Messages in this thread | | | Date | Tue, 25 Jul 2006 16:22:31 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] RTC: Add mmap method to rtc character driver |
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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. >
The reason it is a hack is because you're hard-coding the fact that you're taking a global, periodic interrupt. Yes, it can be dealt with scheduler hacks in tickless case, but that seems really heavyweight.
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