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Message-ID: <47B5E743.3000101@tmr.com>
Date: Fri, 15 Feb 2008 14:25:55 -0500
From: Bill Davidsen <davidsen@....com>
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?
Jan Engelhardt wrote:
> On Feb 14 2008 10:46, Andi Kleen wrote:
>> Jasper Bryant-Greene <jasper@...x.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.
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 <davidsen@....com>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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