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Subject: Re: Is there a "blackhole" /dev/null directory?
Date: Thu, 14 Feb 2008 10:06:33 -0500
Message-ID: <Pine.LNX.4.61.0802140952550.1324@chaos.analogic.com>
In-Reply-To: <47B43138.40206@trashmail.net>
Thread-Topic: Is there a "blackhole" /dev/null directory?
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References: <20080214093051.7240852AB0E31@trashmail.net> <1202981957.10928.17.camel@phobos.jasper.bg> <47B43138.40206@trashmail.net>
From: "linux-os (Dick Johnson)" <linux-os@analogic.com>
To: "Mika Lawando" <rzryyvzy@trashmail.net>
Cc: <linux-kernel@vger.kernel.org>
Reply-To: "linux-os (Dick Johnson)" <linux-os@analogic.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Thu, 14 Feb 2008, Mika Lawando wrote:

> Jasper Bryant-Greene schrieb:
>> On Thu, 2008-02-14 at 10:30 +0100, rzryyvzy wrote:
>>
>>> /dev/null is often very useful, specially if programs force to save data in some file. But some programs like to creates different temporary file names, so /dev/null could no more work.
>>>
>>> What is with a "/dev/null"-directory?
>>> I mean a "blackhole pseudo directory" which eats every write to null.
>>>
>>> Here is how it could work:
>>> mount -t nulldir nulldir /dev/nulldir
>>>
>>> Now if a program does a create(2),
>>> it creates in the memory the file with its fd.
>>> Then if a program does a write(2) to the fd, it eats the writes and give out fakely it has written the number of bytes.
>>> When the program calls does a close(2) of the fd, then the complete inode is deleted in the memory.
>>>
>>> The directory should  be permanently empty except for the inodes with open file descriptors. So only inode information would be temporary saved in this "nulldir tmpfs" directory.
>>>
>>> Is there already existing a possibility to create a null directory?
>>>
>>
>> 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.
>>
> Unfortunately performance is a concern because if not I would write on
> the hard disk the files, and then remove them with a cronjob.
> But from the point of view of the time of developpment, FUSE is a good
> idea, because its possible to write a filesystem quickly in Perl.
>
> -- 
> Best regards,
> Mika
> --

Creating a null directory wouldn't work because a directory
is just a link to find a file. The actual file gets written
using the file-descriptor, without any reference whosoever
to the path. If you have root privileges, you can use
`mknod tempfile c 1 3` to create a null file with any
name you want. Unfortunately, somebody decided that
you need root privileges to execute mknod so ordinary
users can not do this.


Cheers,
Dick Johnson
Penguin : Linux version 2.6.22.1 on an i686 machine (5588.28 BogoMips).
My book : http://www.AbominableFirebug.com/
_


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