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Re: Is there no way to shared code with Linux and other OSes?

To: Chad Reese <>
Subject: Re: Is there no way to shared code with Linux and other OSes?
From: "Kevin D. Kissell" <>
Date: Sat, 22 Nov 2008 03:54:40 -0600
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[This should be good for some useless weekend flaming.]

Chad Reese wrote:
Watching the discussion about Octeon patches submitted by Cavium
Networks, it seems apparent the majority of the problems simply come
from the fact that the code was written to be shared between multiple
operating systems. Code for programming the low level details of
hardware doesn't really change if the OS is Linux, VxWorks, BSD, or
something else. I've found it very depressing that most of the comments
basically come down to "this doesn't match the kernel coding standard,
change it". Obviously rewriting code for every coding standard and OS is
just a bug farm. Fixes will never get merged into all the rewrites.
If one had a fixed list of OSes that one wanted to support, each of which had a stable set of coding standards, then in principle it might be possible to derive some lowest-common-denominator coding standards from the intersection of sets. As you point out, the resulting constraints (no typedefs for Linux, no identifiers more than N characters for other environments, etc.) may directly with efficient coding and maintenance. That's a trade-off you get to make versus maintaining multiple variants.
Cavium can't be the first to want to share code. We'd like Octeon to be
well supported in the Linux kernel, but we'd also like other OSes to
work well too. There has to be some sort of middle ground here. Our base
"library" that is completely OS agnostic is actually license under the
BSD license to allow maximum portability between various OSes. What have
other people done before?

Through the discussion on the Octeon patches a number of bugs have been
uncovered and code has been improved. This part of the kernel submit
process is truly great. It just bothers me that so much needs to be
rewritten for arbitrary reasons.
A consistent coding style is, I think you'll agree, an aid to coding and maintenence in large-scale programming, and while the Linux kernel isn't really all that big as software systems go, it's big enough to warrant a consistent style. What's disconcerting is the "feature creep" in the coding standard. Typedefs weren't banned by Linux in the beginning, and there are legacy typedefs in the system for exactly the reasons why software engineers working in C have used them for generations. At some point, if Linux isn't going to become the Latin liturgy of operating systems, the standard will need to move away from such arbitrary dogmatism. The argument given for banning typedefs altogether is that nested typedefs are confusing to programmers. I strongly suspect that there's a coding rule that would exclude the kinds of abuses that provoked the rule while allowing sensible use of typedefs for portability and future-proofing. But that's not going to happen any time real soon.
For example, there has been lots of complaints that we use typedefs
throughout our code. Some people may not like them, but they have been
useful in the past. Some code used to use structures to reference chip
registers. Later due to new features, we found it necessary to change
the struct to a union with anonymous members. Because of the typedefs we
were able to change the fields for the new features without breaking
compatibility with existing code. If we'd used "struct" everywhere
instead of a typedef, all existing code would have to change for no
other reason except to substitute "union" for "struct". Not everyone has
 the freedom of the kernel programmers to ignore code outside of the
I had a similar experience of annoyance with Linux dogma years ago, so I very much sympathize with your reaction. However, isn't there a less elegant but functional alternative, such as passing pointers to void around and casting to type as appropriate, that you could have used had you known in advance that the Linux priesthood would reject typedefs as heresy?


         Kevin K.

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