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

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Date:	Mon, 02 Jun 2014 21:10:47 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Chuck Lever <chuck.lever@...cle.com>
Cc:	Roger Willcocks <roger@...mlight.ltd.uk>,
	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 Monday 02 June 2014 15:04:27 Chuck Lever wrote:
> On Jun 2, 2014, at 2:58 PM, Roger Willcocks <roger@...mlight.ltd.uk> wrote:
> 
> > 
> > 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.
> 
> You would have to get the IETF’s NFSv4 working group to sign off on
> this change. Otherwise, Linux would be the only NFSv3 implementation
> that supports the extension.
> 
> But I suspect the answer you’d get is “Use NFSv4.”

While I've never dealt with an NFS standardization, I'd assume this is
a workable answer. The NFSv2 and NFSv3 definition clearly defines a valid
range of times until 2106 using unsigned seconds, and that should really
give enough time to migrate to something better (not necessarily NFSv4).

	Arnd
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