I noticed Dropbox started setting their own xattrs on my files a year or two ago if I recall correctly.

My guess at the time was that they were using it for cheaper rename detection, using an xattr UUID, instead of using heuristics to compare {inode, btime, mtime, size, name, folder}.

In other words, they would match up the xattr UUID across CREATE and DELETE events to merge them into RENAME events.

Missing RENAME events is pretty bad for the user experience as it can lead to a loss of version history when the file ID changes through the DELETE, CREATE events.

Anyone have any other ideas as to why they would be reliant on xattrs?