Re: [PATCH v2] mm/hmm/test: simplify hmm test code: use miscdevice instead of char dev

[Mika Penttilä]

On 17.3.2022 16.15, Jason Gunthorpe wrote:
> On Thu, Mar 17, 2022 at 08:58:52AM +0200, Mika Penttilä wrote:
> > @@ -1225,7 +1232,11 @@ static int dmirror_device_init(struct dmirror_device
> > *mdevice, int id)
> >
> >          cdev_init(&mdevice->cdevice, &dmirror_fops);
> >          mdevice->cdevice.owner = THIS_MODULE;
> > -       ret = cdev_add(&mdevice->cdevice, dev, 1);
> > +       device_initialize(&mdevice->device);
> > +       dev_set_name(&mdevice->device, "%s", dmirror_device_names[id]);
> > +       mdevice->device.devt = dev;
> > +
> > +       ret = cdev_device_add(&mdevice->cdevice, &mdevice->device);
> >          if (ret)
> >                  return ret;
>
> Right, miscdev isn't that helpful in the end..
>
> Jason

To wrap up, I could send a v3 formal patch with either this cdev way or 
the miscdev way.. Both eliminate the user space /proc/devices parsing 
and mknod'ing. Jason brought up concerns using miscdevice like this, 
although for this case it works correctly. miscdevice also provides a 
little more cleanup and simpler code, but the difference is not huge. So 
what do people prefer?

Thanks,
Mika