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@bootlin.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@lists.freedesktop.org
+Description:
+        Name of the plane.
+
 What:		/sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
 Date:		Nov 2025
 Contact:	dri-devel@lists.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);
+
+	if (name)
+		return sprintf(page, "%s\n", name);
+	return sprintf(page, "\n");
+}
+
+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;
+
+	scoped_guard(mutex, &plane->dev->lock) {
+		if (plane->dev->enabled)
+			return -EBUSY;
+
+		vkms_config_plane_set_name(plane->config, page);
+	}
+
+	return (ssize_t)count;
+}
+
 CONFIGFS_ATTR(plane_, type);
+CONFIGFS_ATTR(plane_, name);
 
 static struct configfs_attribute *plane_item_attrs[] = {
 	&plane_attr_type,
+	&plane_attr_name,
 	NULL,
 };
 

-- 
2.51.2

Hey Louis,

On Mon, Dec 22, 2025 at 11:11:09AM +0100, 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@bootlin.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@lists.freedesktop.org
> +Description:
> +        Name of the plane.
> +
>  What:		/sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
>  Date:		Nov 2025
>  Contact:	dri-devel@lists.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);
> +
> +	if (name)
> +		return sprintf(page, "%s\n", name);
> +	return sprintf(page, "\n");
> +}
> +
> +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;

I made a very quick review of v3 and I'm sending the initial issues I found, but I'd need
to do a deeper review.

This check is preventing me to set the name. For example, running:

$ echo "planename" | sudo tee /sys/kernel/config/vkms/gpu1/planes/plane0/name

Fails because str_len = 10 and count = 10. Does the same happen on your side?

Jose

> +
> +	if (strspn(page, "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-") != count - 1)
> +		return -EINVAL;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		if (plane->dev->enabled)
> +			return -EBUSY;
> +
> +		vkms_config_plane_set_name(plane->config, page);
> +	}
> +
> +	return (ssize_t)count;
> +}
> +
>  CONFIGFS_ATTR(plane_, type);
> +CONFIGFS_ATTR(plane_, name);
>  
>  static struct configfs_attribute *plane_item_attrs[] = {
>  	&plane_attr_type,
> +	&plane_attr_name,
>  	NULL,
>  };
>  
> 
> -- 
> 2.51.2
>

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@bootlin.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@lists.freedesktop.org
> +Description:
> +        Name of the plane.
> +
>  What:		/sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
>  Date:		Nov 2025
>  Contact:	dri-devel@lists.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

On 12/23/25 12:14, Luca Ceresoli wrote:
> 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@bootlin.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@lists.freedesktop.org
>> +Description:
>> +        Name of the plane.
>> +
>>   What:		/sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
>>   Date:		Nov 2025
>>   Contact:	dri-devel@lists.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().

Good catch!

This also raised some questions on the whole locking synchronization 
between configfs / config / DRM core. I will work on this topic and 
maybe move the mutex / add a refcount to vkms_config.

>> +}
>> +
>> +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.

There are multiple "user strings" in this file (notably group names), 
but currently without limitation.

I can create a tiny helper and limit all user strings to a-zA-Z0-9_-
It will technically break the ABI, but I don't think this is a big issue.

Do you or José think this is a good idea? If so I can extract the helper 
for v4 and send a separate series to do the limitation on other strings.

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

On Mon, Dec 29, 2025 at 03:40:23PM +0100, Louis Chauvet wrote:
> 
> 
> On 12/23/25 12:14, Luca Ceresoli wrote:
> > 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@bootlin.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@lists.freedesktop.org
> > > +Description:
> > > +        Name of the plane.
> > > +
> > >   What:		/sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
> > >   Date:		Nov 2025
> > >   Contact:	dri-devel@lists.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().
> 
> Good catch!
> 
> This also raised some questions on the whole locking synchronization between
> configfs / config / DRM core. I will work on this topic and maybe move the
> mutex / add a refcount to vkms_config.
> 
> > > +}
> > > +
> > > +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.
> 
> There are multiple "user strings" in this file (notably group names), but
> currently without limitation.
> 
> I can create a tiny helper and limit all user strings to a-zA-Z0-9_-
> It will technically break the ABI, but I don't think this is a big issue.
> 
> Do you or José think this is a good idea? If so I can extract the helper for
> v4 and send a separate series to do the limitation on other strings.

From the top of my head, I think that at the moment the device name is the only
user facing string that is not limted in code? It is limited by the allowed
characters in filenames. But I might be forgetting other custom strings.

Technically, it'd be an ABI break... So, while I think it shouldn't be an issue,
I'd prefer to avoid breaking the ABI, but I leave the decision to you.

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