Re: silent semantic changes with reiser4

Linus Torvalds
2004-08-25T21:00:01Z

On Wed, 25 Aug 2004 viro@parcelfarce.linux.theplanet.co.uk wrote:
>
> On Wed, Aug 25, 2004 at 01:22:55PM -0700, Linus Torvalds wrote:
> >
> > It's the UNIX way.
>
> Not if you allow link(2) on them.

Heh. I don't think that's a very strong argument against being "unixy",
considering how traditional unix _used_ to handle directories.

mkdir/rmdir/rename only came later. Now, obviously they did come later for
a good reason, but still..

The interesting part is that thanks to the dcache, we should be perfectly
able to actually _see_ circular links etc, so some of the problems with
linking directories should actually be quite solvable - something that is
_not_ true for a traditional UNIX VFS layer.

Of course, the dcache introduces some new problems of its own wrt
directory aliasing, but I don't actually think that should be fundamental
either. Treating them more as a "static mountpoint" from an FS angle and
less as a traditional Unix hardlink should be doable, I'd have thought.

(Also, it's entirely possible that the filesystem may not support some of
the more esoteric linking/renaming operations. For example, in a
traditional xattrs setup where the xattr is linked on-disk with the file
it is associated with, you simply _can't_ link it somewhere else, or
rename it to any other directory. That's not a VFS layer issue, obviously,
but I thought I'd bring up the point that file-as-dir cases may have
limitations that normal files don't have).

> And not if you design and market your stuff as a general-purpose
> backdoor into kernel.

Now that's a separate argument, and not one I'm personally interested in
arguing at least right now. I haven't actually looked at the reiser4 code,
so I'm really _only_ arguing against special-case attributes.

Linus