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SubjectRe: A Layered Kernel: Proposal


On 29 Feb 2004, Christer Weinigel wrote:

> Grigor Gatchev <grigor@zadnik.org> writes:
>
> > > In the linux kernel I think that one of the most important things I've
> > > learned from it: middle layers are usually wrong. Instead of hiding a
> > > device driver behind a middle layer, expose the low level device
> > > driver, but give it a library of common functions to build upon. That
> > > way the driver is in control all the time and can use all the neat
> > > features of the hardware if it wants to, but for all the common tasks
> > > that have to be done, hand them over to the library.
> >
> > By principle, the "least common denominator" type container layers are
> > bad, because of not being extendable; you are completely right here. A
> > class-like driver object model seems better to me. And the class-like
> > model is not the only one that is nicely extendable.
>
> > You seem to be knowledgeable on the topic - what driver object model
> > would you suggest for a driver layer model?
>
> Thanks for the confidence, bur I really don't know, it's much easier
> to criticize someone elses design than to come up with a good one
> myself. :-)

Okay. I will try (hope I'll have the time for all!) to outline the major
driver layer models, with simple lists of advantages and disadvantages,
and to present it as a base for further discussion. (Please keep in mind
that this outline will certainly be not the best ever to exist - maybe a
lot of people around will be able to make it much better. But, anyway,
they will be given the full opportunity to criticize and improve. :-)

> With that said, I think that they way the Linux kernel is moving
> regarding to IDE/SCSI devices is a good idea. Linux has been around
> for a while now and the Linux people have tried lots of things that
> turned out not to be such a good idea after all. Many things are
> still there in the kernel, but if it's important enough, it gets
> cleaned up after a while.

If you mean the abandoning of the SCSI emulation, I couldn't agree more.
Though I haven't digged into the code of this driver group, the move seems
only logical from design viewpoint.


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