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Re: [Qemu-devel] RFC: vfio / device assignment -- layout of device fd fi

From: Scott Wood
Subject: Re: [Qemu-devel] RFC: vfio / device assignment -- layout of device fd files
Date: Thu, 1 Sep 2011 15:26:01 -0500
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On 09/01/2011 03:00 PM, Michael S. Tsirkin wrote:
> That's a very rich interface, and easy to get wrong.
> AFAIK the only reason vfio uses read/write for PCI was to avoid inventing
> a custom interface. But if you do, it looks like a set of ioctls would
> be much easier? You can even fit the existing uio infrastructure if you like.

How would it be easier than producing/parsing a static data structure?
What would it look like?

> Here's another idea:  all the information is likely already available
> in sysfs.

The only major thing that is likely available elsewhere is PCI config
space, and that was not new to this proposal.

Most other material is specifically related to the vfio/dtio interface
(e.g. offsets into the file handle, arguments to the "get irq fd" ioctl,
mapping of dtio regions/interrupts to device tree nodes), and could not
be "useful to more than just vfio".

> A way to query where the device is in sysfs
> would give you *a ton* of information, including the type etc,

For PCI, the user has domain/bus/dev/fn which should be sufficient to
find that, if desired.  For device-tree devices, there's a device tree
path provided for each region/interrupt.


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