Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!bu-cs!cloud9!banyan!gil
From: gil@banyan.UUCP (Gil Pilz@Eng@Banyan)
Newsgroups: comp.unix.wizards
Subject: Re: What SHOULD go in the kernel
Message-ID: <569@banyan.UUCP>
Date: 30 Oct 89 21:47:15 GMT
References: <2186@ektools.UUCP> <47040@bbn.COM> <17166@rpp386.cactus.org> <3718@altos86.Altos.COM>
Reply-To: gil@banyan.com
Distribution: na
Organization: Banyan Systems, Inc.
Lines: 21

In article <3718@altos86.Altos.COM> dtynan@altos86.Altos.COM (Dermot Tynan) writes:
>Another reason for not paging the kernel, is instruction restart within a
>device driver.  A classic example is a UART with a FIFO.  Allowing
>instruction restart after a page-fault, when the driver is reading from the
>UART, and writing to (pageable) memory will create havoc.  Intel products
>are insulated from this, because they have a separate I/O bus, which means
>that I/O can only be done to an on-chip register.  However, memory-mapped
>I/O will fail horribly.

So page in (if necessary) and lock down the target page(s) *before*
starting the I/O, then unlock them on I/O completion.  What's the
problem ?

"forty orange cookies, some are black some are white
 what would it take to make 'em all turn *just* *right* ?
 forty orange cookies sitting on the bed
 one took off, the others followed
 went straight for my head"
	- house of large sizes

Gilbert W. Pilz Jr.       gil@banyan.com