIT(V4L2_FL_RO_DEVNODE).
>

the rest of the v4l2 core seems to be use set_bit()/test_bit() when
handling V4L2_FL_ (which, my bad, I rarely encoutered compared to the
to me more canonical BIT() combined with bitops).

I would then go for them then

> >  		err = __video_register_device(vdev, VFL_TYPE_SUBDEV, -1, 1,
> >  					      sd->owner);
> >  		if (err < 0) {
> > @@ -254,8 +257,19 @@ int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
> >
> >  	return err;
> >  }
> > +
> > +int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
> > +{
> > +	return __v4l2_device_register_subdev_nodes(v4l2_dev, false);
> > +}
> >  EXPORT_SYMBOL_GPL(v4l2_device_register_subdev_nodes);
> >
> > +int v4l2_device_register_ro_subdev_nodes(struct v4l2_device *v4l2_dev)
> > +{
> > +	return __v4l2_device_register_subdev_nodes(v4l2_dev, true);
> > +}
> > +EXPORT_SYMBOL_GPL(v4l2_device_register_ro_subdev_nodes);
>
> I would export __v4l2_device_register_subdev_nodes and implement these
> two functions as static inline in include/media/v4l2-device.h.
>

Good point we could save a function call.

> > +
> >  void v4l2_device_unregister_subdev(struct v4l2_subdev *sd)
> >  {
> >  	struct v4l2_device *v4l2_dev;
> > diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> > index f725cd9b66b9..9247ee6c293f 100644
> > --- a/drivers/media/v4l2-core/v4l2-subdev.c
> > +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> > @@ -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);
>
> Same here, BIT(V4L2_FL_RO_DEVNODE).
>
> I would name the variable ro_api to emphasize this is not about the
> device node being read-only (in the sense of POSIX file permissions).
>

Ack, even if I would like ro_subdev a bit more. Anyway bikesheeding on
variable names, ro_api is fine.

Thanks
  j


> >  	int rval;
> >  #endif
> >
> > @@ -453,6 +454,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
> >  	case VIDIOC_SUBDEV_S_FMT: {
> >  		struct v4l2_subdev_format *format = arg;
> >
> > +		if (format->which != V4L2_SUBDEV_FORMAT_TRY && ro_devnode)
> > +			return -EPERM;
> > +
> >  		memset(format->reserved, 0, sizeof(format->reserved));
> >  		memset(format->format.reserved, 0, sizeof(format->format.reserved));
> >  		return v4l2_subdev_call(sd, pad, set_fmt, subdev_fh->pad, format);
> > @@ -480,6 +484,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
> >  		struct v4l2_subdev_crop *crop = arg;
> >  		struct v4l2_subdev_selection sel;
> >
> > +		if (crop->which != V4L2_SUBDEV_FORMAT_TRY && ro_devnode)
> > +			return -EPERM;
> > +
> >  		memset(crop->reserved, 0, sizeof(crop->reserved));
> >  		memset(&sel, 0, sizeof(sel));
> >  		sel.which = crop->which;
> > @@ -521,6 +528,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
> >  	case VIDIOC_SUBDEV_S_FRAME_INTERVAL: {
> >  		struct v4l2_subdev_frame_interval *fi = arg;
> >
> > +		if (ro_devnode)
> > +			return -EPERM;
> > +
> >  		memset(fi->reserved, 0, sizeof(fi->reserved));
> >  		return v4l2_subdev_call(sd, video, s_frame_interval, arg);
> >  	}
> > @@ -544,6 +554,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
> >  	case VIDIOC_SUBDEV_S_SELECTION: {
> >  		struct v4l2_subdev_selection *sel = arg;
> >
> > +		if (sel->which != V4L2_SUBDEV_FORMAT_TRY && ro_devnode)
> > +			return -EPERM;
> > +
> >  		memset(sel->reserved, 0, sizeof(sel->reserved));
> >  		return v4l2_subdev_call(
> >  			sd, pad, set_selection, subdev_fh->pad, sel);
> > @@ -580,6 +593,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
> >  		return v4l2_subdev_call(sd, video, g_dv_timings, arg);
> >
> >  	case VIDIOC_SUBDEV_S_DV_TIMINGS:
> > +		if (ro_devnode)
> > +			return -EPERM;
> > +
> >  		return v4l2_subdev_call(sd, video, s_dv_timings, arg);
> >
> >  	case VIDIOC_SUBDEV_G_STD:
> > @@ -588,6 +604,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
> >  	case VIDIOC_SUBDEV_S_STD: {
> >  		v4l2_std_id *std = arg;
> >
> > +		if (ro_devnode)
> > +			return -EPERM;
> > +
> >  		return v4l2_subdev_call(sd, video, s_std, *std);
> >  	}
> >
> > 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,
> >  };
> >
> >  /* 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.
> >   *
>
> --
> Regards,
>
> Laurent Pinchart