Re: [Qemu-devel] [PATCH 14/17] monitor: Decouple terminals

[Anthony Liguori]

Jan Kiszka wrote:
> Currently all registered (and activate) monitor terminals work in
> broadcast mode: Everyone sees what someone else types on some other
> terminal and what the monitor reports back. This model is broken when
> you have a management monitor terminal that is automatically operated
> and some other terminal used for independent guest inspection. Such an
> additional terminal can be a multiplexed device channel or a gdb
> frontend connected to QEMU's stub.
>
> Therefor, this patch decouples the buffers and states of all monitor
> terminals, allowing the user to operate them independently. The basic
> idea is stolen from Jason Wessel: When starting to handle a monitor
> command or some terminal event, the current monitor terminal is set to
> the one associated with the underlying char device, letting all
> succeeding monitor_printf show up on only this selected terminal.
>
> There are still two asynchronous monitor writers: some error reporting
> in VNC's audio_add and the log-to-monitor feature of the audio
> subsystem.

That concerns me.  Nothing should output to the monitor asychronously.

I'd like to see a few changes to make things a bit closer to the long 
term goals for the monitor (having proper multiple monitors devoid of 
global state).

Here's what I'd suggest:

1) Make monitor_printf() take a monitor state.  The easiest thing to do 
would be to introduce this in your previous rename patch making 
everything use current_monitor.
2) Introduce current_monitor and default_monitor global variables.  They 
map to what you describe above and should be maintained as such.
3) Make all monitor callbacks take a monitor state
4) Convert monitor_printf()s called from monitor callbacks to use the 
passed monitor state
5) Eliminate all uses of current_monitor/default_monitor.

I'd say, 1 and 2 are required for this patchset.  I think 3 and 4 would 
be pretty easy to add to your patchset.  I think 5 is probably tougher 
and could wait for another day.

Regards,

Anthony Liguori