Add module element in updateinfo.xml

[kontura]

Two features:

• add CMake support for python interpreter path, so its possible to either specify python version or path to interpreter
• add support for module element in updateinfo.xml

[dmach]

@kontura could you split the python changes into a new PR?
I'd probably merge it in soon, but the modularity part will probably stay open for a while...

[Conan-Kudo]

I'm a little concerned we're just randomly extending the updateinfo.xml format here, especially since createrepo_c cannot validate or create module XML metadata.

If we want to merge this, I really want this guarded by a flag, because it technically generates invalid updateinfo.xml per the schema for it.

[dmach]

@Conan-Kudo could you be more specific about the module XML metadata?
What do you mean exactly?
The goal here is to extend updateinfo with module identifiers (N:S:V:C:A)
so we can track relation between streams and RPMs.

About the updateinfo.xml schema - do you know who owns it and where it lives?
We definitely want to stay in sync with the schema.
The updateinfo.xml from F29 doesn't contain any schema link and that makes me think that the format is more a tribal knowledge than a proper standard.

[Conan-Kudo]

@dmach I mean that createrepo_c can't validate links between the XML data in updateinfo about modules and the modules YAML data to make sure it is valid.

As for the updateinfo.xml schema... I know of two schema definitions that exist. One is in python-Updateinfo, which comes from Scientific Linux. This project attempts to rationalize the variation between Bodhi and OBS's implementations. The other is in libzypp, which I think was used to do the original implementation of the YUM/RPM-MD format for Zypper a decade ago...

[dmach]

@Conan-Kudo I think validating links between updateinfo.xml and modulemd is out of scope.
This has to be tested outside createrepo_c.
If you think about it, updateinfo RPMs are not validated against primary.xml either.

Thanks for the schema links.

[Conan-Kudo]

@dmach Hmm.

[goosemania]

@kontura, is there a reason for a version to be of gchar type?
In libmodulemd it's guint64.

[kontura]

I have updated it to be guint64 as well.
One thing I am not sure about, what should happen when the parsing of the version number fails? Is setting it to 0 ok?