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Message-ID: <adamxy79a5u.fsf@roland-alpha.cisco.com> Date: Tue, 16 Mar 2010 15:25:17 -0700 From: Roland Dreier <rdreier@...co.com> To: "Robert P. J. Day" <rpjday@...shcourse.ca> Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: kfifo: possible weird violation of what should be invariant > sure, the code seems to work, but allowing the internal values of a > kfifo to contain invalid values on a regular basis would seem to make > a mess of, say, tracing or debugging. making sure that offset values > actually lie within their valid range would seem to be one of those > ASSERT() things that should always be true, should it not? is there a > reason the design is like this? Actually I believe having the values be free-running without clamping them makes the code much simpler -- the reason being that you preserve the invariant of "in" always being ahead of "out". If you reduce the pointers modulo the size, then you end up having a lot of code that has two cases: one to handle "in > out", and one to handle "in < out because in has wrapped and out hasn't yet". - R. -- Roland Dreier <rolandd@...co.com> For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/index.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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