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    SubjectRe: Thinking outside the box on file systems
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    On Wed, 15 Aug 2007 13:50:17 PDT, Marc Perkel said:
    > I don't see it as being any worse that what we have
    > now. To open a file you have to start at the bottom
    > and open each directory and evaluate the permissions
    > on the way to the file. In my system you have to look
    > up the permission of the string at each "/" separator.
    > Seems to me that every system would have these same
    > steps.

    No - you need to look at the *whole* string - that's the
    whole *point* of your system, remember?

    Just a few msgs back, you gave a nice example of
    having a file with \ in the name rather than / because
    it came from a Windows user. So you *do* need to check *every*
    pattern against the filename, because it *could* match.
    In a system with several hundred thousand or more patterns,
    that could be painful.

    Also, you need to figure out how to deal with all the various
    silly corner cases that people will end up trying to do.

    Consider the rules:

    peter '*a*' can create
    peter '*b*' cannot create

    Peter tries to create 'foo-ab-bar' - is he allowed to or not?

    For an exersize, either write a program or do by hand:

    Create a list of patterns that correctly express the ownership
    and permissions of *every* file on your current Linux box.

    Then repeat on a large box with multiple users and a few Oracle
    databases or webservers.

    Then write a small tool, that given that list, a username,
    a filename, and the operation (read, write, open, unlink, etc),
    says "Yes or No".

    Then run 'strace /bin/ls' in a large directory, take all the
    filenames listed in the strace output, and see if your tool can
    answer "yes or no" fast enough to make 'ls' feasible.

    Come back when you get that part done, and we'll discuss how it
    would have to work in the kernel.
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