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Re: [Qemu-devel] [PATCH RFC] ps2: set the keybord output buffer size as

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] [PATCH RFC] ps2: set the keybord output buffer size as the same as kernel
Date: Wed, 23 Apr 2014 16:02:28 +0200


> > Completely separate question:  Have you figured what the root cause for
> > the bug is?  
> > While wading through the code I've figured the queue size
> > isn't (directly) exposed to the guest.  

> The process correspond with the above linux kernel code, i8042_flush(void).

So linux tries to flush the buffer, then is confused in case it can read
more than 16 bytes (which is the buffer size of real hardware) without
seeing the status register signaling that the buffer is empty.  So the
qemu internal buffer size is indirectly visible to the guest.


We could try sending the data to the guest in chunks, i.e. signal
"buffer empty", then set up a (short) timer when we'll go make it appear
to the guest as if new data arrived (which in reality just comes from
out large buffer).

Not that easy to do, as we should better avoid splitting messages in the

> > but for mouse events we
> > probably want keep some more space to buffer events ...
> >
> Maybe you are right, and I worry about it too. At present,
> but I haven't feel uncomfortable by VNC client then before.

Do you have a usb-tablet attached, for more comfortable absolute
coordinates?  If so, then the ps/2 mouse will not be used to deliver
events to the guest.

And as this is a pretty common setup we maybe should not worry too much
about the ps/2 mouse queue depth ...


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