30 Dec
2021
30 Dec
'21
12:27 a.m.
since .. came up, nobody mentioned it yet, https://plan9.io/sys/doc/lexnames.pdf
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
impossible.
On Wed, Dec 29, 2021 at 9:50 AM Brantley Coile <brantley(a)coraid.com> 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
SYNOPSIS
tar key [ file ... ]
dircp fromdir todir
DESCRIPTION
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.
EXAMPLES
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
<clemc(a)ccc.com> wrote:
At the risk of kicking a dead horse too much ...
On Wed, Dec 29, 2021 at 12:14 PM <arnold(a)skeeve.com> 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.