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SubjectRe: [Announce] BKL shifting into drivers and filesystems - beware


On Thu, 13 Jul 2000, Jeff V. Merkey wrote:
> >
>
> Breaking the device drivers, protocol stacks, disk drivers, file
> systems, etc. out of the kernel proper and forcing them to always be
> loadable modules would achieve this end with the added benefit of
> allowing folks to plug in their own optimized binary versions -- Like
> NetWare and NT are today.

No, it would be a complete disaster.

You'd get the same kind of disaster that all binary-only modules have: you
cannot change fundamental interfaces.

In another five or ten years, we may be at the point where the fundamental
interfaces _really_ don't change, and that we've handled all the
scalability issues and that we have no need to add new interfaces. At THAT
point we can just say "ok, drivers are truly independent".

It's not true today.

Basically, the thing that allows 2.4.x to scale as well as it does (and it
does really well: look at the current SpecWeb99 world record numbers, and
compare it to the also-ran second place), is exactly because we had all
the source in one place, and we _could_ make fundamental changes. Claiming
anything else is silly - if we had broken-up device drivers, we'd have
been up shit creek without a paddle. End of story.

This is the thing that people don't understand. In theory it is wonderful
to have modularization. It's the best thing on earth. But if that
modularization means that you can't fix the module interfaces, then you're
going to remain broken for all time.

This is why I rather fix module interfaces early and often. Make sure that
we (a) have good interfaces that matches what the different parts of the
kernel want to have and (b) make people used to the fact that a driver or
a filesystem is not a static thing, and keep them aware of the fact that
it depends on the kernel underneath it.

We're certainly getting closer to a good interface in many areas. The
current VFS interfaces, for example, are pretty good - although many of
the less important ones still depend on the kernel lock etc. But we're
_not_ at the stage yet where we could just say "ok, a driver is a driver,
and we don't need to worry about it".

Linus


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