From owner-freebsd-fs@FreeBSD.ORG  Thu Nov 10 05:27:19 2011
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Date: Wed, 09 Nov 2011 21:27:16 -0800
From: Kirk McKusick <mckusick@mckusick.com>
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Cc: freebsd-fs@freebsd.org
Subject: Re: write access to various times 
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I am the one that added birthtime and the text that you quote on how 
to set it. I deliberately did not add a new system call to add all 
three (atime, mtime, and birthtime) because programs using the new
system call would not compile/run on any system other than FreeBSD.
Those that followed the admittedly cumbersome double system call 
would compile/run on all systems and those with birthtime would get
it set correctly.

UNIX has never allowed the ctime to be set because backup utilities
such as dump depend on it being correct. A file loaded onto the
system today needs to be dumped at the next backup even if its atime,
mtime, and birthtime all claim that it has been around for years.
If ctime could be set, none of the backup systems would be reliable.

	Kirk McKusick