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

["Daniel P. Berrange" <berrange@redhat.com>]

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.

> --
> 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

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.

Regards,
Daniel
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