linux-kernel - Re: Is there a "blackhole" /dev/null directory?

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Date:	Thu, 14 Feb 2008 16:30:01 +0100
From:	Hans-Jürgen Koch <hjk@...utronix.de>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Jasper Bryant-Greene <jasper@...x.geek.nz>,
	rzryyvzy <rzryyvzy@...shmail.net>, linux-kernel@...r.kernel.org
Subject: Re: Is there a "blackhole" /dev/null directory?

Am Thu, 14 Feb 2008 16:23:37 +0100 (CET)
schrieb Jan Engelhardt <jengelh@...putergmbh.de>:

> 
> On Feb 14 2008 16:19, Hans-Jürgen Koch wrote:
> >> 
> >> Q: What if a program attempts to mkdir /dev/nullmnt/foo to just
> >>    create a file /dev/nullmnt/foo/barfile?
> >> A: /dev/nullmnt/foo must continue to exist or be accepted for a
> >> while, or perhaps for eternity.
> >
> >Well, the problem seems to be that a "directory" is not just data but
> >also contains metadata. While it's easy to write data to /dev/null,
> >you cannot simply discard metadata associated with a directory. So,
> >such a "/dev/null-directory" would have to remember metadata (at
> >least all created filenames including subdirectories) in the same
> >way as other filesystems do. Only file _content_ can be discarded.
> 
> Not even that. Suppose a userspace program (whose output you'd like
> to discard) does:

[...]

Well, if an application wants to read back written data, you can never
use such a thing, not even in simple cases where the
existing /dev/null would be enough. 

> }
> 
> >To be honest, I still cannot see many sensible usecases for that...
> 
> I agree.

Good :-)

Hans
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