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Subject: Re: [PATCH v2 4/6] media: uvcvideo: set error_idx to count on EACCESS
To:     Ricardo Ribalda <ribalda@chromium.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Tomasz Figa <tfiga@chromium.org>, linux-media@vger.kernel.org,
        linux-kernel@vger.kernel.org, senozhatsky@chromium.org
References: <20210311221946.1319924-1-ribalda@chromium.org>
 <20210311221946.1319924-5-ribalda@chromium.org>
From:   Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <e5860193-a672-96b8-9a40-5f6d77dd4783@xs4all.nl>
Date:   Fri, 12 Mar 2021 08:14:13 +0100
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On 11/03/2021 23:19, Ricardo Ribalda wrote:
> According to the doc:
> The, in hindsight quite poor, solution for that is to set error_idx to
> count if the validation failed.

I think this needs a bit more explanation. How about this:

"If an error is found when validating the list of controls passed with
VIDIOC_G_EXT_CTRLS, then error_idx shall be set to ctrls->count to indicate
to userspace that no actual hardware was touched.

It would have been much nicer of course if error_idx could point to the
control index that failed the validation, but sadly that's not how the
API was designed."

> 
> Fixes v4l2-compliance:
> Control ioctls (Input 0):
>                 fail: v4l2-test-controls.cpp(645): invalid error index write only control
>         test VIDIOC_G/S/TRY_EXT_CTRLS: FAIL
> 
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

After improving the commit log you can add my:

Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Thanks!

	Hans

> ---
>  drivers/media/usb/uvc/uvc_v4l2.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 157310c0ca87..36eb48622d48 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -1073,7 +1073,8 @@ static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
>  		ret = uvc_ctrl_get(chain, ctrl);
>  		if (ret < 0) {
>  			uvc_ctrl_rollback(handle);
> -			ctrls->error_idx = i;
> +			ctrls->error_idx = (ret == -EACCES) ?
> +						ctrls->count : i;
>  			return ret;
>  		}
>  	}
>