Re: [Qemu-devel] [RfC PATCH 0/5] console: qom-ify & extent screendump monitor command

[Eric Blake <eblake@redhat.com>]

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On 04/19/2013 02:37 AM, Markus Armbruster wrote:
>> Question for the libvirt guys:  Is it ok for libvirt to just extend the
>> existing screendump command?  Can libvirt figure there is a new
>> (optional) parameter?  See patch #5.
> 
> Nope, QMP can't do that.  I argued for such capabilities, but the
> "create a new command" philosophy prevailed.
> 
> Go forth and multiply commands!  And have fun picking command names that
> aren't fugly.

Adding optional parameters to an existing command has been done before;
drive-mirror gained 'granularity' and 'buf-size' in 1.4 even though the
command existed in 1.3.

What would make it possible to avoid an explosion of new commands is a
way to introspect WHICH options are available for a given command.  We
don't have that yet, but if we add a command that returns the JSON
representation of what the command expects, THAT would make it
acceptable to add optional arguments to an existing command in a way
that libvirt could query to see whether the qemu it is talking to
supports the optional arguments.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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