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From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.unix.wizards
Subject: Re: NFS performance
Keywords: i am ignorant
Message-ID: <3695@auspex.auspex.com>
Date: 20 Jul 90 21:06:47 GMT
References: <7887@lynx.UUCP> <3688@auspex.auspex.com>
Distribution: na
Organization: Auspex Systems, Santa Clara
Lines: 13

>    (1) In SunOS 4.0 (and higher), cat doesn't actually do reads in
>        the case where the output goes to /dev/null.

Just in case anybody was about to interpret this as meaning that "cat"
special-cases "/dev/null":

For those not aware of how this happens, "cat" in 4.0 "mmap()"s the
file(s) being concatenated, if it can, and just writes from the
mapped-in areas (mapped 1MB at a time, as I remember).  This means that
the handler for the object being written to, in effect, does all the
reading, by faulting in the data from the file; since the handler for
"/dev/null" never looks at the data being written, it's never faulted
in.