cvs commit: src/sys/ia64/ia64 sys_machdep.c src/sys/ia64/include sysarch.h

[Marcel Moolenaar]

On Tue, Oct 28, 2003 at 09:09:29AM +0000, Doug Rabson wrote:
> Shouldn't there some kind of access control here? It appears as if
> anyone at all can do inx/outx.

Eventually, yes. There's a possibility that I remove these. The X
server needs to be able to mmap uncachable memory for access to
the hardware. This could also be used to do I/O. The only thing the
kernel needs to export is the base of the memory mapped I/O space
with sysctl in that case.

Note that this affects the VM and PMAP interfaces :-(

> Also, I have a vague feeling that the
> Linux kernel manages to support userland inx/outx without system calls -
> if so, how do they do that?

I think mmap is used for that as well.

> Possibly with modern hardware the cost of the bus transaction dwarfs the
> cost of doing a system call so perhaps it doesn't matter.

The sysarch approach is not optimal. I don't think it's very performance
critical. Modern graphics hardware is memory mapped anyway.

-- 
 Marcel Moolenaar	  USPA: A-39004		 marcel at xcllnt.net