linux-kernel - [PATCH] UTC timestamp option for FAT filesystems

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Message-ID: <486476A5.7040801@skyrush.com>
Date:	Thu, 26 Jun 2008 23:12:05 -0600
From:	Joe Peterson <joe@...rush.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] UTC timestamp option for FAT filesystems

Hi Andrew,

Attached is a patch to provide a new mount option ("tz=UTC") for DOS
(vfat/msdos) filesystems, allowing timestamps to be in coordinated
universal time (UTC) rather than local time in applications where
doing this is advantageous.

In particular, portable devices that use fat/vfat (such as digital
cameras) can benefit from using UTC in their internal clocks, thus
avoiding daylight saving time errors and general time ambiguity issues.
 The user of the device does not have to worry about changing the time
when moving from place or when daylight saving changes.

The new mount option, when set, disables the counter-adjustment that
Linux currently makes to FAT timestamp info in anticipation of the
normal userspace time zone correction.  When used in this new mode, all
daylight saving time and time zone handling is done in userspace as is
normal for many other filesystems (like ext3).  The default mode, which
remains unchanged, is still appropriate when mounting volumes written in
Windows (because of its use of local time).

(I originally based this patch on one submitted last year by Paul
Collins, but I updated it to work with current source and changed
variable/option naming.  Ogawa Hirofumi (who maintains these
filesystems) and I discussed this patch at length on lkml, and he
suggested using the option name in the attached version of the patch.
Barry Bouwsma pointed out a good addition to the patch as well.)

						-Thanks, Joe

View attachment "utc-timestamp-option-for-fat-filesystems.patch" of type "text/x-patch" (7772 bytes)