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

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Date:   Wed, 31 Aug 2022 11:15:12 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        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>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Tony Krowiak <akrowiak@...ux.ibm.com>,
        Jason Herne <jjherne@...ux.ibm.com>,
        Harald Freudenberger <freude@...ux.ibm.com>,
        Diana Craciun <diana.craciun@....nxp.com>,
        "Cornelia Huck" <cohuck@...hat.com>,
        Longfang Liu <liulongfang@...wei.com>,
        "Shameer Kolothum" <shameerali.kolothum.thodi@...wei.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Eric Auger <eric.auger@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Abhishek Sahu <abhsahu@...dia.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>
Subject: Re: [PATCH 15/15] vfio: Add struct device to vfio_device

On Wed, 31 Aug 2022 06:10:51 +0000
"Tian, Kevin" <kevin.tian@...el.com> wrote:

> > From: Jason Gunthorpe <jgg@...pe.ca>
> > Sent: Wednesday, August 31, 2022 7:53 AM
> > 
> > On Tue, Aug 30, 2022 at 04:18:38PM -0600, Alex Williamson wrote:  
> > > On Sun, 28 Aug 2022 01:10:37 +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.  
> > >
> > > Shall we start Documentation/ABI/testing/vfio-dev now?  Thanks.  
> > 
> > I always thought that was something to use when adding new custom
> > sysfs attributes?
> > 
> > Here we are just creating a standard struct device with its standard
> > sysfs?
> >   
> 
> There is nothing special for vfio-dev/vfioX. But from pci device p.o.v
> this does introduce a custom node in the directory, which is probably
> what Alex referred to?

Yup, but not just for pci, we're adding a node into the device
directory for any device bound to vfio.

> Anyway if required following can be introduced:
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-vfio-dev b/Documentation/ABI/testing/sysfs-devices-vfio-dev
> new file mode 100644
> index 000000000000..dfe8baaf1ccb
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-devices-vfio-dev
> @@ -0,0 +1,8 @@
> +What:		 /sys/.../<device>/vfio-dev/vfioX/
> +Date:		 September 2022
> +Contact:	 Yi Liu <yi.l.liu@...el.com>
> +Description:
> +		 This directory is created when the device is bound to a
> +		 vfio driver. The layout under this directory matches what
> +		 exists for a standard 'struct device'. 'X' is a random
> +		 number marking this device in vfio.

It's not really random, it's a unique index.  Seems like a good
starting point.

> 
> At the start I thought it might make more sense to add it into an
> existing vfio ABI file. But looks it doesn't exist.
> 
> Curious why nobody asked for ABI doc for /dev/vfio/vfio, /sys/class/vfio, etc...

Oversight, there should probably be a sysfs-class-vfio file.  Thanks,

Alex