On Wed, Feb 19, 2020 at 10:52:38AM +0800, Tiwei Bie wrote:
> > > +static int __init vhost_vdpa_init(void)
> > > +{
> > > + int r;
> > > +
> > > + idr_init(&vhost_vdpa.idr);
> > > + mutex_init(&vhost_vdpa.mutex);
> > > + init_waitqueue_head(&vhost_vdpa.release_q);
> > > +
> > > + /* /dev/vhost-vdpa/$vdpa_device_index */
> > > + vhost_vdpa.class = class_create(THIS_MODULE, "vhost-vdpa");
> > > + if (IS_ERR(vhost_vdpa.class)) {
> > > + r = PTR_ERR(vhost_vdpa.class);
> > > + goto err_class;
> > > + }
> > > +
> > > + vhost_vdpa.class->devnode = vhost_vdpa_devnode;
> > > +
> > > + r = alloc_chrdev_region(&vhost_vdpa.devt, 0, MINORMASK + 1,
> > > + "vhost-vdpa");
> > > + if (r)
> > > + goto err_alloc_chrdev;
> > > +
> > > + cdev_init(&vhost_vdpa.cdev, &vhost_vdpa_fops);
> > > + r = cdev_add(&vhost_vdpa.cdev, vhost_vdpa.devt, MINORMASK + 1);
> > > + if (r)
> > > + goto err_cdev_add;
> >
> > It is very strange, is the intention to create a single global char
> > dev?
>
> No. It's to create a per-vdpa char dev named
> vhost-vdpa/$vdpa_device_index in dev.
>
> I followed the code in VFIO which creates char dev
> vfio/$GROUP dynamically, e.g.:
>
> https://github.com/torvalds/linux/blob/b1da3acc781c/drivers/vfio/vfio.c#L2164-L2180
> https://github.com/torvalds/linux/blob/b1da3acc781c/drivers/vfio/vfio.c#L373-L387
> https://github.com/torvalds/linux/blob/b1da3acc781c/drivers/vfio/vfio.c#L1553
>
> Is it something unwanted?
Yes it is unwanted. This is some special pattern for vfio's unique
needs.
Since this has a struct device for each char dev instance please use
the normal cdev_device_add() driven pattern here, or justify why it
needs to be special like this.
Jason
