Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!haven!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.wizards
Subject: Re: kernel questions
Message-ID: <15948@mimsy.UUCP>
Date: 14 Feb 89 23:53:28 GMT
References: <885@ncr-sd.SanDiego.NCR.COM>
Distribution: usa
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 21

In article <885@ncr-sd.SanDiego.NCR.COM> kit@falstaf.SanDiego.NCR.COM
(Kit Chow) writes:
>1) If a user process can be 'nailed' into memory, is there still a
>need to copyin(k) data from user virtual address space into kernel
>address space? If no, could the kernel then access the user data
>in the user virtual address space with minimum overhead?

A) no, and b) yes, and in fact this is what `raw I/O' does.  The
details are quite machine-dependent, however.  For instance, some
hardware requires that all I/O addresses be physically contiguous,
which will probably be false in a demand-paging system.  Other
hardware can only talk to a specific (limited) address space.

>2) What exactly does wakeup(k) do to move processes from the
>SLEEP state to the READY state?

Mark it runnable and put it into the run queue.  This is another
place that things are likely to vary between different kernels.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris