Messages in this thread | | | Date | Mon, 25 Jun 2001 02:06:12 +0200 | From | Anders Larsen <> | Subject | Re: Is it useful to support user level drivers |
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"Richard B. Johnson" wrote: > > On Fri, 22 Jun 2001, Anders Larsen wrote: > > > "Richard B. Johnson" wrote: > > > > > > QNX does not have any difference between user-space and kernel space. > > > It's not paged-virtual. It's just one big sheet of address space > > > with no memory protection (everything is shared). All procedures > > > to be executed are known at compile time. > > > > That's completely, utterly untrue. > > QNX does indeed sport paged-virtual memory with memory protection; > > (although QNX4 does not support swap). > > Then QNX is not the QNX that I have used.
Or you haven't used it recently (= within the past 10 years)
> > User-mode interrupts are standard procedure; the deadlock problems > > Alan has mentioned do not apply, since any running process is > > always resident in memory. > > Shared regions have to be explicitly created; access is *not* open > > to anybody. > > > > Nothing has to be known at "compile time"; QNX is a full-featured > > OS with dynamic loading. > > > > The QNX that I have used, advertised as QNX, and been around since > 32-bit ix86 was available, is EXACTLY as I stated.
Dynamic loading of executables has been in QNX for as long as I know it (fifteen years). With the appearance of QNX version 4 some ten years ago came 32-bit address space, full memory management/protection etc.
> > > Therefore, any piece of code can do anything it wants including > > > handling hardware directly. > > > > Again not true; only privileged processes can enter kernel mode > > to execute port I/O instructions directly. > > The QNX that I have used, again is EXACTLY as stated.
It must have been an early QNX version 2, then. QNX 2 did not have any memory protection.
> If you have used a different QNX, then QNX has either changed > radically, or is a different company/QNX than what I used. > And, I had a lot of good experiences with it since standard > I/O was provided, as was boot, but it was an open book otherwise > in which you were not prevented from doing anything you wanted > to do, at any instant you wanted to do it.
Of course QNX has changes radically over the decades (it's been around for some twenty years now); what I frowned at was that you made your statements as if they would apply to the *current* state of affairs, which they certainly do not.
cheers Anders -- "In theory there is no difference between theory and practice. In practice there is." - Yogi Berra - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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