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

["Chun Yan Liu" <cyliu@xxxxxxxx>]

>>> On 9/10/2014 at 11:47 AM, in message
<CA+aC4ktktHx8VtvKSvSoH-YZtF_EE0-U2DO=y55wRUZjzSf8gA@xxxxxxxxxxxxxx>, Anthony
Liguori <anthony@xxxxxxxxxxxxx> wrote: 
> 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.

About this question, my colleague sent mail to TigerVNC upstream before,
but they are not convinced  that TigerVNC behaves wrong. VNC protocol
doesn't specify which way is right for pressing key for long time.
(key-down, key-up, key-down, key-up...
or key-down, key-down, key-down, ...., key-down, key-up)
To them, they don't think 'key-down, key-down, ..., key-down, key-up' is
wrong. RealVNC for Windows also send the same events as TigerVNC.

Yeah, it's really a disputable thing. SPICE is much better in this case.
 
>  
> Regards, 
>  
> Anthony Liguori 
>  
> >> 
> >> [...] 
> >> 
> >> 
> > 
> > 
> > 
>  
>  


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