Raw device I/O for large objects

Hello,

I am a graduate student of computer science and I have been looking at 
PostgreSQL for my master's thesis work.

I am looking into implementing raw device I/O for large objects into 
PostgreSQL (maybe for all storage, I'm not sure which would be 
easier/better). I am extremely new to the codebase, however.

Could someone please point me to the right places to look at, and how/where to 
get started? Would such a development be useful at all? Is anyone working on 
anything related?

Any feedback / information would be highly appreciated!

Thanks,
Georgi