linux-kernel - Re: [RFC][PATCH 2/4] sunrpc: Use utsnamespaces

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Message-Id: <1231284633.14345.152.camel@localhost>
Date:	Tue, 06 Jan 2009 15:30:33 -0800
From:	Matt Helsley <matthltc@...ibm.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Trond Myklebust <trond.myklebust@....uio.no>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	linux-nfs@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Chuck Lever <chuck.lever@...cle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Containers <containers@...ts.osdl.org>,
	Cedric Le Goater <clg@...ibm.com>
Subject: Re: [RFC][PATCH 2/4] sunrpc: Use utsnamespaces

On Tue, 2009-01-06 at 15:58 -0600, Serge E. Hallyn wrote:
> Quoting Trond Myklebust (trond.myklebust@....uio.no):
> > On Tue, 2009-01-06 at 14:02 -0600, Serge E. Hallyn wrote:
> > > Quoting Matt Helsley (matthltc@...ibm.com):
> > > > We can often specify the UTS namespace to use when starting an RPC client.
> > > > However sometimes no UTS namespace is available (specifically during system
> > > > shutdown as the last NFS mount in a container is unmounted) so fall
> > > > back to the initial UTS namespace.
> > > 
> > > So what happens if we take this patch and do nothing else?
> > > 
> > > The only potential problem situation will be rpc requests
> > > made on behalf of a container in which the last task has
> > > exited, right?  So let's say a container did an nfs mount
> > > and then exits, causing an nfs umount request.
> > > 
> > > That umount request will now be sent with the wrong nodename.
> > > Does that actually cause problems, will the server use the
> > > nodename to try and determine the client sending the request?
> > 
> > The NFSv2/v3 umount rpc call will be sent by the 'umount' program from
> > userspace, not the kernel. The problem here is that because lazy mounts
> > exist, the lifetime of the RPC client may be longer than that of the
> 
> Right that was what i was referring to.
> 
> > container. In addition, it may be shared among more than 1 container,
> > because superblocks can be shared.
> 
> Good point.  And in that case what do we care about (even though
> apparently we just might not care at all :) - who did the mount,
> or who is using it?
> 
> In fact one thing I noticed in Matt's patch 3 was that he copied
> in the nodename verbatim, so a future hostname() by the container
> wouldn't be reflected, again not sure if that would matter.

I thought of this. I found the patches that added the nodename in the
RPC client struct and the stale nodename was intentional. That's why I
preserved the copy rather than called utsname() each time.

Cheers,
	-Matt

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