Re: [PATCH 4/6] drm: Change drm_class from pointer to const struct class

[Heiner Kallweit <hkallweit1@gmail.com>]

On 22.09.2024 17:11, Dmitry Baryshkov wrote:
> On Sun, Sep 08, 2024 at 02:11:25PM GMT, Heiner Kallweit wrote:
>> Define class drm statically and constify it. This ensure that no user
>> of the exported struct class can tamper with it.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>>  drivers/gpu/drm/drm_internal.h       |  2 +-
>>  drivers/gpu/drm/drm_privacy_screen.c |  2 +-
>>  drivers/gpu/drm/drm_sysfs.c          | 32 ++++++++++++++--------------
>>  3 files changed, 18 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
>> index 1705bfc90..6e0df44b6 100644
>> --- a/drivers/gpu/drm/drm_internal.h
>> +++ b/drivers/gpu/drm/drm_internal.h
>> @@ -139,7 +139,7 @@ bool drm_master_internal_acquire(struct drm_device *dev);
>>  void drm_master_internal_release(struct drm_device *dev);
>>  
>>  /* drm_sysfs.c */
>> -extern struct class *drm_class;
>> +extern const struct class drm_class;
>>  
>>  int drm_sysfs_init(void);
>>  void drm_sysfs_destroy(void);
>> diff --git a/drivers/gpu/drm/drm_privacy_screen.c b/drivers/gpu/drm/drm_privacy_screen.c
>> index 6cc39e307..2fbd24ba5 100644
>> --- a/drivers/gpu/drm/drm_privacy_screen.c
>> +++ b/drivers/gpu/drm/drm_privacy_screen.c
>> @@ -401,7 +401,7 @@ struct drm_privacy_screen *drm_privacy_screen_register(
>>  	mutex_init(&priv->lock);
>>  	BLOCKING_INIT_NOTIFIER_HEAD(&priv->notifier_head);
>>  
>> -	priv->dev.class = drm_class;
>> +	priv->dev.class = &drm_class;
>>  	priv->dev.type = &drm_privacy_screen_type;
>>  	priv->dev.parent = parent;
>>  	priv->dev.release = drm_privacy_screen_device_release;
>> diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
>> index f8577043e..f443f9a76 100644
>> --- a/drivers/gpu/drm/drm_sysfs.c
>> +++ b/drivers/gpu/drm/drm_sysfs.c
>> @@ -58,7 +58,15 @@ static struct device_type drm_sysfs_device_connector = {
>>  	.name = "drm_connector",
>>  };
>>  
>> -struct class *drm_class;
>> +static char *drm_devnode(const struct device *dev, umode_t *mode)
>> +{
>> +	return kasprintf(GFP_KERNEL, "dri/%s", dev_name(dev));
>> +}
>> +
>> +const struct class drm_class = {
>> +	.name = "drm",
>> +	.devnode = drm_devnode,
>> +};
>>  
>>  #ifdef CONFIG_ACPI
>>  static bool drm_connector_acpi_bus_match(struct device *dev)
>> @@ -93,11 +101,6 @@ static void drm_sysfs_acpi_register(void) { }
>>  static void drm_sysfs_acpi_unregister(void) { }
>>  #endif
>>  
>> -static char *drm_devnode(const struct device *dev, umode_t *mode)
>> -{
>> -	return kasprintf(GFP_KERNEL, "dri/%s", dev_name(dev));
>> -}
>> -
> 
> Please keep this function in place and move drm_class declarattion next
> to it. It simplifies reviewing the code.
> 
>>  static int typec_connector_bind(struct device *dev,
>>  				struct device *typec_connector, void *data)
>>  {
>> @@ -138,14 +141,12 @@ static const struct component_ops typec_connector_ops = {
>>   */
>>  int drm_sysfs_init(void)
>>  {
>> -	drm_class = class_create("drm");
>> -	if (IS_ERR(drm_class))
>> -		return PTR_ERR(drm_class);
>> +	int ret = class_register(&drm_class);
>>  
>> -	drm_class->devnode = drm_devnode;
>> +	if (!ret)
>> +		drm_sysfs_acpi_register();
>>  
>> -	drm_sysfs_acpi_register();
>> -	return 0;
>> +	return ret;
>>  }
>>  
>>  /**
>> @@ -156,8 +157,7 @@ int drm_sysfs_init(void)
>>  void drm_sysfs_destroy(void)
>>  {
>>  	drm_sysfs_acpi_unregister();
>> -	class_destroy(drm_class);
>> -	drm_class = NULL;
>> +	class_unregister(&drm_class);
> 
> This code makes me wonder: can we define static classes in unloadable
> modules? What happens if userspace holds the reference on the class in
> sysfs, while we remove the module ?
> 
I'm not sure, just saw that this isn't an unusual scenario.
Let's ask the drivers/base maintainers.
+Greg/Rafael

>>  }
>>  
>>  static void drm_sysfs_release(struct device *dev)
>> @@ -337,7 +337,7 @@ int drm_sysfs_connector_add(struct drm_connector *connector)
>>  		return -ENOMEM;
>>  
>>  	device_initialize(kdev);
>> -	kdev->class = drm_class;
>> +	kdev->class = &drm_class;
>>  	kdev->type = &drm_sysfs_device_connector;
>>  	kdev->parent = dev->primary->kdev;
>>  	kdev->groups = connector_dev_groups;
>> @@ -516,7 +516,7 @@ struct device *drm_sysfs_minor_alloc(struct drm_minor *minor)
>>  			minor_str = "card%d";
>>  
>>  		kdev->devt = MKDEV(DRM_MAJOR, minor->index);
>> -		kdev->class = drm_class;
>> +		kdev->class = &drm_class;
>>  		kdev->type = &drm_sysfs_device_minor;
>>  	}
>>  
>> -- 
>> 2.46.0
>>
>>
>