Re: [Qemu-devel] [PATCH v2] Show values and description when using "qom-list"

[Markus Armbruster <armbru@redhat.com>]

Markus Armbruster <armbru@redhat.com> writes:

> Andreas Färber <afaerber@suse.de> writes:
>
>> Am 08.06.2018 um 11:41 schrieb Dr. David Alan Gilbert:
>>> * Andreas Färber (afaerber@suse.de) wrote:
>>>> Am 01.06.2018 um 17:39 schrieb Ricardo Perez Blanco:
>>>>> For debugging purposes it is very useful to:
>>>>>  - See the description of the field. This information is already filled
>>>>>    in but not shown in "qom-list" command.
>>>>
>>>> No objection on this part.
>>>>
>>>>>  - Display value of the field.
>>>>
>>>> That is by definition the qom-get operation, not qom-list. Just like the
>>>> ls command does not show file contents, there's cat etc. for that. For
>>>> debugging purposes we had a qom-tree (?) command that would combine
>>>> both.
>>>
>>> I'm not too bothered about distinguishing between the two commands;
>>> but it would be nice
>
> When an HMP and QMP both have a command with the same name, they should
> do the same.
>
> HMP may add convenience features that aren't wanted in QMP, but I feel
> extending an operation to list objects to also show their contents goes
> beyond that.  If we want an HMP command that does both, it should be
> named differently.  Perhaps that might even be more appropriate for HMP
> than low-level commands qom-list and qom-get, but I leave that to the
> HMP maintainer to decide.
>
>>>                      - one reason I'm not too bothered is because we've
>>> failed to get a qom-get in multiple years of trying.
>
> We clearly haven't tried hard enough.
>
> If we can figure out how to show values in qom-list, surely we can
> figure out how to show them in qom-get.
>
>>>>       There might be unmerged patches on qemu-devel related to display
>>>> of certain data types.
>>> 
>>> Which ones?
>>
>> My original qom-info series needed StringOutputVisitor changes for enums
>> (test case: rtc) that did not get accepted immediately and thus some
>> part of HMP qom-info/qom-get got stuck due to risking assertions for
>> qom-info / otherwise; QMP was not affected IIRC.
>
> Here's the last try I can find:
> [PATCH v2] qom: Implement qom-get HMP command
> Message-Id: <1473157086-12062-1-git-send-email-dgilbert@redhat.com>
> https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg01041.html

Stalled on output format and consistency with qom-set.  I wrote back
then "We can take qom-get as is and improve its output later."  I'd like
to encourage you to dust it off.  Perfect's the enemy of good.

Wanted improvements include:

* Prettier output format.  I'd suggest creating a keyval variant of the
  output visitor.

* Make qom-set input format consistent by switching to the matching
  input visitor.

> Its v1 tries a different approach:
> [PATCH 0/2] qom-get [for 2.8]
> Message-Id: <1472117833-10236-1-git-send-email-dgilbert@redhat.com>
> Unfortunately the mailing list archive doesn't show the full thread, so
> you get to follow three links:
> https://lists.gnu.org/archive/html/qemu-devel/2016-08/msg03815.html
> https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg04261.html
> https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg04267.html

This one stalled on string visitor limitations.  You didn't feel like
addressing them just to get qom-get working.  Understandable.