Re: [9fans] FS question

[Geoff Collyer <geoff@collyer.net>]

I didn't use the original Unix file system, but the V6-era (ca. 1975)
one was simple yet provided substantial utility.  The main uses of
links that I can recall were locking and renaming.  Linking to an
agreed-upon name was atomic and formed the basis for most locking by
cooperating processes before things like lockf and flock (and
eventually the 'l' bit).

Renaming was done by linking from the old name to the new, then
removing the old name (if the link succeeded).  This even worked for
directories (adding some fiddling with ..  entries) and let one move
files and directories anywhere within a given file system's directory
tree.  The modern (Berkeley) rename() primitive is by contrast very
difficult to get right, taking into account races and potential errors
of various sorts.  The one thing that links permitted and that I miss
in Plan 9 is being able to efficiently move directories arbitrarily
within a file system, though it's less of an issue than on Unix, where
shuffling directory hierarchies was the vendors' and standards bodies'
equivalent of corporate reorganisation (i.e., we'll rename everything
and hope that nobody notices that we haven't done much else).