Re: [9fans] mv vs cp

[Alexander Viro <viro@math.psu.edu>]

On Tue, 9 Oct 2001, Thomas Bushnell, BSG wrote:

> It's adequate to do this on a per-filesystem basis (assuming you
> prohibit cross-device renames), so the Hurd can conveniently do it in

BTDT (see fs/namei.c::vfs_rename_dir() in Linux 2.4.x).  But that's far
from the only annoying piece of shit in rename(2) semantics.  E.g. you
are getting very ugly locking rules if you want to handle the case of
rename() removing an empty directory correctly.

Again, I've really been there and done that.  It wasn't pretty and I
would be much happier if rename() couldn't change the topology.  We
couldn't do that since it would break a lot of userland stuff;  Plan 9
has a luxury of dropping annoying crap and being able to find and fix
resulting breakage in userland.  In this case crap is not there in the
first place, so introducing it would cause a lot of ugliness in the kernel
for no good reason.

> individual servers (and does); Plan 9 could do the same I would
> suspect.

I suspect that Hurd has slightly, erm, different design philosophy (and
that's about the only printable comment I can make on the thing, so let's
not go there).