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    SubjectRe: Is there a "blackhole" /dev/null directory?
    Am Thu, 14 Feb 2008 16:00:06 +0100 (CET)
    schrieb Jan Engelhardt <>:

    > 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.
    > 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.

    Well, the problem seems to be that a "directory" is not just data but
    also contains metadata. While it's easy to write data to /dev/null, you
    cannot simply discard metadata associated with a directory. So, such a
    "/dev/null-directory" would have to remember metadata (at least all
    created filenames including subdirectories) in the same way as other
    filesystems do. Only file _content_ can be discarded.
    To be honest, I still cannot see many sensible usecases for that...


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