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From: barmar@think.com (Barry Margolin)
Newsgroups: comp.unix.internals
Subject: Re: (was slashes, now NFS devices)
Message-ID: <1991Mar8.074048.13105@Think.COM>
Date: 8 Mar 91 07:40:48 GMT
References: <12662:Mar620:02:2491@kramden.acf.nyu.edu> <1991Mar6.231519.8393@Think.COM> <12713:Mar708:07:3591@kramden.acf.nyu.edu>
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
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In article <12713:Mar708:07:3591@kramden.acf.nyu.edu> brnstnd@kramden.acf.nyu.edu (Dan Bernstein) writes:
>In article <1991Mar6.231519.8393@Think.COM> barmar@think.com (Barry Margolin) writes:
>> Yes, files have state, but NFS *servers* don't have to maintain any state
>> other than the file contents; specifically, there's no per-client or
>> per-process state.
>
>It is irrelevant whether the information is physically kept in the
>server, in the server's filesystem, or in the client. NFS is a protocol
>with state. A filesystem without state is a useless filesystem, because
>by definition it cannot carry any information.

I may be sorry, but I'll try to play your semantic games.

NFS is just a communications protocol, a conduit.  The file system at the
other end of this conduit maintains state, but the conduit itself doesn't.

NFS maintains about as much state as a disk cable.  Yes, there is some
trivial state maintained, such as the identity of the disk, and some
instantaneous state such as the current signals on the wire.  These are so
inconsequential that they can safely be ignored in the context of long-term
state.

The only reason for mentioning statelessness when discussing protocols is
for purposes of comparison of the protocols.  In the context of file access
protocols, it is assumed that the file system itself maintains the state
that is usually associated with file systems.  The issue then becomes
whether the protocol client and server are required to maintain additional
state in order for the remote access mechanism to operate.  NFS servers,
for example, are not required to maintain any additional state; FTP
servers, on the other hand, are required to maintain current directory,
user identity, transmission mode, data connection port, etc.
--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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