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    SubjectRe: I/O completion ports for Linux
    Theodore Y. Ts'o wrote:
    > This is not to say that completion ports are not without their problems.
    > There are also questions of what happens if you try to register more
    > than one asyncronous I/O --- does it return an error, overwrite the
    > previous I/O request, etc? Do you allow asyncronous reads and writes?
    > Since I'm on the road, I still haven't had a chance to look at Robey's
    > proposal, but there are some design/API questions that we need to
    > consider.

    My current implementation keeps a queue of operations per
    completion-port. So it's possible to have multiple outstanding I/O
    requests on one fd -- but they're served in the order that you made the
    requests. I believe NT only allows one oustanding async I/O request per
    fd, which strongly indicates that they store this info in their
    equivalent of "struct file". I'm not sure how much of a limitation this
    is in practice... ? It would simplify the implementation a lot, but I'm
    not sure if it's a good thing overall. It seems like there are probably
    some pretty good reasons that you might want to have two or more
    outstanding async I/O requests on a single fd.

    Robey Pointer | "So that's what an invisible barrier | looks like." -Time Bandits | (join the 90's retro bandwagon early!)

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