Re: poll() in 2.6 and beyond

From: David Dillow (dave_at_thedillows.org)
Date: 03/03/04

  • Next message: Andrew Morton: "Re: per-cpu blk_plug_list" 
    To: root@chaos.analogic.com
Date:	02 Mar 2004 22:57:01 -0500

    On Tue, 2004-03-02 at 18:32, Richard B. Johnson wrote:
    > Yes. The code I attached earlier shows that the poll() in a driver
    > gets called (correctly), then it calls poll_wait(). Unfortunately
    > the call to poll_wait() returns immediately so that the return
    > value from the driver's poll() is whatever it was before some
    > event occurred that the driver was going to signal with
    > wake_up_interruptible().

    You've been handed a clue enough times now that you should understand
    that poll_wait() does not, and has never, put the process to sleep.

    If you can show a case where do_poll() returns stale data, then by all
    means do so. We will be happy to fix any such error in the kernel.

    You say do_poll() looses the status returned from your driver's poll
    method. If your driver is truly returning a nonzero status from the
    poll() method call, then a simple read of the code in do_pollfd() will
    show that the only way it looses information from that event mask is if
    your user space is not setting that event type in pollfd.events.

    If I were you, I'd check two things:
    1) that your poll method is really returning a non-zero status when you
    think it is
    2) that your user space program is really asking for all events you
    think it is

    I think you'll find your problem is not this well-used mechanism in the
    kernel.

    Dave
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  • Next message: Andrew Morton: "Re: per-cpu blk_plug_list"

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