Re: [Qemu-devel] [PATCH v2] qom: Implement qom-get HMP command

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Daniel P. Berrange (berrange@redhat.com) wrote:
> On Tue, Sep 06, 2016 at 11:18:06AM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > This started off as Andreas Färber's implementation from
> > March 2015, but after feedback from Paolo morphed into
> > using the json output which handles structs reasonably.
> > 
> > Use with qom-list to find the members of an object.
> > 
> > (qemu) qom-get /backend/console[0]/device/vga.rom[0] size
> > 65536
> > (qemu) qom-get /machine smm
> > "auto"
> > (qemu) qom-get /machine rtc-time
> > {
> >     "tm_year": 116,
> >     "tm_sec": 0,
> >     "tm_hour": 9,
> >     "tm_min": 46,
> >     "tm_mon": 8,
> >     "tm_mday": 6
> > }
> 
> I'm not really a fan of us exposing JSON in the HMP, as it rather
> seems to defeat the purpose of using the HMP.

Well as long as it's clear and easily readable by humans I'm OK about it;
and I'm less fussed about it on the output side; JSON is much more painful
to use as human typed input.

> > --
> > v2
> >   switched from using string-output-visitor to qobject_to_json_pretty,
> >   drop string-output-visitor patch.
> 
> IIUC, you switched because string-output-visitor could not handle
> complex types.
> 
> I have previously written a text-output-visitor that could do
> this correctly, since we have this exact same requirement for
> 'qemu-info info' to print out the extra-block specific data
> in human friendly format for the LUKS driver.
> 
>   https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg01727.html

How close to going in is it? It looks from the comments that Eric
is thinking about fixing string-output-visitor.
I'm not clear why you'd want a text-output-visitor and a string-output-vistior.

> With your example that ought to lead to output looking like
> 
>  (qemu) qom-get /machine rtc-time
>     tm_year: 116
>     tm_sec: 0
>     tm_hour: 9
>     tm_min: 46
>     tm_mon: 8
>     tm_mday: 6
> 
> which i think is more suitable for the HMP.

Yes, it's a little prettier; I'm not fussed either way - but I just want to
make sure that we do end up with a qom-get; it's something I'd have found
useful in the past and I know others would have, and the code for it was
originally written by Andreas ~2.5 years ago - so if text-output-visitor is
imminent then sure, but if it's not then I suggest we stick with this.

Dave

> 
> Regards,
> Daniel
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--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK