On Fri, Feb 20, 2015 at 03:49:05PM -0700, Eric Blake wrote:
Hello and thanks for your comments.
> 1. implement QAPI introspection (we've been dreaming about this
> since qemu 1.5 days), then the caller just queries to see if the
> version of QMP has the optional 'top' parameter.
This sounds like the best option. Is there a roadmap? What's the
status?
I guess the amount of work depends a lot on the goals, but from what
I can see, something like a 'query-command-args' command that returns
the list of parameters is trivial, there's already the qmp_cmds array
in memory with all the necessary information.
> 2. implement the new feature as a new command (then the existing
> 'query-commands' becomes an easy probe; but we have code duplication
> with existing commands)
I don't think there would be a lot of code duplication because one
operation is a strict superset of the other, we would be just adding
unnecessary commands. I would go for option 1) if possible.
> 3. guarantee that we have sane error messages for bogus
> commands used as the probe. If {"execute":"block-stream",
> "data":{"device":"no-such","top":"bogus"}} gives a reliable
> DeviceNotFound error for qemu that supports optional 'top', and a
> reliable GenericError about an unknown argument 'top' in older qemu
It doesn't seem like the best solution considering the alternatives,
but for what it's worth:
Current QEMU:
(QEMU) block-stream device=no-such top=bogus
{u'error': {u'class': u'GenericError', u'desc': u"Invalid parameter 'top'"}}
With my patch:
(QEMU) block-stream device=no-such top=bogus
{u'error': {u'class': u'DeviceNotFound', u'desc': u"Device 'no-such' not
found"}}
Regards,
Berto
