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    SubjectRe: [PATCH 1/1] LinuxPPS: Pulse per Second support for Linux
    Rodolfo Giometti wrote:
    >
    > Please read the following consideratios before sending to /dev/null!
    > :)
    >
    > RFC considerations
    > ------------------
    >
    > While implementing a PPS API as RFC 2783 defines and using an embedded
    > CPU GPIO-Pin as physical link to the signal, I encountered a deeper
    > problem:
    >
    > At startup it needs a file descriptor as argument for the function
    > time_pps_create().
    >
    > This implies that the source has a /dev/... entry. This assumption is
    > ok for the serial and parallel port, where you can do something
    > usefull beside(!) the gathering of timestamps as it is the central
    > task for a PPS-API. But this assumption does not work for a single
    > purpose GPIO line. In this case even basic file-related functionality
    > (like read() and write()) makes no sense at all and should not be a
    > precondition for the use of a PPS-API.
    >

    It's not a precondition for a file descriptor, either. There are plenty
    of ioctl-only device drivers in existence.

    Furthermore, a file descriptor doesn't imply a device entry. Consider
    pipe(2), for example.

    As far as the kernel is concerned, a file handle is a nice, uniform
    system for providing communication between the kernel and user space.
    It doesn't matter if one can read() or write() on it; it's perfectly
    normal to support only a subset of the normal operations.

    -hpa
    -
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