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Re: [libvirt] [Qemu-devel] fix/re-do query-command-line-options



Il 28/01/2014 14:16, Markus Armbruster ha scritto:
That would mean we can't ever add an option that doesn't take an
argument again.

We can add it under an existing QemuOpts group or invent a new one
(like we did for -rt or -msg).

Do you mean -rtc?

I meant -rt, but -rtc applies just as well. :)

-msg takes a timestamp=on/off argument.  I guess that doesn't feel too
forced, because we could conceivably have more settings related to error
reporting.

Do you mean to suggest new options should always be done in a way that
makes them fit into QemuOpts?

Yes.  Not into *existing* QemuOpts of course.

How would you add something like -S, -nodefaults, or -daemonize?

I would add -nodefaults and -S to -machine. I would deprecate -daemonize. But that's just for the sake of -readconfig. Consumers of introspection can just "know" that those options are there.

The question is whether we should extend QemuOpts to cover options
without arguments, or change the options without arguments to fit into
existing QemuOpts, e.g. by making them all syntactic sugar for a
suitable QemuOpts-style option.

If we do the latter, we need to tell customers of command line
introspection to look only for the desugared forms.

Yeah.

(b) document the QemuOpts schema for -acpitable, -smbios, -netdev,
-net. These options validate the options with OptsVisitor, so we could
do without QemuOpts schema, but we know the schema won't bitrot
because we never remove suboptions.

-device?

-device already provides its own introspection via "qom-list-types"
and "-device driver,?".

We're discussing introspection via QMP, so "-device driver,help" doesn't
count.

qom-list-types with argument "implements": "device" together with
device-list-properties indeed lets you introspect device models and
their properties.  You then need to to know how to translate that to
the command line.  For instance, you need to know that "type": "on/off"
in the former means "type": "boolean" in the latter, and so forth.

Yes.  That's what I actually meant.  O:-)

What I'd like to see is more unified introspection, not this smattering
of one-offs hacked up without too much thought to serve some immediate
need we have now.

We already have something that aspires to be our unified interface
description: QAPI schemata.  Perhaps we should make it our unified
introspection mechanism while we're at it.

QOM introspection can use QAPI schemata.  Property types should be one of:

* child<ClassName>

* link<ClassName>

* QAPI scalar type

* QAPI compound type

I see QOM introspection as orthogonal to QAPI introspection, and QemuOpts introspection as complementary to both:

       command line introspection        QMP introspection
         |                    |            |        |
         |                    v            |        |
         v           QOM introspection  <--'        |
      QemuOpts                |                     |
    introspection             v                     |
                    QAPI introspection  <-----------'

Makes any sense? :)

(b) documenting the schemata is not harder than what Amos proposed.

(c) schema inspection for objects remains a problem, but one that we
need to solve anyway so it doesn't affect query-command-line-options.

As long as we don't have such schema inspection, I'm rather reluctant to
reject alternative means to solve problems people have *now*.

Note the "doesn't affect query-command-line-options" part.  Amos's
patch do not solve the problem of which classes can be instantiated
with -object, or of which properties can be used.

Possible misunderstanding on my part.  I was afraid you were arguing to
solve -object introspection *instead* of Amos's incremental improvement,
but that doesn't seem to be the case.

Well, I was arguing against this series. I think it provides little benefit and has a comparatively high cost in terms of future backwards compatibility.

I was arguing for ignoring non-QemuOpts options and focus on what really matters, which is QemuOpts, QOM and QAPI introspection. The first is already there and can be fixed by adding schemata for -acpitable and friends. QAPI introspection is already being tackled by Amos.

QOM/-object is indeed the elephant in the room, but luckily we have enough few users that I believe we can do it if we agree on the right design.

Paolo


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