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From: Bill Davidsen <>
To: Jan Engelhardt <>
Cc: Andi Kleen <>,
	Jasper Bryant-Greene <>,
	rzryyvzy <>,
Subject: Re: Is there a "blackhole" /dev/null directory?
Date: Fri, 15 Feb 2008 14:25:55 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <Pine.LNX.4.64.0802141553400.694@fbirervta.pbzchgretzou.qr>

Jan Engelhardt wrote:
> On Feb 14 2008 10:46, Andi Kleen wrote:
>> Jasper Bryant-Greene <> 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.

Also: to let a program believe it was creating files which are used to 
hold the written data. Otherwise /dev/null would probably be the solution.
> 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".

I think what is going to happen is that files created behave as if they 
are the result of a mknod resulting in a /dev/null clone.
> 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.

The directory structure can persist, it's the writing of data which can 
be avoided.

Real example:

A program which reads log files and prepares a whole raft of reports in 
a directory specified. If you just want to see the summary (stdout) and 
exception notices (stderr) having a nulldir would avoid the disk space 
and i/o load if you were just looking at the critical output rather than 
the analysis.

Yes, if this was an original program requirement it would or should have 
been a feature. Real world cases sometimes use tools in creative ways.

Bill Davidsen <>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

  parent reply	other threads:[~2008-02-15 19:24 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-14  9:30 rzryyvzy
2008-02-14  9:39 ` Jasper Bryant-Greene
2008-02-14  9:46   ` Andi Kleen
2008-02-14 15:00     ` Jan Engelhardt
2008-02-14 15:19       ` Hans-Jürgen Koch
2008-02-14 15:23         ` Jan Engelhardt
2008-02-14 15:30           ` Hans-Jürgen Koch
2008-02-15 19:25       ` Bill Davidsen [this message]
2008-02-14 12:16   ` Mika Lawando
2008-02-14 15:06     ` linux-os (Dick Johnson)
     [not found] <>
2008-02-14 17:16 ` Bodo Eggert
     [not found] ` <>
     [not found]   ` <>
     [not found]     ` <>
     [not found]       ` <>
2008-02-15  1:15         ` Bodo Eggert

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