Re: patent on O_ATOMICLOOKUP [Re: [PATCH] loopable tmpfs (2.4.17)]

Linus Torvalds
2002-05-25T18:45:37Z

On Sat, 25 May 2002, Karim Yaghmour wrote:
>
> Blinders ehh... Well, if you would care to ask I would answer.
>
> In reality, what you point out is actually a non-issue since the hard-rt
> user-land tasks are not allowed to call on normal Linux services. They
> can only call on RTAI services which are exported by an extra soft-int.
> These services are hard-rt, so there's no problem there.

.. which was exactly what I said:

"..every single spinlock in the kernel assumes that the kernel isn't
preempted, which means that user apps that can preempt the kernel
cannot use them."

Karim, I don't _need_ to download RTAI or ask you questions about how it
works, because this is fundamental "RT-101" stuff. This is what priority
inversion is all about: if you make user land more important than the
kernel, it _cannot_ stay RT and use kernel services.

I went on to say:

"Karim claims to give "user land" hard-real-time abilities, but the
fact is, it's not "user land" any more. it's a limited shadow, and a
_perversion_ of what user land is supposed to be all about."

Which certainly should have told you that I understood the limitations of
RTAI very well indeed. And I reject them.

Linus