From: Neil Brown <neilb@suse.de>
Subject: Re: 2.4 vs 2.6
Date: Tue, 13 Jun 2006 13:29:42 +1000
Message-ID: <17550.12582.742528.454837@cse.unsw.edu.au>
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Cc: mehta kiran <kiranmehta1981@yahoo.com>,
	Vijay Chauhan <kernel.vijay@gmail.com>, nfs@lists.sourceforge.net,
	Greg Banks <gnb@sgi.com>
To: "J. Bruce Fields" <bfields@fieldses.org>
In-Reply-To: message from J. Bruce Fields on Monday May 29
Sender: nfs-bounces@lists.sourceforge.net
Errors-To: nfs-bounces@lists.sourceforge.net

On Monday May 29, bfields@fieldses.org wrote:
> On Tue, May 30, 2006 at 11:12:08AM +1000, Greg Banks wrote:
> > On Mon, May 29, 2006 at 12:02:36PM -0400, J. Bruce Fields wrote:
> > > I don't see why this *has* to be done on demand, though, unless the
> > > export table is extremely large and only sparsely used.  I might be
> > > missing something.
> > 
> > /mnt/data *.domain1.company.com(ro,sync) *.domain2.company.com(rw,sync)
> 
> I realize that the ip->client-name mapping is too large to preload into
> the kernel.
> 
> It's the (path, client-name) --> export options that I wonder about.

Having the mapping permanently in the kernel rather than filled in on
demand would mean that:

 - the filesystem has to be mounted the whole time, and we cannot do
   any on-demand mounting (based on fsid) - not that we currently do.
   This is a fairly small point however.
 - the client-names would need to be known in advance.  It seems
   obvious that they would be, but they aren't.
   What do you do if you get a request from an IP address that matches
   several of the tags in /etc/exports ? e.g.
      /export1 @somehosts(rw,root_squash)
      /export2 @otherhosts(ro,no_root_squash)

   If a request arrives from a host which is in both 'somehosts' and
   'otherhosts', then what name do you give to the kernel for that IP
   address?
   We currently say the IP address maps to 
          @somehosts+@otherhosts
   (or something like that) and then tell the kernel any of the
   following as required:
          /export1 @somehosts+@otherhosts  -> rw,root_squash
          /export1 @somehosts  -> rw,root_squash
          /export2 @somehosts+@otherhosts  -> ro,no_root_squash
          /export2 @otherhosts  -> ro,no_root_squash
          
Hopefully you can see that giving a full (path, client-name ) ->
export mapping the kernel in advance is not practical.

NeilBrown


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