*BSD News Article 90431


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From: cjs@cynic.portal.ca (Curt Sampson)
Newsgroups: comp.os.linux.misc,comp.os.linux.networking,comp.os.linux.setup,comp.unix.bsd.bsdi.misc,comp.unix.bsd.misc
Subject: Re: User-space file systems.  (Re: Linux vs BSD)
Date: 5 Mar 1997 12:12:20 -0800
Organization: Internet Portal Services, Inc.
Lines: 37
Message-ID: <5fkk34$182@cynic.portal.ca>
References: <5e6qd5$ivq@cynic.portal.ca> <5fj9q4$s0i@pulp.ucs.ualberta.ca> <5fjek4$gtm@cynic.portal.ca> <5fk1t1$3mq@web.nmti.com>
NNTP-Posting-Host: cynic.portal.ca
Xref: euryale.cc.adfa.oz.au comp.os.linux.misc:162990 comp.os.linux.networking:70980 comp.os.linux.setup:101140 comp.unix.bsd.bsdi.misc:6222 comp.unix.bsd.misc:2728

In article <5fk1t1$3mq@web.nmti.com>, Peter da Silva <peter@nmti.com> wrote:

>But, Curt, reading a *local* disk block makes two kernel transitions anyway.

I don't understand this. Reading a local disk block is done in the
kernel. If the NFS server daemon is in the kernel, the request to
read comes from the kernel, the read is done in the kernel, and
the data is sent back by the kernel. Where does userland get involved
at all?

>Yes, moving NFS into the kernel is a Good Thing, but it's not obvious to
>me that it's enough of a Good Thing to make it such a big issue.

It depends on whether your NFS server is a Pentium Pro or a Sun 3. :-)
Obviously, when you've got a Pentium system on a 10 Mbps network,
it's no big deal. But you remember as well as I do what processors
were like five years ago.

I'm perhaps a little more neutral on this issue that I make myself
out to be, though. While I certainly wouldn't re-write the BSD NFS
server to run as a userland daemon, I would seriously consider
writing one for userland rather than kernel if I were starting from
scratch.

>The most common tool that was implemented there of all the things
>a microkernel could do that a monolithic kernel can't, was new kinds of file
>systems. If you can do userland file systems you get 95% of what people want
>microkernels for anyway.

Ah, but now we're not talking about NFS servers, we're talking
about clients, which are a different kettle of fish.

cjs
-- 
Curt Sampson    cjs@portal.ca	   Info at http://www.portal.ca/
Internet Portal Services, Inc.	   Through infinite myst, software reverberates
Vancouver, BC  (604) 257-9400	   In code possess'd of invisible folly.