From: Shaya Potter <spotter@cs.columbia.edu>
To: Valdis.Kletnieks@vt.edu
Cc: John Bradford <john@grabjohn.com>,
Alan Cox <alan@lxorguk.ukuu.org.uk>,
root@chaos.analogic.com, Frank Davis <fdavis@si.rr.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: kernel support for non-english user messages
Date: 11 Apr 2003 00:23:16 -0400 [thread overview]
Message-ID: <1050034996.23950.21.camel@zaphod> (raw)
In-Reply-To: <200304110419.h3B4JeBm004315@turing-police.cc.vt.edu>
yes, yes. I of course agree, just saying that if someone really wanted
to do it, banging out a skeleton solution that can be filled in
shouldn't be "that" hard. Getting it "right"(tm) would be tougher, but
I think doable. The reason I think no one has done it, is because no
one is really that interested.
On Fri, 2003-04-11 at 00:19, Valdis.Kletnieks@vt.edu wrote:
> On Thu, 10 Apr 2003 18:20:15 EDT, Shaya Potter said:
> > On Thu, 2003-04-10 at 16:36, John Bradford wrote:
> > > > There is a lot of anti-VMS stuff in the Unix world mostly coming
> > > > from the _horrible_ command line and other bad early memories. There
> > > > is also a hell of a lot of really cool stuff under that command line
> > > > we could and should learn from.
> > >
> > > When are we going to see versioned filesystems in Linux? That was a
> > > standard feature in VMS.
> >
> > it shouldn't be that hard, it was one of the 6 OS projects for the
> > regular 4000 level (senior/grad) level OS class here at columbia last
> > semster.
> >
> > The assignment was to modify ext2 to support versioning, basically means
> > making a copy of it within ext2's open, if it's opened O_RDWR. The
> > assignment was a little bit more complicated in that we took an ext2
> > flag bit to mean "version", so that a file would only be versioned if
> > the bit was set, as well as only allowing a single level of versioning,
> > though extending it w/ more wouldn't be that hard.
> >
> > The student solutions (as well as our sample solution) weren't that
> > "pretty", but then again, each project was only for 2-2.5 weeks.
>
> The problem is, as usual, in the details that almost never get handled in 2-week
> student projects. Some off the top of my head:
>
> 1) What happens when *multiple* programs have a file open at the same time?
> If you only handle one level of versioning, somebody is going to lose. Handling
> multiple levels is of course more "fun". And you get to worry about race
> conditions - does your code DTRT if multiple processes do an open() on alternate
> CPUs at the same time. Does it DTRT if a process open()s a file, and then fork()s,
> and both parent and child start scribbling on the file descriptor?
>
> 2) For that matter, should new versions be created at open() or at the first write()?
> Doing it at write() allows not creating a new version if no changes have
> actually happened - but this has its own issues.
>
> 3) Version a 500 megabyte file. Change one block. Do it a few more times.
> Are you better off copying the whole file (which bloats your disk usage and
> kills your I/O bandwidth), or keeping deltas (the list of allocated blocks could be
> almost identical except for the replaced/rewritten blocks). However, this DOES
> make doing an fsck() a *lot* more interesting - is a block allocated to multiple
> files in error or not?
>
> 4) What happens if you rename() a file? Can you open() a previous version for
> writing? If so, does it get versioned? How does a backup program restore a
> previous version?
>
> 5) Let's say we use VMS-style filenames to version. foo, foo;2, foo;3, etc.
> Now, is open("foo;2",...) a reference to the previous version of foo or to a new
> file that happens to be called foo;2? What happens if some other file happens
> to be called foo;2 and you create a version of foo?
>
> 6) OK, since anything besides \0 and / is legal in a filename, we can't use ;N to
> version. Let's steal another field in the inode to do the counting. Now how does
> userspace reference a previous version easily? Can you get into a situation where
> different versions of a file have different owners/permissions?
>
> 7) Userspace support. Anybody want to open that can and take up worm farming? ;)
>
> 8) User support issues. See (7). ;)
>
> That's just the first 10 minutes or so of thinking about things that could be problems
> that a student project won't address.
>
> Yes, VMS had to worry about a lot of these issues too - but VMS had the advantage that
> versioning was designed into the environment from very early on, and wasn't a retrofit
> as it would be for Linux. So they could make arbitrary rules like "If there's a
> ;nnn on the end of a filename, it's a version" without having to worry about breaking
> anything.
next prev parent reply other threads:[~2003-04-11 4:14 UTC|newest]
Thread overview: 137+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-04-09 5:02 kernel support for non-english user messages Frank Davis
2003-04-09 5:29 ` Oliver Neukum
2003-04-09 5:50 ` Frank Davis
2003-04-09 9:37 ` Bernd Petrovitsch
2003-04-09 11:04 ` Alan Cox
2003-04-09 5:53 ` Andreas Dilger
2003-04-09 8:08 ` Matti Aarnio
2003-04-09 9:33 ` Oliver Neukum
2003-04-09 10:24 ` Matti Aarnio
2003-04-09 22:07 ` Werner Almesberger
2003-04-09 22:41 ` Frank Davis
2003-04-09 22:55 ` Ulrich Drepper
2003-04-09 23:53 ` Johannes Ruscheinski
2003-04-10 1:43 ` Richard B. Johnson
2003-04-10 18:57 ` Alan Cox
2003-04-10 20:13 ` Trond Myklebust
2003-04-10 19:42 ` Alan Cox
2003-04-11 0:48 ` Christer Weinigel
2003-04-11 15:56 ` Daniel Stekloff
2003-04-10 20:53 ` Richard B. Johnson
2003-04-10 23:05 ` Jon Portnoy
2003-04-11 5:39 ` DevilKin
2003-04-11 5:49 ` Arnaldo Carvalho de Melo
2003-04-11 6:17 ` DevilKin
2003-04-11 17:51 ` Randy.Dunlap
2003-04-11 11:57 ` Helge Hafting
2003-04-11 17:55 ` David Lang
2003-04-10 20:36 ` John Bradford
2003-04-10 22:20 ` Shaya Potter
2003-04-11 4:19 ` Valdis.Kletnieks
2003-04-11 4:23 ` Shaya Potter [this message]
2003-04-11 8:40 ` Henning P. Schmiedehausen
2003-04-11 9:09 ` John Bradford
2003-04-11 10:59 ` Valdis.Kletnieks
2003-04-11 11:11 ` John Bradford
2003-04-11 11:40 ` Helge Hafting
2003-04-24 23:25 ` versioned filesystems in linux (was Re: kernel support for non-english user messages) Stewart Smith
2003-04-25 7:14 ` John Bradford
2003-04-25 15:20 ` Matthew Sell
2003-04-25 15:45 ` Richard B. Johnson
2003-04-25 16:18 ` versioned filesystems in linux (was Re: kernel support for John Bradford
2003-04-25 17:06 ` Richard B. Johnson
2003-04-25 17:48 ` Valdis.Kletnieks
2003-04-25 19:38 ` H. Peter Anvin
2003-04-25 21:21 ` 9-track tape drive (Was: Re: versioned filesystems in linux) John Bradford
2003-04-25 21:22 ` H. Peter Anvin
2003-04-25 21:31 ` Mike Dresser
2003-04-26 6:32 ` H. Peter Anvin
2003-04-26 6:57 ` John Bradford
2003-04-25 18:13 ` versioned filesystems in linux (was Re: kernel support for John Bradford
2003-04-25 18:34 ` Richard B. Johnson
2003-04-10 8:19 ` kernel support for non-english user messages Oliver Neukum
2003-04-09 13:11 ` Giuliano Pochini
2003-04-10 3:08 ` Linus Torvalds
2003-04-10 9:05 ` kernel support for non-English " Riley Williams
2003-04-10 17:35 ` Linus Torvalds
2003-04-10 18:32 ` John Bradford
2003-04-12 2:55 ` Chris Wedgwood
2003-04-09 19:01 kernel support for non-english " Perez-Gonzalez, Inaky
2003-04-09 19:25 Perez-Gonzalez, Inaky
2003-04-09 23:31 Jim Keniston[UNIX]
2003-04-10 19:01 ` Alan Cox
2003-04-11 9:21 ` kernel support for non-English " Riley Williams
2003-04-11 12:16 ` Alan Cox
2003-04-11 13:39 ` John Bradford
2003-04-11 13:11 ` Alan Cox
2003-04-11 14:48 ` John Bradford
2003-04-10 10:47 kernel support for non-english " Ruth Ivimey-Cook
2003-04-10 19:21 Perez-Gonzalez, Inaky
2003-04-10 20:41 ` Robert White
2003-04-11 9:21 ` kernel support for non-English " Riley Williams
2003-04-11 20:49 ` Robert White
2003-04-11 22:53 ` Riley Williams
2003-04-15 3:44 ` Robert White
2003-04-15 11:08 ` Alan Cox
2003-04-15 11:08 ` Alan Cox
2003-04-15 14:07 ` Timothy Miller
2003-04-11 21:04 ` Ruth Ivimey-Cook
2003-04-11 21:31 ` Daniel Stekloff
2003-04-10 20:54 kernel support for non-english " Chuck Ebbert
2003-04-10 21:08 ` Bernd Petrovitsch
2003-04-10 21:20 Perez-Gonzalez, Inaky
2003-04-10 22:06 ` Andreas Dilger
2003-04-11 7:38 ` Ville Herva
2003-04-10 22:13 Chuck Ebbert
2003-04-10 22:33 ` Stephen Hemminger
2003-04-10 23:23 Chuck Ebbert
2003-04-11 10:10 Chuck Ebbert
[not found] <20030409051006$1ecf@gated-at.bofh.it>
[not found] ` <20030409081011$5257@gated-at.bofh.it>
[not found] ` <20030409221017$6c98@gated-at.bofh.it>
[not found] ` <20030409225009$2558@gated-at.bofh.it>
[not found] ` <20030410014009$78fb@gated-at.bofh.it>
[not found] ` <20030410200019$3e8f@gated-at.bofh.it>
[not found] ` <20030410202016$7d48@gated-at.bofh.it>
2003-04-11 11:29 ` Tim Connors
2003-04-11 13:17 kernel support for non-English " Chuck Ebbert
2003-04-11 13:40 ` John Bradford
2003-04-16 1:59 ` Gerrit Huizenga
2003-04-16 14:28 ` Timothy Miller
2003-04-16 14:37 ` Alan Cox
2003-04-16 16:20 ` Timothy Miller
2003-04-16 17:04 ` Bruce Harada
2003-04-16 18:34 ` Timothy Miller
2003-04-16 18:37 ` Bruce Harada
2003-04-11 14:37 ` Richard B. Johnson
2003-04-11 16:00 ` Linus Torvalds
2003-04-12 8:22 ` Kai Henningsen
2003-04-12 11:08 ` John Bradford
2003-04-11 14:52 Paolo Ciarrocchi
2003-04-11 16:57 Chuck Ebbert
2003-04-11 17:38 ` Richard B. Johnson
2003-04-11 18:10 ` Matti Aarnio
2003-04-11 20:02 kernel support for non-english " Perez-Gonzalez, Inaky
[not found] <A46BBDB345A7D5118EC90002A5072C780BEBA7DD@orsmsx116.jf.inte l.com>
2003-04-11 20:55 ` Ruth Ivimey-Cook
2003-04-11 22:21 kernel support for non-English " Chuck Ebbert
2003-04-11 22:53 ` Martin J. Bligh
2003-04-12 7:55 ` John Bradford
2003-04-12 7:48 ` John Bradford
2003-04-14 11:40 ` Denis Vlasenko
2003-04-14 12:55 ` John Bradford
2003-04-14 17:29 ` Linus Torvalds
2003-04-14 18:15 ` John Bradford
2003-04-14 23:04 ` Felipe Alfaro Solana
2003-04-15 13:21 ` Alex Combas
2003-04-15 18:02 ` Eric Altendorf
2003-04-17 13:46 ` Alan Cox
2003-04-17 15:07 ` Randolph Bentson
2003-04-17 18:49 ` Eric Altendorf
2003-04-14 13:18 ` Sean Neakums
2003-04-14 14:23 ` Valdis.Kletnieks
2003-04-16 5:03 ` Denis Vlasenko
2003-04-11 23:36 Jim Keniston[UNIX]
2003-04-11 23:38 Chuck Ebbert
2003-04-12 9:52 Chuck Ebbert
2003-04-12 15:20 Chuck Ebbert
2003-04-12 15:34 ` Alan Cox
2003-04-12 17:22 ` Robert P. J. Day
2003-04-13 3:59 ` Martin J. Bligh
2003-04-13 6:21 ` John Bradford
2003-04-12 16:47 Chuck Ebbert
2003-04-12 20:31 Chuck Ebbert
2003-04-14 9:07 ` Denis Vlasenko
2003-04-14 21:27 Chuck Ebbert
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