LibRaw::raw2image() allocates imgdata.image[] array and copies data from internal storage (different for Bayer and non-bayer images) to this array.
No demosaic, no black subtration, this is for developers who want to do processing by hand.

So, three ways exists:
- unpack() + raw2image() - this produce internal data compatible with old LibRaw (0.9-0.13)
- unpack + dcraw_process() - for full processing
- only unpack() but you need to know LibRaw internals, because different data types (bayer vs non-bayer) are stored in different way.

Sure, internals may change in future LibRaw releases, so it is safer to use unpack() + raw2image, although it requires extra RAM.