Subject: Re: [RFC 11/32] xfs: convert to struct inode_time
From: Roger Willcocks <roger@filmlight.ltd.uk>
To: Dave Chinner <david@fromorbit.com>
Cc: Arnd Bergmann <arnd@arndb.de>, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org, lftan@altera.com, hch@infradead.org,
        john.stultz@linaro.org, "H. Peter Anvin" <hpa@zytor.com>,
        linux-fsdevel@vger.kernel.org, geert@linux-m68k.org,
        tglx@linutronix.de, xfs@oss.sgi.com, joseph@codesourcery.com
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Date: Mon, 02 Jun 2014 12:35:41 +0100
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On Mon, 2014-06-02 at 10:28 +1000, Dave Chinner wrote:

> 
> The 32 bit second counters in timestamps are too small to represent
> time beyond the unix epoch (jan 2038) correctly. Extend the on-disk
> format for a timestamp to include an 8-bit epoch counter so that we
> can extend time for up to 255 Unix epochs. This should be good for
> representing timestamps from 1970 to somewhere around 19,000 A.D....
> 

I assume you're using an 'epoch' variable and not simply using the
padding byte as an eight-bit prefix to the existing 32-bit counter
because the existing counter is signed ?

For long term sanity it might make more sense for the eight-bit value to
be a simple (sign-extended) prefix from 1970.

So if the feature bit is set it's a 40-bit signed time, which is good
for 1970 +/- 17400 years or so.

--
Roger


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