Investigate "XVC-MDU" block

[emoose]

Newly added kind of block located just before hash table begins, seems to store 1 byte for each XVC region in the image, some places in xvdd.sys call this area the "presence map", is apparently used to create the "XCT", unsure what any of that means though..

My guess is the byte indicates the presence of the region, I've only seen the value of 3 used so far, so I guess 3 must mean the region is present? Other values might mean the region is missing/being downloaded/???

Not sure if this area is hashed/signed at all, after the NumMDUBlocks field in the header is a 0x10 array of bytes that seem filled with data (was formerly unused), could be a hash, but haven't been able to find how to make a hash that matches (also haven't seen any code in xvdd.sys that actually checks that 0x10 array...)

[emoose]

Extracted definitions from xvdutil, now xvdtool can read this block but haven't implemented writing yet, so leaving this issue open for now.

[tuxuser]

Solved by #20

[emoose]

Well #20 adds new mutable data, but atm there's no way for us to edit existing data and then write out the edited data... should probably leave this open till we have that (something like that would also be required for save_new_xvd I guess)