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

[Anthony Liguori <aliguori@us.ibm.com>]

On 03/29/2012 01:42 PM, Luiz Capitulino wrote:
> On Thu, 29 Mar 2012 13:26:34 -0500
> Anthony Liguori<aliguori@us.ibm.com>  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<lcapitulino@redhat.com>
>>
>> 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