Re: [Qemu-devel] [PATCH 3/6] luks: Support .bdrv_co_create

[Eric Blake <eblake@redhat.com>]

On 03/12/2018 06:47 AM, Kevin Wolf wrote:

>>> +##
>>> +{ 'struct': 'BlockdevCreateOptionsLUKS',
>>> +  'data': { 'file':             'BlockdevRef',
>>> +            'qcrypto':          'QCryptoBlockCreateOptionsLUKS',
>>> +            'size':             'size' } }
>>
>> s/qcrypto/crypto/ in this field.
>>
>> I do wonder about whether instead of embedding QCryptoBlockCreateOptionsLUKS
>> as a field, we could instead use QCryptoBlockCreateOptionsLUKS as the
>> base struct and just inherit from it to add file/size.
>>
>> I'm not really fussed, but I wonder if you/Eric have any thoughts on the pros
>> or cons of inheritance vs embedding in this case.
> 
> I don't think QAPI has a way to embed it in JSON, but still provide a
> QCryptoBlockCreateOptionsLUKS C object. Originally I wanted to use
> inheritance, but instead of having the struct type reused, you get all
> field definitions copied. I guess you could then manually cast to the
> base type and it would still work, but it didn't really feel clean.

The QAPI generators generate a function (qapi_NAME_base()) which will 
convert any derived type back to the parent class, which is cleaner than 
manually casting; if that makes the decision to use inheritance any easier.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org