From: "J. Bruce Fields" <bfields@fieldses.org>
Subject: Re: 2.4 vs 2.6
Date: Fri, 26 May 2006 15:31:18 -0400
Message-ID: <20060526193118.GB17761@fieldses.org>
References: <17526.44653.228663.713864@cse.unsw.edu.au> <20060526081905.73641.qmail@web51609.mail.yahoo.com>
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Cc: Neil Brown <neilb@suse.de>, nfs@lists.sourceforge.net,
	Vijay Chauhan <kernel.vijay@gmail.com>
To: mehta kiran <kiranmehta1981@yahoo.com>
In-Reply-To: <20060526081905.73641.qmail@web51609.mail.yahoo.com>
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On Fri, May 26, 2006 at 01:19:05AM -0700, mehta kiran wrote:
> Hi,
> 
> 1. I noticed that 2.6 kernel is not aware of 
>    exportfs until client tries to mount. It only
>    after this that proc nfsd filesystem shows this
>    in list of exports due to upcall.
>    Was 2.4 kernel aware of exportfs when the
>    filesystem was first exported or mounted ?
> 
> 2. Can you let me know advantage 2.6 export approach
>    over 2.4 export approach ? 
>    Is this approach required due to 
>    security/authentication integration with NFS(say 
>    ip->name conversion for security ) ?

The kernel has to know whether an incoming IP address matches, say,
"*.umich.edu."  But we don't want to add an entire DNS client
implementation to the kernel.  And we also can't preload the kernel with
every possible IP address that might match *.umich.edu.  So we allow
the kernel to ask mountd for that information when it needs it.

This isn't actually necessary for an NFSv2/v3 server, because mountd
always gets a "mount" request from any client before the kernel gets any
NFS requests from that client, so mountd can tell the kernel about the
new client then.

But NFSv4 clients don't contact mountd first.  Neither do v2/v3 clients
that are failing over from another server.  So you need the upcalls to
handle those cases.

That justifies the auth_unix_ip upcall, anyway; I'm less sure about the
others.

--b.


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