linux-kernel - Re: [PATCH v4 1/3] media: v4l2-dev.c: Add Meta: to the name of metadata devices

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Date:   Tue, 6 Dec 2022 00:03:07 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Yunke Cao <yunkec@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-media@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] media: v4l2-dev.c: Add Meta: to the name of
 metadata devices

Hi Ricardo,

Thank you for the patch.

On Fri, Dec 02, 2022 at 06:08:17PM +0100, Ricardo Ribalda wrote:
> Devices with Metadata output (like uvc), create two video devices, one
> for the data itself and another one for the metadata.
> 
> Add a "Meta: " to the beginning of the device name, as suggested by Mauro,
> to avoid having multiple devices with the same name.
> 
> Fixes v4l2-compliance:
> Media Controller ioctls:
>      fail: v4l2-test-media.cpp(205): v2_entity_names_set.find(key) != v2_entity_names_set.end()
>    test MEDIA_IOC_G_TOPOLOGY: FAIL
>      fail: v4l2-test-media.cpp(394): num_data_links != num_links
>    test MEDIA_IOC_ENUM_ENTITIES/LINKS: FAIL
> 
> Suggested-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/v4l2-core/v4l2-dev.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> index 397d553177fa..5c2c9ebb6b96 100644
> --- a/drivers/media/v4l2-core/v4l2-dev.c
> +++ b/drivers/media/v4l2-core/v4l2-dev.c
> @@ -901,6 +901,15 @@ int __video_register_device(struct video_device *vdev,
>  	if (WARN_ON(type != VFL_TYPE_SUBDEV && !vdev->device_caps))
>  		return -EINVAL;
>  
> +	/* Add Meta: to metadata device names */
> +	if (vdev->device_caps &
> +	    (V4L2_CAP_META_CAPTURE | V4L2_CAP_META_OUTPUT)) {
> +		char aux[sizeof(vdev->name)];
> +
> +		snprintf(aux, sizeof(aux), "Meta: %s", vdev->name);

This will break userspace I'm afraid. libcamera looks up video devices
by entity names for multiple platforms. I wouldn't be surprised if other
userspace applications did something similar.

> +		strscpy(vdev->name, aux, sizeof(aux));
> +	}
> +
>  	/* v4l2_fh support */
>  	spin_lock_init(&vdev->fh_lock);
>  	INIT_LIST_HEAD(&vdev->fh_list);
> 

-- 
Regards,

Laurent Pinchart