On Thu, Sep 22, 2016 at 01:12:22PM +0200, Markus Armbruster wrote:
> "Daniel P. Berrange" <berra...@redhat.com> writes:
>
> > On Thu, Sep 22, 2016 at 10:36:45AM +0200, Markus Armbruster wrote:
> >> Don't make up a description in user_creatable_help_func(), improve the
> >> description infrastructure and its use so you get more useful ones
> >> there.
> >>
> >> The existing description infrastructure is just Property member
> >> description and object_property_set_description(). Rarely used, so
> >> description is generally null.
> >>
> >> Calling object_property_set_description() more often could be helpful,
> >> but to come up with a sensible description string, you need to know what
> >> the property does. Needs to be left to people actually familiar with
> >> the objects.
> >>
> >> Aside: historically, we add properties to *instances*. All the property
> >> meta-data gets duplicated for every instance, including property
> >> descriptions. This is more flexible than adding the meta-data to the
> >> class. The flexibility is rarely needed, but the price in wasted memory
> >> is always paid. Only since commit 16bf7f5, we can add it to classes.
> >> Adding lots of helpful property descriptions would increase the cost of
> >> instance properties further.
> >
> > FWIW, we could easily optimize handling of description strings by
> > applying the same trick that GLib has done for GObject property
> > descriptions.
> >
> > Almost certainly every call to object_property_set_description is
> > going to be passing a string literal, not a dynamically allocated
> > string. So we take advantage of that and in fact mandate that it
> > is a string literal, and thus avoid the strdup() of description.
> >
> > We can place a fun game to enforce this at compile time thus:
> >
> > - Rename object_property_set_description() to
> > object_property_set_description_internal()
> >
> > - Add the macro
> >
> > #define object_property_set_description(obj, name, desc, errp) \
> > object_property_set_description_internal(obj, name, "" desc "", errp)
>
> Cute :)
>
> > None the less, we really should make an effort to switch things
> > over to use class properties instead of instance properties, as
> > its going to save us allocating a 64 byte struct per property
> > per instance
>
> Yes, please.
>
> Related: a way to define a bunch of properties as *data*, i.e. an array
> of property descriptions, commonly static. Reasoning about static data
> is so much easier than reasoning about code.
IMHO we should go further and leverage QAPI schema to auto-generate all
the tedious boilerplate code for QOM objects
eg, consider the crypto/secret.c object file.
We could declare it as
{ 'object': 'QCryptoSecret',
'parent': 'Object',
'properties': {
'format': 'QCryptoSecretFormat',
'data': 'str',
'file': 'str',
'keyid': 'str',
'iv': 'str'
} }
Based on that it would have enough knowledge to generate
- struct QCryptoSecret definition + typedef
- struct QCryptoSecretClass definition + typedef
- TYPE_CRYPTO_SECRET macro
- QCRYPT_SECRET() cast macro
- Setters & getters aka
qcrypto_secret_prop_set_format
qcrypto_secret_prop_get_format
qcrypto_secret_prop_set_data
qcrypto_secret_prop_get_data
qcrypto_secret_prop_set_file
qcrypto_secret_prop_get_file
qcrypto_secret_prop_set_keyid
qcrypto_secret_prop_get_keyid
qcrypto_secret_prop_set_iv
qcrypto_secret_prop_get_iv
- qcrypto_secret_finalize
- qcrypto_secret_class_init
- TypeInfo qcrypto_secret_info variable
- qcrypto_secret_register_types() method
- type_init(qcrypto_secret_register_types);
That'd massively reduce the work to create new objects, to just
filling in the semantically useful logic
Regards,
Daniel
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