Re: [Xen-devel] [Qemu-devel] [PATCH] vnc: add additional key up event before repeated key down

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

On Tue, Sep 9, 2014 at 8:31 PM, Chun Yan Liu <cyliu@xxxxxxxx> wrote:
>
>
>>>> On 9/10/2014 at 02:23 AM, in message 
>>>> <87tx4girg6.fsf@xxxxxxxxxxxxxxxxxxxxx>,
> Markus Armbruster <armbru@xxxxxxxxxx> wrote:
>> "Chun Yan Liu" <cyliu@xxxxxxxx> writes:
>>
>>>>>> On 9/6/2014 at 05:23 AM, in message
>> > <alpine.DEB.2.02.1409052202451.2334@xxxxxxxxxxxxxxxxxxxxxxx>, Stefano
>> > Stabellini <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> >> On Fri, 5 Sep 2014, Chunyan Liu wrote:
>> >> > Using xen tools 'xl vncviewer' with tigervnc (default on SLE-12),
>> >> > found that: the display of the guest is unexpected while keep
>> >> > pressing a key. We expect the same character multiple times, but
>> >> > it prints only one time. This happens on a PV guest in text mode.
>> >> >
>> >> > After debugging, found that tigervnc sends repeated key down events
>> >> > in this case, to differentiate from user pressing the same key many
>> >> > times. Vnc server only prints the character when it finally receives
>> >> > key up event.
>> >>
>> >> Is this actually how a vnc client should behave?
>> >> How do the vnc client and server from realvnc behave in this regard
>> >> (they are the reference implementation)?
>> >
>> > VNC protocol doesn't specify how to handle key repetition. Tightvnc
>> > sends key-down&key-up repeatedly, but some example like RealVNC for
>> > Windows does the same thing - it sends only repeated key-down.
>> >
>> > Generally the VNC keyboard handling gives lot of space for interpretation
>> > and so the implementations differ.
>>
>> If implementations differ, and QEMU already behaves like some of them,
>> then why change it?
>
> To change qemu side because we could not expect each VNC client behaves
> the same when holding key down, some sending key-down, key-up, key-down,
> key-up; but some sending key-down, key-down, key-down .... Without change,
> client only sending key-down, key-up, key-down,key-up ... can get correct
> display.

The VNC keyboard handling is pretty straight forward.   The keys sent
are symbolic and correspond to input events (as interpreted by an
application).  Whether you get repeat events depends on a lot of
client side configuration.

>>  What exactly gets fixed and what gets broken by the
>> proposed change?
>
> Holding the key down, only one character is printed, but repeated characters
> are expected. Happens on some vnc client. Either vnc client or vnc server
> should change some to match.

You should fix TigerVNC.  It's broken if it isn't sending repeat events.

Regards,

Anthony Liguori

>>
>> [...]
>>
>>
>
>
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