linux-kernel - Re: Finding hardlinks

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Message-ID: <Pine.LNX.4.64.0701032009140.6871@artax.karlin.mff.cuni.cz>
Date:	Wed, 3 Jan 2007 20:17:34 +0100 (CET)
From:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
To:	Frank van Maarseveen <frankvm@...nkvm.com>
Cc:	Jan Harkes <jaharkes@...cmu.edu>, Pavel Machek <pavel@...e.cz>,
	Arjan van de Ven <arjan@...radead.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Finding hardlinks



On Wed, 3 Jan 2007, Frank van Maarseveen wrote:

> On Tue, Jan 02, 2007 at 01:04:06AM +0100, Mikulas Patocka wrote:
>>
>> I didn't hardlink directories, I just patched stat, lstat and fstat to
>> always return st_ino == 0 --- and I've seen those failures. These failures
>> are going to happen on non-POSIX filesystems in real world too, very
>> rarely.
>
> I don't want to spoil your day but testing with st_ino==0 is a bad choice
> because it is a special number. Anyway, one can only find breakage,
> not prove that all the other programs handle this correctly so this is
> kind of pointless.
>
> On any decent filesystem st_ino should uniquely identify an object and
> reliably provide hardlink information. The UNIX world has relied upon this
> for decades. A filesystem with st_ino collisions without being hardlinked
> (or the other way around) needs a fix.

... and that's the problem --- the UNIX world specified something that 
isn't implementable in real world.

You can take a closed box and say "this is POSIX cerified" --- but how 
useful such box could be, if you can't access CDs, diskettes and USB 
sticks with it?

Mikulas
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