linux-kernel - Re: [PATCHv3 5/6] media: uvcvideo: add UVC 1.5 ROI control

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Date:   Wed, 24 Mar 2021 11:31:06 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Ricardo Ribalda <ribalda@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv3 5/6] media: uvcvideo: add UVC 1.5 ROI control

On (21/03/24 11:14), Tomasz Figa wrote:
> > > > +static int uvc_ioctl_s_roi(struct file *file, void *fh,
> > > > +                          struct v4l2_selection *sel)
> > > > +{
> > > > +       struct uvc_fh *handle = fh;
> > > > +       struct uvc_streaming *stream = handle->stream;
> > > > +       struct uvc_roi_rect *roi;
> > > > +       int ret;
> > > > +
> > > > +       if (!validate_roi_bounds(stream, sel))
> > > > +               return -E2BIG;
> > >
> > > Not sure if this is the correct approach or if we should convert the
> > > value to the closest valid...
> >
> > Well, at this point we know that ROI rectangle dimensions are out of
> > sane value range. I'd rather tell user-space about integer overflow.
> 
> Adjusting the rectangle to something supported by the hardware is
> mentioned explicitly in the V4L2 API documentation and is what drivers
> have to implement. Returning an error on invalid value is not a
> correct behavior here (and similarly for many other operations, e.g.
> S_FMT).

Well, in this particular case we are talking about user-space that wants
to set ROI rectangle that is knowingly violates device's GET_MAX and
overflows UVC ROI rectangle u16 value range. That's a clear bug in user-space.
Do we want to pretend that user-space does the correct thing and fixup
stuff behind the scenes?

> > Looking for the closest ROI rectangle that suffice can be rather
> > tricky. It may sounds like we can just use BOUNDARIES_MAX, but this
> > is what Firmware D returns for GET_MAX
> >
> > ioctl(V4L2_SEL_TGT_ROI_BOUNDS_MAX)
> >
> >         0, 0, 65535, 65535
> 
> Perhaps the frame size would be the correct bounds?

I can check that.