Filesystems, by design, hide a lot of complexity from users. At times,
though, those users need to be able to look inside the black box and extract
information about what is going on within a filesystem. Answering this
need is David Howells, the creator of a number of filesystem-oriented
system calls; in this
patch set he tries to add three more, one of which we have seen before
and two of which are new.

Source: LWN.net – [$] watch_mount(), watch_sb(), and fsinfo() (again)