Not an answer, but relevant: Apple's Time Machine works by hard-linking directories to make the forest of old roots.


On Thu, Dec 30, 2021 at 5:28 AM ron minnich <> wrote:
since .. came up, nobody mentioned it yet,

but the subject line is "moving directories" and, as pointed out, on
old school file systems with hard links, it's not a move, just an ln,
more or less. And in the easy case, it's easy; and in the not so easy
case, it can be impossible ...

On newer systems, which don't have such notions as hard links, it's a
different game, and on many, it may not be possible; dircp to the
rescue, with all the pain that implies (doesn't go well when you are
in CA and the server is in NJ, trust me :-)

But this brings up a question I forgot: what was the last Unix version
that let users make arbitrary links, such that the file system was no
longer a DAG? I recall in v6 days hearing that earlier Unix allowed
this, and that cleanup (via icheck and friends) got to be near

On Wed, Dec 29, 2021 at 9:50 AM Brantley Coile <> wrote:
> Plan 9 can't move directories with mv. I will only change the name of them.
> (If this is the question. I was only half paying attention to the thread. Sorry)
>         --bwc
> cessna% mkdir dira
> cessna% mkdir dirb
> cessna% touch dira/a
> cessna% touch dirb/b
> cessna% mv dira dirb
> mv: can't remove ./dirb: remove -- directory not empty
> To move contents of directories we use dircp.
> cessna% man dircp
>      TAR(1)                                                     TAR(1)
>      NAME
>           tar, dircp - archiver
>           tar key [ file ... ]
>           dircp fromdir todir
>           Tar saves and restores file trees.  It is most often used to
>           transport a tree of files from one system to another.  The
>         ...
>                and .tz.  If no extension matches, gzip is used.  The z
>                flag is unnecessary (but allowed) when using the t and
>                x verbs on archives with recognized extensions.
>           Tar can be used to copy hierarchies thus:
>                @{cd fromdir && tar c .} | @{cd todir && tar xT}
>           Dircp does this.
>      SOURCE
>           /sys/src/cmd/tar.c
>           /rc/bin/dircp
>      SEE ALSO
>           ar(1), bundle(1), tapefs(4), mkfs(8)
> cessna%
> > On Dec 29, 2021, at 12:38 PM, Clem Cole <> wrote:
> >
> > At the risk of kicking a dead horse too much ...
> >
> > On Wed, Dec 29, 2021 at 12:14 PM <> wrote:
> > Plan 9 eventually did something like this. I don't remember the details.
> > Arnold - point taken but ... unfortunately, I think that the comparison is a little difficult because Plan9's concepts of namespaces is a tad different than UNIX's.  But I'll let Rob or Ken comment as they lived and developed both systems.
> >
> > FWIW: An object store is something that retains information after the processes that operates on it complete - i.e. its a static entity.  Links were (are) also a static concept.   Late binding to names (like symlinks) are a dynamic (runtime idea).  Bakul points out that by using the per process u area, the dynamic context can be retained.  The observation is that .. (like symlinks) tend to be a runtime (dynamic) notion, although I'm not sure how you keep consistency in the static FS if you don't store the link in the inode.  As someone that did, I suggest - try writing fsck if you are using dynamic content.   How do you know?  I'd still claim it is the same issue.
> >
> > Anyway, I suppose that like context sensitive symlinks (which I sorely miss), you could do this and keep a list of the N inodes for the N parents and then like CDSL's keep the one you used to get there in the u area so that .. picks the proper one on the way out and you can still have the static notion which something like fsck can check off line.