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    SubjectRe: Why side-effects on open(2) are evil. (was Re: [RFD w/info-PATCH]device arguments from lookup)
    Date
    On Sunday 27 May 2001 15:32, Edgar Toernig wrote:
    > Daniel Phillips wrote:
    > > It won't, the open for "." is handled in the VFS, not the
    > > filesystem - it will open the directory. (Without needing to be
    > > told it's a directory via O_DIRECTORY.) If you do open("magicdev")
    > > you'll get the device, because that's handled by magicdevfs.
    >
    > You really mean that "magicdev" is a directory and:
    >
    > open("magicdev/.", O_RDONLY);
    > open("magicdev", O_RDONLY);
    >
    > would both succeed but open different objects?

    Yes, and:

    open("magicdev/.", O_RDONLY | O_DIRECTORY);
    open("magicdev", O_RDONLY | O_DIRECTORY);

    will both succeed and open the same object.

    > > I'm not claiming there isn't breakage somewhere,
    >
    > you break UNIX fundamentals. But I'm quite relieved now because I'm
    > pretty sure that something like that will never go into the kernel.

    OK, I'll take that as "I couldn't find a piece of code that breaks, so
    it's on to the legal issues".

    SUS doesn't seem to have a lot to say about this. The nearest thing to
    a ruling I found was "The special filename dot refers to the directory
    specified by its predecessor". Which is not the same thing as:

    open("foo", O_RDONLY) == open ("foo/.", O_RDONLY)

    I don't know about POSIX (I don't have it: a pox on standards
    organizations that don't make their standards freely available) but SUS
    doesn't seem to forbid this.

    --
    Daniel
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