linux-kernel - Re: [RFC 03/20] vfio: Add vfio_[un]register

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Date:   Wed, 22 Sep 2021 20:56:39 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
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Subject: Re: [RFC 03/20] vfio: Add vfio_[un]register_device()

On Wed, Sep 22, 2021 at 02:10:36PM -0600, Alex Williamson wrote:

> But why would we create vfio device interface files at all if they
> can't work?  I'm not really on board with creating a try-and-fail
> interface for a mechanism that cannot work for a given device.  The
> existence of the device interface should indicate that it's supported.

I'm a little worried about adding a struct device to vfio_device and
then making it optional.. That is a really weird situation.

I suppose you could create the sysfs presence in the struct device but
not create a cdev.

However, if we ever want to use the device fd for something else, like
querying the device driver capabilities or mode, (ie clean the
driver_api thing wrongly placed in mdev sysfs for instance), we are
blocked as the uAPI will be cdev == must support iommufd..

Jason