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    SubjectRe: [PATCH] RTC: Add mmap method to rtc character driver
    On Tue, 25 Jul 2006, Neil Horman wrote:

    >>
    >> Quick hacks are frowned upon in the Linux universe. The kernel-user
    >> space interface is supposed to be stable, and thus a hack like this has
    >> to be maintained indefinitely.
    >>
    >> Putting temporary hacks like this in is not a good idea.
    >>
    > Only if you make the mental leap that this is a hack; its not. Its a new
    > feature for a driver. mmap on device drivers is a well known and understood
    > interface. There is nothing hackish about it. And there is no need for it to
    > be temporary either. Why shouldn't the rtc driver be able to export a monotonic
    > counter via the mmap interface? mmtimer does it already, as do many other
    > drivers. Theres nothing unstable about this interface, and it need not be short
    > lived. It can live in perpituity, and applications can choose to use it, or
    > migrate away from it should something else more efficient become available (a
    > gettimeofday vsyscall). More importantly, it can continue to be used in those
    > situations where a vsyscall is not feasable, or simply maps to the nominal slow
    > path kernel trap that one would find to heavy-weight to use in comparison to an
    > mmaped page.

    given that this won't go into 2.6.18 at this point, isn't there time to figure
    out the gettimeofday vsyscall before the 2.6.19 merge window? (in a month or
    so). even if you have to wait until 2.6.20 it's unlikly that any apps could be
    released with an interface to /dev/rtc rather then waiting a little bit for the
    better interface.

    David Lang
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