From: Jay Logue via TUHS <tuhs@minnie.tuhs.org>
To: tuhs@minnie.tuhs.org
Subject: Re: [TUHS] moving directories in svr2
Date: Wed, 29 Dec 2021 19:40:57 -0800 [thread overview]
Message-ID: <20211230034805.6CC299CD62@minnie.tuhs.org> (raw)
In-Reply-To: <20211229193348.A4ED018C08E@mercury.lcs.mit.edu>
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v6 mv is indeed limited to renaming directories. However, mv on v7 is
able to move directories. Considering the similarity between the code
bases, I think it would be fairly straightforward to support directory
move on v6 in the same manner as was done in v7. (On a related tangent,
I found it fairly straightforward to implement modern rename(2)
semantics on top of both code bases in my retro-fuse filesystem [e.g.
v6fs.c:559
<https://github.com/jaylogue/retro-fuse/blob/b300865c1aa4c38930adea66de364f182c73b3b5/src/v6fs.c#L599>].
Of course I had the benefit of a single-threaded execution environment.)
Given the way mkdir and directory renaming worked in v6/v7, I'm not sure
the lack of atomicity in directory move would have made things any worse
for operators. It's interesting though that dcheck does not look for
malformed directory links.
--Jay
On 12/29/2021 11:33 AM, Noel Chiappa wrote:
> > From: Clem Cole
>
> > Try it on V6 or V7 and you will get 'directory exists' as an error.
>
> The V6 'mv' is prepared to move a directory _within_ a directory (i.e.
> 'rename' functionality). I'm not sure why it's not prepared to move within
> a partition; probably whoever wrote it wasn't prepared to deal with all the
> extra work for that (unlink from the old '..', then link to the '..' in the
> new directory, etc, etc).
>
> (The MIT PWB1 had a 'mvdir' written by Jeff Schiller, so PWB1 didn't have
> 'move directory' functionality before that. MIT must have been using the PWB1
> system for 6.031, which I didn't recall; the comments in 'mvdir' refer to it
> being used there.)
>
> The V6 'mv' is fairly complicated (as I found out when I tried to modify it
> to use 'smdate()', so that moving a file didn't change its 'last write'
> date). Oddly enough, it is prepared to do cross-partition 'moves' (it forks a
> 'cp' to do the move). Although on V6, 'cp' only does one file; 'cp *.c
> {dest}' was not supported, there was 'cpall' for that. (Why no 'mvall', I
> wonder? It would have been trivial to clone 'cpall'.)
>
> Run fact; the V6 'mv' is the place that has the famous (?) "values of B will
> give rise to dom!" error message (in the directory-moing section).
>
> > if the BSD mv command for 4.1 supported it. If it did then it was not
> > atomic -- it would have had to create the new directory, move the
> > contents independently and then remove the old one.
>
> Speaking of atomic operation, in V6 'mkdir' (not being a system call) was
> not atomic, so if interrupted at 'just the right time', it could leave
> the FS in an inconsistent state. That's the best reason I've come across
> to make 'mkdir' a system call - it can be made atomic that way.
>
> Noel
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next prev parent reply other threads:[~2021-12-30 3:48 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-29 19:33 Noel Chiappa
2021-12-30 3:40 ` Jay Logue via TUHS [this message]
-- strict thread matches above, loose matches on Subject: below --
2021-12-30 3:45 Noel Chiappa
2021-12-30 4:02 ` Bakul Shah
2021-12-30 16:40 ` Theodore Ts'o
2021-12-30 22:31 ` Dan Cross
2021-12-31 0:43 ` Bakul Shah
2021-12-31 1:00 ` Rob Pike
2021-12-31 1:45 ` Bakul Shah
2021-12-31 2:23 ` Adam Thornton
2021-12-31 18:56 ` Chet Ramey
2021-12-31 3:08 ` Theodore Ts'o
2021-12-31 3:23 ` Rob Pike
2021-12-31 5:16 ` Theodore Ts'o
2021-12-31 5:21 ` Dan Cross
2021-12-31 5:55 ` Rob Pike
2021-12-31 13:32 ` Michael Kjörling
2021-12-31 15:53 ` Adam Thornton
2021-12-31 16:13 ` Arthur Krewat
2021-12-31 18:17 ` Dan Cross
2021-12-31 18:23 ` Larry McVoy
2021-12-31 18:37 ` Dan Cross
2021-12-31 18:29 ` Arthur Krewat
2022-01-01 0:09 ` Theodore Ts'o
2022-01-03 13:35 ` Dan Cross
2022-01-03 20:23 ` Theodore Ts'o
2022-01-03 20:45 ` Warner Losh
2022-01-03 21:15 ` Dan Cross
2022-01-03 22:26 ` Theodore Ts'o
2022-01-03 23:10 ` Dan Cross
2022-01-04 15:45 ` Chet Ramey
2022-01-09 19:28 ` Larry McVoy
2022-01-03 23:21 ` Doug McIntyre
2022-01-03 23:37 ` Adam Thornton
2022-01-04 14:49 ` Stuart Remphrey
2022-01-03 23:44 ` Larry McVoy
2022-01-03 23:56 ` Warner Losh
2022-01-04 2:28 ` Theodore Ts'o
2022-01-04 2:42 ` Larry McVoy
2022-01-03 22:57 ` Phil Budne
2021-12-31 5:12 ` Bakul Shah
2021-12-29 19:13 Douglas McIlroy
2021-12-29 19:37 ` Dan Cross
2021-12-29 20:15 ` Dan Cross
2021-12-29 20:42 ` Richard Salz
2021-12-29 20:58 ` Dan Cross
2021-12-29 21:20 ` Clem Cole
2021-12-30 3:15 ` Bakul Shah
2021-12-29 17:12 Douglas McIlroy
2021-12-29 16:59 Bakul Shah
2021-12-29 17:04 ` Clem Cole
2021-12-29 17:14 ` arnold
2021-12-29 17:38 ` Clem Cole
2021-12-29 17:49 ` Brantley Coile
2021-12-29 18:27 ` ron minnich
2021-12-29 20:59 ` Rob Pike
2021-12-29 14:33 Will Senn
2021-12-29 15:02 ` arnold
2021-12-29 15:38 ` Will Senn
2021-12-29 15:44 ` Richard Salz
2021-12-29 16:17 ` Clem Cole
2021-12-29 16:58 ` Richard Salz
2021-12-30 5:14 ` Dan Stromberg
2021-12-30 16:22 ` Clem Cole
2021-12-30 18:02 ` John Cowan
2021-12-30 23:04 ` Richard Salz
2021-12-29 15:17 ` Clem Cole
2021-12-29 15:44 ` Will Senn
2021-12-29 16:10 ` Clem Cole
2021-12-29 16:33 ` Warner Losh
2021-12-29 16:01 ` Bakul Shah
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