Re: [Qemu-devel] [PATCH v2 1/6] qerror: add MAX_KEYCODES 16

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 15 Jun 2012 09:57:49 +0200
Gerd Hoffmann <kraxel@redhat.com> wrote:

>   Hi,
> 
> >> It seems we need to notice user when inputted keys are more than 16.
> > 
> > Hi Gerd,
> > 
> > When I use 'sendkey' command to send key-series to guest, some keyboard
> > events will be send. There is a limitation (16) that was introduced by this
> > old commit c8256f9d (without description). Do you know the reason?
> 
> Probably hardware limitation, ps/2 keyboards can buffer up to 16 keys IIRC.

Then the perfect thing to do would be to drop the MAX_KEYCODES check from
the sendkey command and move bounds checking down to the device emulation code.

However, this will require a bit of code churn if we do it for all devices,
and won't buy us much, as the most likely reason for the error is a client/user
trying to send too many keys in parallel to the guest, right?

If this is right, then I think that the best thing to do would be to drop the
MAX_KEYCODES check from the sendkey command and document that devices can drop
keys if too many of them are sent in parallel or too fast (we can mention ps/2
as an example of a 16 bytes limit).

> 
> Likewise the usb hid devices can buffer up to 16 events.  In that case
> it is just a qemu implementation detail and not a property of the
> hardware we are emulating, so it can be changed.  Not trivially though
> as the buffer is part of the migration data, so it is more work that
> just changing a #define.