linux-kernel - Re: [PATCH 02/18] xstat: Add a pair of system calls to make extended file stats available [ver #6]

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Message-ID: <19528.64159.999224.437890@samba.org>
Date:	Fri, 23 Jul 2010 12:12:47 +1000
From:	tridge@...ba.org
To:	Ted Ts'o <tytso@....edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jeremy Allison <jra@...ba.org>, linux-cifs@...r.kernel.org,
	linux-nfs@...r.kernel.org, Volker.Lendecke@...net.de,
	samba-technical@...ts.samba.org, linux-kernel@...r.kernel.org,
	Jan Engelhardt <jengelh@...ozas.de>,
	David Howells <dhowells@...hat.com>, viro@...iv.linux.org.uk,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 02/18] xstat: Add a pair of system calls to make
 extended file stats available [ver #6]

Hi Ted,

 > Does it literally mean "file creation time" in terms of when the OS
 > created the file, or does it mean "file" in the sense of
 > application contents.  For example, if an application edits the
 > file and saves it out using "write file to foo.new; sync; rename
 > foo to foo.bak; rename foo.new to foo", should the creation time
 > for the newly written file "foo" be the time when the editor saved
 > out the file (i.e., when "foo.new" was created), or copied from the
 > original file "foo"'s creation time.

In Windows this is can be controlled by applications, but it also is
done at the filesystem level in NTFS using a technique that Microsoft
call "File System Tunneling". If you create a file with the same name
within a short time (default 15s and settable in the registry) of when
the file previously existed then it will get the same CreationTime as
the previous file.

For details see http://support.microsoft.com/kb/172190

Some applications also do this regardless of the registry setting for
MaximumTunnelEntryAgeInSeconds. They use the ability to set the
CreationTime to get the same behaviour.

Cheers, Tridge
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