Re: [Qemu-devel] [PATCH 12/13] qapi: support for keyworded variable-length argument list

[Anthony Liguori]

On 03/29/2012 01:42 PM, Luiz Capitulino wrote:
> On Thu, 29 Mar 2012 13:26:34 -0500
> Anthony Liguori<address@hidden>  wrote:
>
> > On 03/29/2012 12:26 PM, Luiz Capitulino wrote:
> > > This allows for QAPI functions to receive a variable-length argument
> > > list. This is going to be used by device_add and netdev_add commands.
> > >
> > > In the schema, the argument list is represented by type name '**',
> > > like this example:
> > >
> > >       { 'command': 'foo', 'data': { 'arg-list': '**' } }
> > >
> > > Each argument is represented by the KeyValues type and the C
> > > implementation should expect a KeyValuesList, like:
> > >
> > >       void qmp_foo(KeyValuesList *values_list, Error **errp);
> > >
> > > XXX: This implementation is simple but very hacky. We just iterate
> > >        through all arguments and build the KeyValuesList list to be
> > >        passed to the QAPI function.
> > >
> > >        Maybe we could have a kwargs type, that does exactly this but
> > >        through a visitor instead?
> > >
> > > Signed-off-by: Luiz Capitulino<address@hidden>
> >
> > What about just treating '**' as "marshal remaining arguments to a string" and
> > then pass that string to device_add?  qmp_device_add can then parse that string
> > with QemuOpts.
>
> If this turns out to be simple enough, I'm fine with it.

I don't love doing this sort of double conversion but it's really the only 
practical way to do it I think.  device_add has a weird semantic where 
printing/parsing is implied so I think it's unavoidable.

> > It's a bit ugly, but that's how things worked.  When we introduce qom_add, this
> > problem goes away because you would make multiple calls to qom_set to set all of
> > the properties.
>
> Just out of curiosity, is qom_add going to supersede device_add?

Eventually...

I'd like to see qom_add as the low level interface but then I'd like to see nice 
high level interfaces like 'block_add' which took a parameter of virtio-blk and 
did all of the magic to create a block device in such a way that's compliant to 
the current machine type.

Regards,

Anthony Liguori