[mappu]

It's easy to forget about supporting EAs on Windows - they are extremely uncommon because you practically need to be in kernelspace to write them. Ntoskrnl.exe has one or two EAs, almost nothing else does.

(ADS are super commonplace and the closer analogue to posix xattrs.)

[qwerty456127]

I didn't know this, thanks. I thought xattrs and ADS are synonymous. Do SquashFS, ext4, HFS+ and APFS have ADS then?

I am looking forward to write my own cross-platform app which would rely on attaching additional data and metatata to my files.

"need to be in kernelspace" does not sound very scary because a user app probably doesn't need to do this very job itself - isn't there usually an OS-native command-line tool which can be invoked to do it?