Re: RT patch acceptance

Esben Nielsen
2005-06-01T15:19:41Z

On Wed, 1 Jun 2005, Andrea Arcangeli wrote:

> On Wed, Jun 01, 2005 at 04:45:57PM +0200, Esben Nielsen wrote:
> > the implementation of the former spinlock, now a mutex, is using a
> > raw_spin_lock, which disables interrupts.
>
> It's not _raw_spin_lock that disables irq. It's spin_lock_irq that does
> that and it has been redefinined into an operation that doesn't disable
> irq.
>
> The patent text goes like this "providing a software emulator to disable
> and enable interrupts from the general purpose operating system;
>
> marking interrupts as "soft disabled" and not "soft enabled" in response
> to requests from the general purpose operating system to disable
> interrupts; ".
>

PREEMPT_RT doesn't do that. If you from Linux request to disable irqs or
preemption you just do it. Nothing in PREEMPT_RT prevents you. There is no
"software emulation" involved at all. Redefining spin_lock() to mean
lock_mutex() is clearly not the same as putting in a sub-kernel and
redifiing cli()/sti() in Linux, which is what the patent covers.

> I'm not a lawyer and I hope to be wrong, but I sure wouldn't bet the
> farm on it. You should ask a lawyer to make sure that non-GPL code is
> not infringing IMHO. This assuming that this could be a problem. It was
> a problem for RTAI users, people is used to the fact userland doesn't
> need to be GPL. Note that LGPL and BSD code will infringe too (i.e. no
> glibc etc..).

Neither am I. But I know if I start to interpret patens that way I would
have to stop writing software right now as every line of code would be
covered by some patent if you start to look at it your way.

Esben