linux-kernel - Re: [PATCH v3 07/33] drm/vkms: Introduce configfs for plane name

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Message-Id: <DF5JW5Z5K9YE.2PCYFIFFMT6G6@bootlin.com>
Date: Tue, 23 Dec 2025 12:14:08 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Louis Chauvet" <louis.chauvet@...tlin.com>, "Haneen Mohammed"
 <hamohammed.sa@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Melissa Wen"
 <melissa.srw@...il.com>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "David Airlie"
 <airlied@...il.com>, <jose.exposito89@...il.com>, "Jonathan Corbet"
 <corbet@....net>
Cc: <victoria@...tem76.com>, <sebastian.wick@...hat.com>,
 <thomas.petazzoni@...tlin.com>, <dri-devel@...ts.freedesktop.org>,
 <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v3 07/33] drm/vkms: Introduce configfs for plane name

On Mon Dec 22, 2025 at 11:11 AM CET, Louis Chauvet wrote:
> Planes can have name, create a plane attribute to configure it. Currently
> plane name is mainly used in logs.
>
> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> ---
>  Documentation/ABI/testing/configfs-vkms |  6 +++++
>  Documentation/gpu/vkms.rst              |  3 ++-
>  drivers/gpu/drm/vkms/vkms_configfs.c    | 43 +++++++++++++++++++++++++++++++++
>  3 files changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
> index 0beaa25f30ba..6fe375d1636f 100644
> --- a/Documentation/ABI/testing/configfs-vkms
> +++ b/Documentation/ABI/testing/configfs-vkms
> @@ -103,6 +103,12 @@ Description:
>          Plane type. Possible values: 0 - overlay, 1 - primary,
>          2 - cursor.
>
> +What:		/sys/kernel/config/vkms/<device>/planes/<plane>/name
> +Date:		Nov 2025
> +Contact:	dri-devel@...ts.freedesktop.org
> +Description:
> +        Name of the plane.
> +
>  What:		/sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
>  Date:		Nov 2025
>  Contact:	dri-devel@...ts.freedesktop.org
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index 1e79e62a6bc4..79f1185d8645 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,10 +87,11 @@ Start by creating one or more planes::
>
>    sudo mkdir /config/vkms/my-vkms/planes/plane0
>
> -Planes have 1 configurable attribute:
> +Planes have 2 configurable attributes:
>
>  - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
>    exposed by the "type" property of a plane)
> +- name: Name of the plane. Allowed characters are [A-Za-z1-9_-]
>
>  Continue by creating one or more CRTCs::
>
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
> index 506666e21c91..989788042191 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -324,10 +324,53 @@ static ssize_t plane_type_store(struct config_item *item, const char *page,
>  	return (ssize_t)count;
>  }
>
> +static ssize_t plane_name_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +	const char *name;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	scoped_guard(mutex, &plane->dev->lock)
> +		name = vkms_config_plane_get_name(plane->config);

vkms_config_plane_get_name() returns a pointer to the name string, not a
copy. Unless I'm missing something, that string might be freed before the
next lines, where it is used:

> +
> +	if (name)
> +		return sprintf(page, "%s\n", name);
> +	return sprintf(page, "\n");

So for safety the above 3 lines whould go inside the scoped_guard().

> +}
> +
> +static ssize_t plane_name_store(struct config_item *item, const char *page,
> +				size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +	size_t str_len;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	// strspn is not lenght-protected, ensure that page is a null-terminated string.
> +	str_len = strnlen(page, count);
> +	if (str_len >= count)
> +		return -EINVAL;
> +
> +	if (strspn(page, "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-") != count - 1)
> +		return -EINVAL;

I see you effor to make this as clean as possible, thanks. Still this is a
tad ugly, and should be moved to some common place at some point IMO. For
now it's fine, but if you need to add more user-passed strings, that could
be the moment to move this code.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com