linux-ext4 - Re: rfc: [patch] change attribute for ext3

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Message-ID: <20061214015212.GA30071@fieldses.org>
Date:	Wed, 13 Dec 2006 20:52:12 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Andreas Dilger <adilger@...sterfs.com>
Cc:	Trond Myklebust <trond.myklebust@....uio.no>,
	Alexandre Ratchov <alexandre.ratchov@...l.net>,
	linux-ext4@...r.kernel.org, nfsv4@...ux-nfs.org
Subject: Re: rfc: [patch] change attribute for ext3

On Wed, Dec 13, 2006 at 06:24:28PM -0700, Andreas Dilger wrote:
> On Sep 13, 2006  14:11 -0400, Trond Myklebust wrote:
> > I would really have preferred a full-blown 64-bit counter as per
> > RFC3530, but I suppose we could always combine this change attribute
> > with the high word from ctime in order to make up the NFSv4 change
> > attribute. That should keep us safe until someone develops a ramdisk
> > with < 1 nsecond access time.
> 
> Trond, can you please elaborate on the need for a 64-bit version counter
> for NFSv4?

I'm not Trond, but....

> What kind of requirements does NFSv4 place on the version?  Monotonic is
> probably a good bet.

The only requirement is that it be unique (assuming a file is never
modified 2^64 times).  Clients can't compare them except for equality.

> Does it need to be global for the filesystem

Nope.

> or is a per-inode version sufficient?

Yes.

> What functionality of NFSv4 needs the version?

Clients use it to revalidate their caches.

--b.
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