Date: Sat, 13 Mar 2004 22:03:05 +0100
From: Pavel Machek <pavel@ucw.cz>
To: =?iso-8859-1?Q?J=F6rn?= Engel <joern@wohnheim.fh-wedel.de>
Cc: Sytse Wielinga <s.b.wielinga@student.utwente.nl>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH for testing] cow behaviour for hard links
Message-ID: <20040313210305.GB549@elf.ucw.cz>
References: <20040310193429.GB4589@wohnheim.fh-wedel.de> <200403121849.03505.s.b.wielinga@student.utwente.nl> <20040312182912.GB7087@wohnheim.fh-wedel.de> <20040313134330.GC3352@openzaurus.ucw.cz> <20040313194827.GA4748@wohnheim.fh-wedel.de>
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20040313194827.GA4748@wohnheim.fh-wedel.de>
User-Agent: Mutt/1.5.4i
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1563
Lines: 43

On So 13-03-04 20:48:27, J?rn Engel wrote:
> On Sat, 13 March 2004 14:43:30 +0100, Pavel Machek wrote:
> > 
> > I do not know your current design, but...
> > 
> > In ideal world there would be no COW links. System would
> > magically detect that you are doing cp -a, and would link
> > at individual block level.
> >
> > Well, that would be probably too fs-specific. But introducing copyfile()
> > syscall, which would just link the inodes if underlying fs
> > supported it might be good start. On first
> > write into one
> > of linked files copy
> > would be done...
> 
> Agreed.
> 
> > Only disadvantage I see is that such links would not survive
> > tar-backup...
> 
> That's not a problem either.  Have a userspace program that checks all
> files and hints for identical ones (new syscall, copyfile() cannot do
> this without races).  Depending on fs size, the necessary data can
> grow into the gigabytes, but the code is just 200 lines.

Hmm, I don't quite like "copyfile if not modified" syscall, but even
without that it is usefull...

> Or did you mean the problem of tar backups growing *much* larger than
> the real filesystem?  Yes, tar becomes useless for backups then. :)

Yep, this is what I meant.
								Pavel

-- 
When do you have a heart between your knees?
[Johanka's followup: and *two* hearts?]
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/