I'm using the NTFS MasterFileTable / USN journal of a few disk/partitions (C:, D:, E:, F:, etc), and I'd like to use a unique ID for each file/directory.
While I'm reading the USN_RECORD (also called PUSN_RECORD), there is this int64:
DWORDLONG FileReferenceNumber;
that is a unique file/directory identifier, unique at least in the current partition.
But there could be collisions:
I'd like to avoid having to use such a big thing as an int128 (that would be the 64 bits of FileReferenceNumber + 5 bits for the drive letter C:, D:, E:, ..., Z:).
I also would like to avoid having to use a pair (char DriveLetter, DWORDLONG FileReferenceNumber) to identify a file in the computer.
How to use a 64-bit int to code FileReferenceNumber + drive letter?
Is it possible because FileReferenceNumber has a few free unused bits?
If not, how would you handle this?
You must use a pair of FileReferenceNumber/FileID and "volume something". You can mount a volume in a folder so you cannot really use the drive letter.
Ideally "volume something" is the volume GUID path but you can use the volume serial number if size is important. Note: Not all volumes have a GUID.
For NTFS you can get it from GetFileInformationByHandle and build a 32-bit+64-bit pair. For ReFS you need GetFileInformationByHandleEx and build a 64-bit+128-bit pair.