Re: [Qemu-devel] [PULL for-2.1 0/2] vnc: fix two vnc update issues.

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> > So are these *really* release critical bugs, if they've been
> > only found in code review? We're really close to release now
> > and so my preference is not to include changes unless they're
> > really necessary...
> 
> These are fixing openQA breakage (os-autoinst),

In more detail:

Stephan's patch fixes a rather serve violation of the vnc protocol.  If
vnc clients ask for a complete framebuffer update they may not get it.
The complete display is tagged dirty, but nothing is sent out until
something changes on the screen, thereby triggering processing of all
dirty display regions.  Which may be never.

The other patch fixes a simliar situation.  Screen updates might become
stuck in case vnc delays processing due to output buffers being filled.
Again other screen updates will trigger dirty processing and un-stuck
the updates.

That kind of bug you usually don't notice as normal user.  You'll wiggle
the mouse and the mouse pointer update will make vnc flush things.  Or,
if in text mode, the friendly blinking cursor causes regular vnc screen
update activity.  Thats why it didn't trip up normal users.

Scrips are much more likely to hit it as they don't do random mouse
activity.  But even openQA doesn't hit it on every run, but only now and
then.

Also asking for a complete framebuffer update isn't something desktop
vnc clients usually do (after initial connect).  openQA does it though.

cheers,
  Gerd