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Date: Mon, 2 Mar 2009 17:27:41 -0500 From: Mike Murphy <mamurph@...clemson.edu> To: Andrew Morton <akpm@...ux-foundation.org> Cc: linux-kernel@...r.kernel.org, linux-input@...r.kernel.org, linux-usb@...r.kernel.org, greg@...ah.com, oliver@...kum.org, fweisbec@...il.com, torvalds@...ux-foundation.org Subject: Re: PATCH [1/3] drivers/input/xpad.c: Improve Xbox 360 wireless support and add sysfs interface On Mon, Mar 2, 2009 at 5:00 PM, Andrew Morton <akpm@...ux-foundation.org> wrote: > > Yup, there's lots of crappy code in the tree, and it is regrettable > that maintainers continue to go ahead and merge that crappy code. > > There's no easy fix for this - you need to be aware of what is right > and what is wrong, but you cannot look at existing code to determine > this :( Part of the problem is that this is the first driver I've really worked on to any extent... and all my formal kernel hacking training was on FreeBSD, not Linux. Given the speed at which kernel development moves, lack of good docs on how best to do development, etc., one simply has to jump into the process and hope for the best. That's awfully hard to do when kernel hacking isn't your full-time occupation.... For example, my dissertation is on virtualization of grid computing systems. I'm doing this driver development simply because I need the driver for my own use... and perhaps one of our affiliated research groups can use it. In my own research, I use Linux exclusively, but all the work I do is at such a high level in userspace that I write all my code in Python. I've taught C programming before and have done a ton of low-level development in a C dialect for sensor networks (nesC for TinyOS), so I'm comfortable with it. Even so, the kernel has its own internal types (hence my unneeded typecasts), and it's not always clear what type belongs where. > > If the code which you're modifying is known (by you) to be wrong then > there are two schools of thought. Some people do like to "match the > existing code". I disagree with that. The code's wrong dammit - we > might as well make the new code "right". If that results in > inconsistent-looking code, well, so be it. We shouldn't have merged > the wrong code in the first place. > > Agreed on the code being correct, but there always arises that question about what constitutes "correct" in any given context (provably dumb things, like dividing by zero, excepted). For example, I broke the xpad driver into two pieces to make it easier to understand. When I go to compile it, the #include "xpad.h" in xpad.c literally causes the preprocessor to dump the contents of xpad.h into xpad.c, before handing the result off to the compiler for conversion to assembly. So the system doesn't really care what goes in which file... that distinction is left to the humans, who have to establish some kind of convention. But where is that convention documented? I could make the argument, for example, that the table of different Xbox devices and their properties should really go in the header file, even though it generates an array. That table constitutes metadata that the driver uses to map device ids to products, so from a software engineering perspective, it is more of a configuration than an executable segment. On the other hand, the only piece that really cares about that data is the driver itself... userspace really only cares about what type of device is actually connected. So from that perspective, it belongs in the C file. But then, whose userspace code is really going to include xpad.h? Circles are fun.... And perhaps this is why we academics tend not to write operating systems that find their way into widespread use... instead ruminating on "nicer" designs (perhaps with a microkernel, *cough*) over more practical solutions :). Mike -- Mike Murphy Ph.D. Candidate and NSF Graduate Research Fellow Clemson University School of Computing 120 McAdams Hall Clemson, SC 29634-0974 USA Tel: +1 864.656.2838 Fax: +1 864.656.0145 http://cirg.cs.clemson.edu/~mamurph -- 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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