[rogerbinns]

There are various arbitrary restrictions in various filesystems and operating systems. The intention is to store smaller amounts of useful information with the file. Smaller means in the bytes/kilobytes range. For example you wouldn't store multi-gigabyte alternate language versions of a video file in its extended attributes. But you could store URLs of where to get them.

Or you could attach authorship, review, dates, keywords and similar metadata which would work for any file type, not just those whose format explicitly has that support.

If you want to get a handle on what filesystem design is like then I highly recommend Dominic Giampaolo's book on the design and implementation of the Be filesystem (he wrote BeFS). The book is freely available from his website as http://www.nobius.org/~dbg/practical-file-system-design.pdf and includes information about the design of other filesystems too. It isn't exhaustive, but does give a very good grounding in filesystems and does cover extended attributes.

[stefantalpalaru]

Thanks for the recommendation, that book looks interesting.