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Path: utzoo!utgpu!water!watmath!clyde!rutgers!ames!amdahl!dlb!megatest!berryman
From: berryman@megatest.UUCP
Newsgroups: comp.unix.questions
Subject: Re: /dev/null: The final frontier
Message-ID: <1519@megatest.UUCP>
Date: Thu, 21-May-87 18:47:36 EDT
Article-I.D.: megatest.1519
Posted: Thu May 21 18:47:36 1987
Date-Received: Sat, 23-May-87 08:15:55 EDT
References: <100@upas.UUCP>
Distribution: world
Organization: Megatest Corporation, San Jose, Ca
Lines: 45

in article <100@upas.UUCP>, rcw@upas.UUCP (Robert White) says:
> 
> 
> this line == can of raid
> 
> Some of these questions may be trivial. I've lost sleep over them:
> 
> Where do the bytes go when moved or copied to /dev/null?
> Does the machine dissipate the data as heat?
> How does a null device driver work?
> 
> Robert White
> Graphics Information, Inc.
> UUCP: seismo!hao!scicom!qetzal!rcw

Here's the honest to god truth from someone who spent years
optimizing the driver for /dev/null:

1.  The bytes are sorted by age and are kept around for use
by other processes.  Integers are stored in network order
and one must be careful to use ntohs and ntohl before using.

2. The machine stores the data - no heat is released. (see 1).

3. Writes to /dev/null do not occur immediatly but are
buffered in a special buffer cache maintained specifically
for /dev/null.  Writes to /dev/null are processed in order
of decreasing pid*uid/log(averun).  Common program errors
may occur because of this ordering scheme.

Reads from /dev/null are non-blocking and asynchronous so
the programmer may never be sure when the read is completed.

Hope this helps you sleep better.


Ed Blackmond
Lieutenant Kernel Hacker
Megatest Corporation
880 Fox Lane
San Jose, CA 95035
{sun, amd, fortune, dlb}!megatest!eb

Disclaimer -- The above opinions are those of the author and
should be considered the gospel truth.