On Wed, Jan 20, 2021 at 10:25:25AM +0200, Dov Murik wrote:
> Hi John,
>
> On 19/01/2021 22:02, John Snow wrote:
> > On 1/17/21 2:27 AM, Dov Murik wrote:
> > > Detect whether qmp-shell's standard input is not a TTY; in such case,
> > > assume a non-interactive mode, which suppresses the welcome banner and
> > > the "(QEMU)" prompt. This allows for easier consumption of qmp-shell's
> > > output in scripts.
> > >
> > > Example usage before this change:
> > >
> > > $ printf "query-status\nquery-kvm\n" | sudo
> > > scripts/qmp/qmp-shell qmp-unix-sock
> > > Welcome to the QMP low-level shell!
> > > Connected to QEMU 5.1.50
> > >
> > > (QEMU) {"return": {"status": "running", "singlestep": false,
> > > "running": true}}
> > > (QEMU) {"return": {"enabled": true, "present": true}}
> > > (QEMU)
> > >
> > > Example usage after this change:
> > >
> > > $ printf "query-status\nquery-kvm\n" | sudo
> > > scripts/qmp/qmp-shell qmp-unix-sock
> > > {"return": {"status": "running", "singlestep": false,
> > > "running": true}}
> > > {"return": {"enabled": true, "present": true}}
> > >
> > > Signed-off-by: Dov Murik <dovmu...@linux.vnet.ibm.com>
> >
> > Hiya! I've been taking lead on modernizing a lot of our python
> > infrastructure, including our QMP library and qmp-shell.
> >
> > (Sorry, not in MAINTAINERS yet; but I am in the process of moving these
> > scripts and tools over to ./python/qemu/qmp.)
>
> Thanks for this effort.
>
> >
> > This change makes me nervous, because qmp-shell is not traditionally a
> > component we've thought of as needing to preserve backwards-compatible
> > behavior. Using it as a script meant to be consumed in a headless
> > fashion runs a bit counter to that assumption.
> >
> > I'd be less nervous if the syntax of qmp-shell was something that was
> > well thought-out and rigorously tested, but it's a hodge-podge of
> > whatever people needed at the moment. I am *very* reluctant to cement
> > it.
>
> Yes, I understand your choice.
>
>
> >
> > Are you trying to leverage the qmp.py library from bash?
>
> Yes, I want to send a few QMP commands and record their output. If I use
> socat to the unix-socket I need to serialize the JSON request myself, so
> using qmp-shell saves me that; also not sure if there's any negotiation done
> at the beginning by qmp-shell.
There is a handshake, but it is just a single json message.
See docs/interop/qmp-intro.txt and qmp-spec.txt for guidance.
> Is there an easier way to script qmp commands, short of writing my own
> python program which uses the qmp.py library?
Yes, writing your own python program is probably best. Doing anything
complex is shell is almost always a mistake, as it is a very crude
and poor language compared to something like managing QEMU/QMP.
Note that I don't believe that we've declared qmp.py to be a long
term stable interface for users outside of QEMU either. An alternative
is to just use the python sockets APIs directly to speak to QEMU/QMP
Regards,
Daniel
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