Re: [Qemu-devel] [PATCH] vl: add -libvirt-caps option for libvirt to stop parsing help output

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

On Fri, Jul 27, 2012 at 01:23:03PM +0200, Markus Armbruster wrote:
> "Daniel P. Berrange" <berrange@redhat.com> writes:
> > The above would take care of probably 50% of the current libvirt
> > capabilities probing, including a portion of the -help stuff. Then
> > there is all the rest of the crap we detect from the -help. We could
> > just take the view, that "as of 1.2", we assume everything we previously
> > detected is just available by default, and thus don't need to probe
> > it.  For stuff that is QOM based, I expect we'll be able to detect new
> > features in the future using the qom-XXX monitor commands. For stuff
> > that is non-qdev, and non-qom, libvirt can just do a plain version
> > number check, unless we decide there is specific info worth exposing
> > via other new 'query-XXX' monitor commands.
> 
> Assuming version X (according to query-version) supports no less than
> upstream version X sounds fair.
> 
> If a command line option has a corresponding QMP command, probing QMP
> for the feature suffices.  For instance, query-devices gives you devices
> for -device.
> 
> I'm afraid there could still be an occasional need for probing the
> command line.  A simple, machine-readable command line self-description
> could satisfy it.  Something like:
> 
> - query-cmdline-options: JSON representation of qemu_options[], with
>   unnecessary detail elided.  Basically option name and whether it takes
>   an argument.
> 
> For options with a QemuOpts argument, we may want to add argument
> self-description.  Basically its QemuOptsList, with unnecessary detail
> elided.  Non-QemuOpts arguments don't get that.  New structured option
> arguments should use QemuOpts anyway.

I think you are quite possibly correct, but for the sake of enabling
us to move forward without more arguments, my inclination is to ignore
this just now :-) Lets get the new commands Anthony posted merged, and
port libvirt to use this new approach. Once that's all done, we can
evaluate whether there is a any more information we ought to provide
which might require a query-cmdline-options, or something else more
targetted (eg query-chardev-options or something)


Daniel
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