Date: Wed, 15 Dec 2010 17:29:28 -0500
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Simon Kirby <sim@hostway.ca>, linux-nfs@vger.kernel.org
Subject: Re: System CPU increasing on idle 2.6.36
Message-ID: <20101215222928.GE9646@fieldses.org>
References: <20101215180813.GA7773@fieldses.org>
 <1292437333.3068.14.camel@heimdal.trondhjem.org>
 <20101215183816.GB7773@fieldses.org>
 <1292441630.3068.55.camel@heimdal.trondhjem.org>
 <20101215194956.GA9646@fieldses.org>
 <1292443028.3068.60.camel@heimdal.trondhjem.org>
 <20101215201908.GB9646@fieldses.org>
 <1292445128.3068.71.camel@heimdal.trondhjem.org>
 <20101215214854.GC9646@fieldses.org>
 <1292451346.3068.93.camel@heimdal.trondhjem.org>
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On Wed, Dec 15, 2010 at 05:15:46PM -0500, Trond Myklebust wrote:
> On Wed, 2010-12-15 at 16:48 -0500, J. Bruce Fields wrote:
> > On Wed, Dec 15, 2010 at 03:32:08PM -0500, Trond Myklebust wrote:
> > > On Wed, 2010-12-15 at 15:19 -0500, J. Bruce Fields wrote:
> > > 
> > > > Could you give an example of a case in which all of the following are
> > > > true?:
> > > > 	- the administrator explicitly requests numeric id's (for
> > > > 	  example by setting nfs4_disable_idmapping).
> > > > 	- numeric id's work as long as the client uses auth_sys.
> > > > 	- they no longer work if that same client switches to krb5.
> > > 
> > > Trivially:
> > > 
> > > Server /etc/passwd maps trondmy to uid 1000
> > > Client /etc/passwd maps trondmy to uid 500
> > 
> > I understand that any problematic case would involve different
> > name<->id mappings on the two sides.
> > 
> > What I don't understand--and apologies if I'm being dense!--is what
> > sequence of operations exactly would work in this situation if we
> > automatically switch idmapping based on auth flavor, and would not work
> > without it.
> > 
> > Are you imagining a future client that is also able to switch auth
> > flavors on the fly (say, based on whether a krb5 ticket exists or not),
> > or just unmounting and remounting to change the security flavor?
> > 
> > Are you thinking of creating a file under one flavor and accessing it
> > under another?
> 
> Neither.
> 
> I'm quite happy to accept that my user may map to completely different
> identities on the server as I switch authentication schemes. Fixing that
> is indeed the administrator's problem.
> 
> I'm thinking of the simple case of creating a file, and then expecting
> to see that file appear labelled with the correct user id when I do 'ls
> -l'. That should work irrespectively of the authentication scheme that I
> choose.
> 
> In other words, if I authenticate as 'trond' on my client or to the
> kerberos server, then do
> 
>         touch foo
>         ls -l foo
> 
> I should see a file that is owned by 'trond'.

Thanks, understood; but then, this isn't about behavior that occurs when
a user *changes* authentication flavors.

It's about what happens when someone sets nfs4_disable_idmapping but
shouldn't have.

Is that an important case to care about?

--b.