Date: Thu, 14 Feb 2008 16:00:06 +0100 (CET)
From: Jan Engelhardt <jengelh@computergmbh.de>
To: Andi Kleen <andi@firstfloor.org>
cc: Jasper Bryant-Greene <jasper@unix.geek.nz>,
       rzryyvzy <rzryyvzy@trashmail.net>, linux-kernel@vger.kernel.org
Subject: Re: Is there a "blackhole" /dev/null directory?
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On Feb 14 2008 10:46, Andi Kleen wrote:
>Jasper Bryant-Greene <jasper@unix.geek.nz> writes:
>>
>> This could be done fairly trivially with FUSE, and IMHO is a good use
>> for FUSE because since you're just throwing most data away, performance
>> is not a concern.

There is a much more interesting 'problem' with a "/dev/null directory".

Q: Why would you need such a directory?
A: To temporarily fool a program into believing it wrote something.

Q: Should all files disappear? (e.g. "unlink after open")
A: Maybe not, programs may stat() the file right afterwards and
   get confused by the "inexistence".

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.

Been there, done that, -
http://dev.computergmbh.de/wsvn/misc_kernel/nullfs/trunk/nullfs.c -
and hit that wall of unanswerable questions.
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