linux-kernel - Re: [RFC 11/32] xfs: convert to struct inode

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Message-Id: <1401735504.6065.227.camel@montana.filmlight.ltd.uk>
Date:	Mon, 02 Jun 2014 19:58:24 +0100
From:	Roger Willcocks <roger@...mlight.ltd.uk>
To:	Chuck Lever <chuck.lever@...cle.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	linux-arch@...r.kernel.org,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	LKML Kernel <linux-kernel@...r.kernel.org>, lftan@...era.com,
	Christoph Hellwig <hch@...radead.org>, john.stultz@...aro.org,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	geert@...ux-m68k.org, tglx@...utronix.de, xfs@....sgi.com,
	joseph@...esourcery.com
Subject: Re: [RFC 11/32] xfs: convert to struct inode_time

On Mon, 2014-06-02 at 11:04 -0400, Chuck Lever wrote:

> NFSv2/3 timestamps are a pair of unsigned 32-bit values: one value for
> seconds since midnight GMT Jan 1, 1970, and one value for nanoseconds.
> (See the definition of nfstime3 in RFC 1813).
> 

nfstime3 could be extended by redefining the otherwise unused
nanoseconds bits{31,30} as seconds{33,32}, to give a (signed) 34-bit
seconds field and an unsigned 30-bit nanoseconds field.

This could represent 1970 +/- 272 years.

Servers could indicate they can understand the extended time format by
adding a new FSINFO capability - FSF3_CANSETTIME_EX.

Clients would use a new SET_TO_CLIENT_TIME_EX time_how enum when sending
timestamps so old servers would be protected from new clients.

Old clients don't need to be protected from new servers because the
on-the-wire bit pattern for dates between 1970 and 2106 stays the same,
so they're no worse off than they were before.

Arguably the new server ought to clamp out-of-range timestamps before
sending them to old clients but that would need per-client state (and
nfs3 is stateless.)

--
Roger

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