[Xen-devel] Re: [PATCH] qemu vnc updates

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

Stefano Stabellini wrote:
> Hi all,
> reading qemu code I realized that the qemu vnc server sometimes sends 
> framebuffer updates even if the client didn't request any.
> This is not consistent with the RFB protocol spec and can break some 
> clients.

It's actually consistent with the RFB spec.  Have you seen any clients 
break?
The RFB spec states pretty clearly that a single 
FramebufferUpdateRequest may generate 0 or more FramebufferUpdate 
events.  Once a client has sent a single FramebufferUpdate request, it 
should expect to continue to receive more FramebufferUpdates for an 
indefinite period of time according to the specification.
Regards,

Anthony Liguori

> The patch I am attaching strictly enforces compliance with the RFB 
> protocol making sure framebuffer updates are sent only if the client 
> requested one.
> Doing so is more difficult than it seems because some framebuffer 
> pseudo-encoding updates cannot be discarded but must be sent anyway: for 
> example desktop resize and pixel format change messages. To solve the 
> problem I wrote a queue that stores those messages and sends them as 
> soon as the client asks for an update.
> Since 90% of the times the queue is used to store only few elements, the 
> queue allocates 10 elements at the beginning and every time it runs out 
> of elements allocates other 10 elements. This is should drastically 
> limit the number of malloc and free needed to maintain the queue.
> I did some stress tests in the last couple of days and seems to work well.
> Best Regards,
>
> Stefano Stabellini
>
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
>
>
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