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

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Message-ID: <20060913183001.GA1702@moule.localdomain>
Date:	Wed, 13 Sep 2006 20:30:01 +0200
From:	Alexandre Ratchov <alexandre.ratchov@...l.net>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	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, 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.

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.

-- Alexandre
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