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From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Jason Gunthorpe <jgg@ziepe.ca>
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Subject: RE: [PATCH v3 15/15] vfio: Add struct device to vfio_device
Thread-Topic: [PATCH v3 15/15] vfio: Add struct device to vfio_device
Thread-Index: AQHYw/kWx/ZcHkFOHU+t8x4U9WUM+a3o1qGAgAAo6+CAASHXgIAA2nvQ
Date:   Thu, 22 Sep 2022 05:18:34 +0000
Message-ID: <BN9PR11MB527652CF1116B185E4311FDF8C4E9@BN9PR11MB5276.namprd11.prod.outlook.com>
References: <20220909102247.67324-1-kevin.tian@intel.com>
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 <20220920142639.29b1bdc2.alex.williamson@redhat.com>
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> From: Jason Gunthorpe <jgg@ziepe.ca>
> Sent: Thursday, September 22, 2022 12:10 AM
>=20
> On Tue, Sep 20, 2022 at 10:55:40PM +0000, Tian, Kevin wrote:
> > > From: Alex Williamson <alex.williamson@redhat.com>
> > > Sent: Wednesday, September 21, 2022 4:27 AM
> > >
> > > On Fri,  9 Sep 2022 18:22:47 +0800
> > > Kevin Tian <kevin.tian@intel.com> wrote:
> > >
> > > > From: Yi Liu <yi.l.liu@intel.com>
> > > >
> > > > and replace kref. With it a 'vfio-dev/vfioX' node is created under =
the
> > > > sysfs path of the parent, indicating the device is bound to a vfio
> > > > driver, e.g.:
> > > >
> > > > /sys/devices/pci0000\:6f/0000\:6f\:01.0/vfio-dev/vfio0
> > > >
> > > > It is also a preparatory step toward adding cdev for supporting fut=
ure
> > > > device-oriented uAPI.
> > > >
> > > > Add Documentation/ABI/testing/sysfs-devices-vfio-dev.
> > > >
> > > > Also take this chance to rename chardev 'vfio' to 'vfio-group' in
> > > > /proc/devices.
> > >
> > > What's the risk/reward here, is this just more aesthetically pleasing
> > > symmetry vs 'vfio-dev'?  The char major number to name association in
> > > /proc/devices seems pretty obscure, but what due diligence have we
> done
> > > to make sure this doesn't break anyone?  Thanks,
> >
> > I'm not sure whether the content of /proc/devices is considered as ABI.
> >
> > @Jason?
>=20
> Ah, I've forgotten why we got here - didn't we have a naming conflict
> with the new stuff that is being introduced?

No, we don't have. There is no new char dev introduced in this series.

Later when device cdev is added a new device major will be allocated for
'vfio-dev'. It's at that time renaming existing 'vfio' to 'vfio-group' is p=
robably
clearer, which is what I understood from your earlier suggestion.

>=20
> ABI wise it is not a problem unless there is a real user, I'm not
> aware of anything scanning /proc, that has been obsoleted by sysfs a
> long time ago.
>=20

This is a good news.