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From: hedrick@topaz.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: Errors that can't happen !
Message-ID: <10679@topaz.RUTGERS.EDU>
Date: Thu, 2-Apr-87 19:36:23 EST
Article-I.D.: topaz.10679
Posted: Thu Apr  2 19:36:23 1987
Date-Received: Sat, 4-Apr-87 16:51:23 EST
References: <535@ssl-macc.co.uk>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 20

A user reported a error
	rfs_read: attempt to read from non-file

from his Sun.  I saw that once when somebody tried to open a directory
over NFS and read it like a file, instead of using readdir.  Note that
I am talking kernel level.  User programs can read directories, but
the way this has to be implemented is that the kernel notices the
file being opend is a directory, issues readdir calls to the other
machine, and then gives the user program the data formatted so as
to look like a raw directory file.  This may seem arcane, but it's
the only way to handle a network where different machines have
different directory formats, but where applications insist on
reading the directories directly.  In Sun 3.0, the NFS server would
still let another machine's NFS read the directory as a file.
Presumably this would still be meaningful if both machines had the
same directory structure.  however it appears (based on experiment --
I didn't look at the code) that in 3.2, Sun's NFS server rejected
this with the error message quoted above, or something very close to
it.  I suppose it could also be that somebody tried to open a device
or socket over NFS.