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SubjectRe: Is there a "blackhole" /dev/null directory?

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.

Dick Johnson
Penguin : Linux version on an i686 machine (5588.28 BogoMips).
My book :

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