Path: utzoo!attcan!uunet!mcsun!ukc!icdoc!qmw-cs!liam
From: liam@cs.qmw.ac.uk (William Roberts)
Newsgroups: comp.protocols.nfs
Subject: Re: Is RPC in SVR4 implemented in kernel or user level?
Keywords: SVR4
Message-ID: <2503@sequent.cs.qmw.ac.uk>
Date: 12 Jul 90 10:04:52 GMT
References: <1990Jul10.032917.13692@cbnews.att.com> <103795@convex.convex.com>
Organization: Computer Science Dept, QMW, University of London, UK.
Lines: 37

In <103795@convex.convex.com> thurlow@convex.com (Robert Thurlow) writes:

>The kernel has to do RPC over UDP/IP for NFS accesses, so some files
>are needed there.  More files are needed to do RPC for general user
>level applications, and they live in the libraries.  The common files
>in the Sun NFSSRC reference port are identical; our revision control
>system has links in some underlying directories to ensure that the
>changes made are made to both kernel and user level code.

Interesting. Back in NFS 3.0 days there was a significant
difference in that kernel RPC is assumed to be for NFS purposes
and so assumes idempotence, whereas that user-level RPC stuff
doesn't make this assumption.

The actual difference this makes is in the handling of the xid
when a request times out. In the kernel case (idempotent) the
xid for the retransmission is the same as the original request
and so a delayed reply to the original message would be
acceptable. In the user level case (non idempotent) the xid is
incremented so a delayed reply to the original request will
actually be rejected.

The non-idempotence assumption is why the dreadful slowness of
the mountd daemon actually causes severe problems (see annual
discussions on this group). I have been saying for years that
SunRPC should allow you to specify which behaviour you want,
but nobody ever seems to take any notice.

Back to Rob's message: if you have identcial source, do you
still have this distinction in the behaviour and if so, how do
you achieve it?
-- 

William Roberts                 ARPA: liam@cs.qmw.ac.uk
Queen Mary & Westfield College  UUCP: liam@qmw-cs.UUCP
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