Re: silent semantic changes with reiser4

Linus Torvalds
2004-09-02T22:58:37Z

On Thu, 2 Sep 2004, Tom Vier wrote:
>
> > Not user space. They may be "ring 3" from a CPU standpoint, but they
> > aren't user space from a _user_ standpoint - it's still very much a
> > separate address space, with domain protection.
>
> How are they different from regular user procs, other then being trusted to
> manage certain resources?

Ehh, they are separate the same way "inetd" is separate. It's not a _user_
proc, it's a system proc. The user can't actually do anything about it.

In many ways UNIX _is_ a microkernel. It does nonessential stuff in "user
space". Anything that is critical for performance or the working of the
machine is in kernel space.

The big difference between UNIX and what people _call_ "microkernels" is
that UNIX has a very functional and sane partitioning of what is a
critical thing.

But from a kernel _protection_ angle, the only part that is important is
that the services be in some protected domain. That was what started this
discussion: 99% of what the kernel does is protecting shared data. Whether
it does so by passing it on to some trusted third party or not is an
implementation issue, and is totally pointless from a user standpoint,
since the user won't see it anyway.

Linus