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Message-ID: <1426847799.32097.66.camel@nilsson.home.kraxel.org>
Subject: Re: [PATCH 1/1] Add virtio-input driver.
From: Gerd Hoffmann <kraxel@redhat.com>
To: David Herrmann <dh.herrmann@gmail.com>
Cc: virtio-dev@lists.oasis-open.org, virtualization@lists.linux-foundation.org,
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Date: Fri, 20 Mar 2015 11:36:39 +0100
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  Hi,

> > There will also be pass-through support, i.e. qemu
> > opening /dev/input/event<nr> and forwarding everything to the guest.
> > How should that be handled best?  Copy all four from the host?  Even
> > though the bustype is BUS_USB?  Not sure this actually improves things
> > because the guest can match the device, or whenever this confuses apps
> > due to BUS_USB being applied to virtio devices ...
> 
> Lemme give an example: We have databases in user-space, that allow
> applications to figure out the mouse DPI values of a device. Those
> databases match on all four, bus+vid+pid+ver (sometimes even more,
> like name and dmi). If one of those is not forwarded, it will not be
> detected.

Ok, so forward as much as possible.

> I'd like to see all four forwarded from the host. I'd be fine with
> "bus" being set to VIRTUAL, but I'm not sure why that would be a good
> thing to do?

I think for the emulated devices it's fine to use VIRTUAL.

For the passthrough case suspected we could confuse apps because ->phys
points to a virtio device whereas ->type says "I'm usb".

But at least the device database probably doesn't care much about the
physical path I guess, because the mouse is the same no matter which usb
port I plug it in, correct?

cheers,
  Gerd