Re: [Qemu-devel] [PATCH 0/2] Tunnel character device data over VNC (v1)

[Gerd Hoffmann <kraxel@redhat.com>]

On 07/01/09 21:59, Anthony Liguori wrote:
> Gerd Hoffmann wrote:
>> Monitor is a special case. Multiple connections to the same session
>> are not very useful there. Multiple sessions are a different (albeit
>> related) problem.
>
> Serial is the same. Imagine a bash shell running on the serial port with
> two VNC client connected and stdio connected. Utter chaos. You really
> want to use one or the other, never both at the same time.

Typing to both at the same time isn't going to work well indeed.  IMHO 
that isn't a reason to enforce one connection only though.  It is still 
a useful feature.  Use case:

vm running at your workstation in the office, with -serial tcp.  You are 
heading home, leaving telnet connected.  At home you'll find you want to 
check something in your vm via vpn.

With current qemu:  You have to zap the telnet session somehow to be 
able to connect.

With switching:  You have to talk to the monitor to reconfigure things.

With multiple connections and multiplexing:  You'll just connect, type a 
few commands, disconnect, done.  You'll even see what you have done when 
you come back to the office the next day.

Also note that the vnc server accepts input from multiple clients as 
well, which can lead to simliar problems.  Nobody wants to kill support 
for multiple clients just because of that, because in practice it isn't 
a issue.


Monitor is different for two reasons:

First, we could actually open a new session.  That wouldn't work for 
serial as we can't hotplug a serial line into the guest on connect.

Second, if the monitor is used by libvirt or some other management app a 
second connection to the same session is seriously harmful.

cheers,
   Gerd