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Re: [Qemu-arm] [Qemu-devel] [RFC v3] qapi: command category to stimulate
From: |
Daniel P . Berrangé |
Subject: |
Re: [Qemu-arm] [Qemu-devel] [RFC v3] qapi: command category to stimulate high-level machine devices |
Date: |
Thu, 7 Jun 2018 11:33:07 +0100 |
User-agent: |
Mutt/1.9.5 (2018-04-13) |
On Thu, Jun 07, 2018 at 11:24:55AM +0100, Stefan Hajnoczi wrote:
> On Mon, Jun 04, 2018 at 12:12:21PM +0200, Gerd Hoffmann wrote:
> > On Mon, Jun 04, 2018 at 10:29:40AM +0100, Peter Maydell wrote:
> > > On 4 June 2018 at 10:20, Stefan Hajnoczi <address@hidden> wrote:
> > > > Many of these inputs/outputs can be tied to an external UI. A degree of
> > > > timing precision is required so that the UI is responsive, although
> > > > cycle-accurate timing is not what I'd expect from QMP.
> > >
> > > Would we also be able to tie them to an internal UI, ie
> > > something that appears as another view in the GTK/etc
> > > UI frontends we have?
> >
> > Should be doable too. Basically a display device, which isn't a *real*
> > display but the UI. Could show a rendering of the board, simliar to how
> > web emulation environments are doing it. LED status could be rendered
> > directly to the board. A virtual mouse could map mouse clicks to button
> > presses.
> >
> > Doing more complex input that way (say a slider for the temperature
> > sensor) isn't going to work very well though ...
> >
> > Sensor input in general is pretty much unsupported in qemu.
>
> For the micro:bit we've been thinking of a WebSocket monitor interface.
> This way a web UI can work with both local and remote QEMU instances.
>
> For security reasons, the WebSocket cannot be the regular QMP monitor.
FWIW, add ability to use websockets protocol over chardevs is fairly
easy. We already have a QIOChannelWebsock for the VNC server, so it
is just a little work to wire it into the chardev.
If the -monitor / -qmp arg took a filename containing a whitelist of
allowed monitor commands, you could indeed use the regular QMP monitor
instead of writing something new.
> A slimmed down monitor is required with a subset of QMP commands and
> events. For example, users must not be able to migrate to an exec:
> destination so we need to ban that command on the UI monitor :-).
FWIW, you could use the "-sandbox spawn=off,elevateprivileges=off"
arg to prevent ability of QEMU to fork/exec/setuid. Even if the
monitor still allows it, it thus get blocked, albeit by immediately
terminating the process.
> Pros:
> + Remote control is possible over sockets
> (Important for hosting QEMU on a server. Nowadays this is becoming a
> popular way to deliver emulation to users. They don't need to
> install software locally.)
> + UI is cleanly isolated from QEMU process
> Cons:
> - Binary or high-frequency I/O is a bad fit for a JSON WebSocket
> interface
>
> I prefer the WebSocket route over creating a fake display that will not
> be able to implement complex widgets well.
Regards,
Daniel
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Re: [Qemu-arm] [RFC v3] qapi: command category to stimulate high-level machine devices, Gerd Hoffmann, 2018/06/04