Problem GOS read_links of "follow-on" BKPF document

Question

Hello,
I have problem reading GOS links ( with CL_BINARY_RELATION=>read_links or any similar methods/FMs ) of FI document (type BKPF).
In SRGBTBREL table there are also no entries for this BKPF document  (in INSTID_A).
BUT I can see attachments + notes in FB03 Attachment list for this document.
After debbuging FB03 Attachment list I have found, that BKPF document does not have directly attached files, even though I can see them in FB03. Because it is "follow-on document" for invoice (which have some attached files), and there is also WF and PO in relationship browser (they have also another attachments, seen in FB03).
FB03 GOS attachment list prepares all these objects (document,invoice,WF,PO..) and reads attachments for all of them.
My question - how to read these links / attachments when I know only BKPF document in my program? Do I have to somehow programaticaly search for previous objects (invoice, PO, WF..) and after it read their attachments? I Thought that it is done automaticaly by CL_BINARY_RELATION=>read_links)...
Problem is on 731 release.

Answer 1

Ok, I answer to myself with what I found so far:
In FB03 attachments are obtained from bussines objects:    
BKPF (document itself) - can be read by read_links, but in my case I have none attachmens on BKPF directly
BUS2081 (invoice) - can be read by read_links, but need use BKPF-AWKEY = RBKP-BELNR & GJAHR as key
I also found unreleased function FB_DOC_GET_GOS_LINKS which helped me a lot to understand where attachments come from.
In my case it was all from BUS2081 invoice. Few attachments directly attached in GOS (read by read_links method) and rest were attached on content server (can be read for example with ALINK_RFC_DOCUMENTS_GET).