Re: [PATCH 1/2] media: dvbdev: make dvb_class constant

[Ricardo B. Marliere]

Hi Hans!

On  8 Apr 11:47, Hans Verkuil wrote:
> On 05/03/2024 14:26, Ricardo B. Marliere wrote:
> > Since commit 43a7206b0963 ("driver core: class: make class_register() take
> > a const *"), the driver core allows for struct class to be in read-only
> > memory, so move the dvb_class structure to be declared at build time
> > placing it into read-only memory, instead of having to be dynamically
> > allocated at boot time.
> > 
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Suggested-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Ricardo B. Marliere <ricardo@xxxxxxxxxxxx>
> > ---
> >  drivers/media/dvb-core/dvbdev.c | 23 +++++++++++++----------
> >  1 file changed, 13 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/media/dvb-core/dvbdev.c b/drivers/media/dvb-core/dvbdev.c
> > index 733d0bc4b4cc..dcbf68b00240 100644
> > --- a/drivers/media/dvb-core/dvbdev.c
> > +++ b/drivers/media/dvb-core/dvbdev.c
> > @@ -78,7 +78,13 @@ static const u8 minor_type[] = {
> >  #define MAX_DVB_MINORS		(DVB_MAX_ADAPTERS * 64)
> >  #endif
> >  
> > -static struct class *dvb_class;
> > +static int dvb_uevent(const struct device *dev, struct kobj_uevent_env *env);
> > +static char *dvb_devnode(const struct device *dev, umode_t *mode);
> 
> Forward references are typically something you want to avoid.
> 
> Looking at the code, I think it makes sense to just move those two functions
> to just before this dvb_class.

Ack.

> 
> > +static const struct class dvb_class = {
> > +	.name = "dvb",
> > +	.dev_uevent = dvb_uevent,
> > +	.devnode = dvb_devnode,
> > +};
> >  
> >  static struct dvb_device *dvb_minors[MAX_DVB_MINORS];
> >  static DECLARE_RWSEM(minor_rwsem);
> 
> Also move the dvb_class (+ the two functions) to after this line. I think that's
> a more suitable place for this.

Ack.

> 
> > @@ -561,7 +567,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
> >  		return ret;
> >  	}
> >  
> > -	clsdev = device_create(dvb_class, adap->device,
> > +	clsdev = device_create(&dvb_class, adap->device,
> >  			       MKDEV(DVB_MAJOR, minor),
> >  			       dvbdev, "dvb%d.%s%d", adap->num, dnames[type], id);
> >  	if (IS_ERR(clsdev)) {
> > @@ -600,7 +606,7 @@ void dvb_remove_device(struct dvb_device *dvbdev)
> >  
> >  	dvb_media_device_free(dvbdev);
> >  
> > -	device_destroy(dvb_class, MKDEV(DVB_MAJOR, dvbdev->minor));
> > +	device_destroy(&dvb_class, MKDEV(DVB_MAJOR, dvbdev->minor));
> >  
> >  	list_del(&dvbdev->list_head);
> >  }
> > @@ -1096,13 +1102,10 @@ static int __init init_dvbdev(void)
> >  		goto error;
> >  	}
> >  
> > -	dvb_class = class_create("dvb");
> > -	if (IS_ERR(dvb_class)) {
> > -		retval = PTR_ERR(dvb_class);
> > +	retval = class_register(&dvb_class);
> > +	if (retval != 0)
> 
> This can just be 'if (retval)'.

But then it would be on a different style than the rest of the function:

static int __init init_dvbdev(void)
{
	int retval;
	dev_t dev = MKDEV(DVB_MAJOR, 0);

	retval = register_chrdev_region(dev, MAX_DVB_MINORS, "DVB");
	if (retval != 0) {
		pr_err("dvb-core: unable to get major %d\n", DVB_MAJOR);
		return retval;
	}

	cdev_init(&dvb_device_cdev, &dvb_device_fops);
	retval = cdev_add(&dvb_device_cdev, dev, MAX_DVB_MINORS);
	if (retval != 0) {
		pr_err("dvb-core: unable register character device\n");
		goto error;
	}

	retval = class_register(&dvb_class);
	if (retval != 0)
		goto error;

	return 0;

error:
	cdev_del(&dvb_device_cdev);
	unregister_chrdev_region(dev, MAX_DVB_MINORS);
	return retval;
}


> 
> >  		goto error;
> > -	}
> > -	dvb_class->dev_uevent = dvb_uevent;
> > -	dvb_class->devnode = dvb_devnode;
> > +
> >  	return 0;
> >  
> >  error:
> > @@ -1115,7 +1118,7 @@ static void __exit exit_dvbdev(void)
> >  {
> >  	struct dvbdevfops_node *node, *next;
> >  
> > -	class_destroy(dvb_class);
> > +	class_unregister(&dvb_class);
> >  	cdev_del(&dvb_device_cdev);
> >  	unregister_chrdev_region(MKDEV(DVB_MAJOR, 0), MAX_DVB_MINORS);
> >  
> > 
> 
> Regards,
> 
> 	Hans