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

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Date:   Wed, 29 Sep 2021 05:30:26 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     David Gibson <david@...son.dropbear.id.au>,
        "Liu, Yi L" <yi.l.liu@...el.com>
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Subject: RE: [RFC 03/20] vfio: Add vfio_[un]register_device()

> From: David Gibson <david@...son.dropbear.id.au>
> Sent: Wednesday, September 29, 2021 10:44 AM
> 
> > One alternative option is to arrange device nodes in sub-directories based
> > on the device type. But doing so also adds one trouble to userspace. The
> > current vfio uAPI is designed to have the user query device type via
> > VFIO_DEVICE_GET_INFO after opening the device. With this option the user
> > instead needs to figure out the device type before opening the device, to
> > identify the sub-directory.
> 
> Wouldn't this be up to the operator / configuration, rather than the
> actual software though?  I would assume that typically the VFIO
> program would be pointed at a specific vfio device node file to use,
> e.g.
> 	my-vfio-prog -d /dev/vfio/pci/0000:0a:03.1
> 
> Or more generally, if you're expecting userspace to know a name in a
> uniqu pattern, they can equally well know a "type/name" pair.
> 

You are correct. Currently:

-device, vfio-pci,host=DDDD:BB:DD.F
-device, vfio-pci,sysfdev=/sys/bus/pci/devices/ DDDD:BB:DD.F
-device, vfio-platform,sysdev=/sys/bus/platform/devices/PNP0103:00

above is definitely type/name information to find the related node. 

Actually even for Jason's proposal we still need such information to
identify the sysfs path.

Then I feel type-based sub-directory does work. Adding another link
to sysfs sounds unnecessary now. But I'm not sure whether we still
want to create /dev/vfio/devices/vfio0 thing and related udev rule
thing that you pointed out in another mail.

Jason?

Thanks
Kevin