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    SubjectRe: Is there a "blackhole" /dev/null directory?
    Jan Engelhardt wrote:
    > On Feb 14 2008 10:46, Andi Kleen wrote:
    >> Jasper Bryant-Greene <jasper@unix.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@tmr.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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