Weekly edition	Kernel	Security	Distributions	Contact Us	Search
Archives	Calendar	Subscribe	Write for LWN	LWN.net FAQ	Sponsors

LCA: Andrew Tanenbaum on creating reliable systems

Posted Jan 18, 2007 22:42 UTC (Thu) by nix (subscriber, #2304)
In reply to: LCA: Andrew Tanenbaum on creating reliable systems by jamesh
Parent article: LCA: Andrew Tanenbaum on creating reliable systems

So Minix I/O port access always involves at least two ring transitions
*per port I/O*?

Given the timing-sensitive nature of much port I/O that strikes me as both
wildly impractical and somewhat dangerous.

(Log in to post comments)

Posted Jan 24, 2007 14:01 UTC (Wed) by kleptog (subscriber, #1183) [Link]

On i386 hardware, it's possible to grant an unprivelidged processes access to particular I/O ports, without having to do any ring transitions. On Linux it's the ioperm() function call.

These days people use memory-mapped I/O so mmap() is what you mostly need.

LCA: Andrew Tanenbaum on creating reliable systems

Posted Feb 2, 2007 13:46 UTC (Fri) by willy (subscriber, #9762) [Link]

Yes, but minix explicitly doesn't do ioperm, it really does call down to the microkernel to do IO port accesses. He talked about how 'evil' mmaped IO was.