linux-kernel - RE: [PATCH v3 15/15] vfio: Add struct device to vfio

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Date:   Thu, 22 Sep 2022 05:18:34 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     Alex Williamson <alex.williamson@...hat.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Eric Farman <farman@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>,
        "Peter Oberparleiter" <oberpar@...ux.ibm.com>,
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        "Cornelia Huck" <cohuck@...hat.com>,
        Longfang Liu <liulongfang@...wei.com>,
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        Yishai Hadas <yishaih@...dia.com>,
        Eric Auger <eric.auger@...hat.com>,
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        Leon Romanovsky <leon@...nel.org>,
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        Christoph Hellwig <hch@...radead.org>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
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        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>
Subject: RE: [PATCH v3 15/15] vfio: Add struct device to vfio_device

> From: Jason Gunthorpe <jgg@...pe.ca>
> Sent: Thursday, September 22, 2022 12:10 AM
> 
> On Tue, Sep 20, 2022 at 10:55:40PM +0000, Tian, Kevin wrote:
> > > From: Alex Williamson <alex.williamson@...hat.com>
> > > Sent: Wednesday, September 21, 2022 4:27 AM
> > >
> > > On Fri,  9 Sep 2022 18:22:47 +0800
> > > Kevin Tian <kevin.tian@...el.com> wrote:
> > >
> > > > From: Yi Liu <yi.l.liu@...el.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?

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 probably
clearer, which is what I understood from your earlier suggestion.

> 
> 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.
> 

This is a good news.