linux-ext4 - Re: [PATCH 02/18] xstat: Add a pair of system calls to make extended file stats available [ver #6]

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Message-ID: <20100730183819.GE21729@fieldses.org>
Date:	Fri, 30 Jul 2010 14:38:19 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Neil Brown <neilb@...e.de>
Cc:	David Howells <dhowells@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Jeremy Allison <jra@...ba.org>, Volker.Lendecke@...net.de,
	linux-cifs@...r.kernel.org, linux-nfs@...r.kernel.org,
	samba-technical@...ts.samba.org, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 02/18] xstat: Add a pair of system calls to make
 extended file stats available [ver #6]

On Thu, Jul 29, 2010 at 09:04:01AM +1000, Neil Brown wrote:
> On Wed, 28 Jul 2010 18:28:02 +0100
> David Howells <dhowells@...hat.com> wrote:
> 
> > Neil Brown <neilb@...e.de> wrote:
> > 
> > > ctime and mtime have real cache-coherence semantics which require them being
> > > updated by the kernel (whether the cache is on an NFS client, in a backup
> > > archive, or in a .o translation of a .c file).
> > 
> > So does creation time, at least for CIFS caching.  Creation time has potential
> > for spotting when the object at a pathname has changed for something else,
> > given the lack of inode number and inode generation from windows servers.
> > Creation time gives us one more datum to use.
> 
> This justifies for me why a CIFS client would want to extract the
> creation-time from the CIFS protocol, but not why you want to expose it via a
> generic interface.
> The kernel/filesystem doesn't need to maintain creation-time to meet this
> need, only the CIFS server needs to maintain it

For what it's worth, the NFSv4 server would also export creation time if
we had it.

--b.
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