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

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Message-Id: <1158174362.6072.27.camel@lade.trondhjem.org>
Date:	Wed, 13 Sep 2006 15:06:02 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Alexandre Ratchov <alexandre.ratchov@...l.net>
Cc:	linux-ext4@...r.kernel.org, nfsv4@...ux-nfs.org
Subject: Re: rfc: [patch] change attribute for ext3

On Wed, 2006-09-13 at 20:30 +0200, Alexandre Ratchov wrote:
> On Wed, Sep 13, 2006 at 02:11:11PM -0400, Trond Myklebust wrote:
> > On Wed, 2006-09-13 at 18:42 +0200, Alexandre Ratchov wrote:
> > > hello, 
> > > 
> > > here is a small patch that adds the "change attribute" for ext3
> > > file-systems;
> > > 
> > > the change attribute is a simple counter that is reset to zero on
> > > inode creation and that is incremented every time the inode data is
> > > modified (similarly to the "ctime" time-stamp).
> > 
> > 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.
> > 
> 
> do you mean something like "(ctime.tv_sec << 32) | change_attribute"? this
> would allow 2^32 inode changes per second.

Yes. As I said, that probably ought to suffice for now.

> For ext3 it's hard to find unused bits in the on-disk inode structure, but
> ext4 inode may become larger in the future, allowing a 64bit counter.

In anticipation of that event, could you please change the field in
'struct stat' and 'struct stat64' to be an 'unsigned long long' instead
of the current 'unsigned long'?

All the other fields are internal to the kernel, so a future change of
their size should not matter.

Cheers,
  Trond

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