Re: [PATCH v3 15/15] vfio: Add struct device to vfio_device

From: Jason Gunthorpe <jgg@ziepe.ca>
To: "Tian, Kevin" <kevin.tian@intel.com>
Cc: Matthew Rosato <mjrosato@linux.ibm.com>,
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Subject: Re: [PATCH v3 15/15] vfio: Add struct device to vfio_device
Date: Wed, 21 Sep 2022 13:10:29 -0300	[thread overview]
Message-ID: <Yys3dZS5ZUByiXin@ziepe.ca> (raw)
In-Reply-To: <BN9PR11MB5276484952784F5E336814BD8C4C9@BN9PR11MB5276.namprd11.prod.outlook.com>

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 future
> > > 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?

Ah, I've forgotten why we got here - didn't we have a naming conflict
with the new stuff that is being introduced?

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.

Jason