linux-kernel - Re: [PATCH v2 00/12] make rpc_pipefs be mountable multiple time

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Date:	Fri, 31 Dec 2010 11:54:01 -0500
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Rob Landley <rlandley@...allels.com>
Cc:	"Kirill A. Shutemov" <kas@...nvz.org>,
	Rob Landley <rob@...dley.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Neil Brown <neilb@...e.de>,
	Pavel Emelyanov <xemul@...allels.com>,
	linux-nfs@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/12] make rpc_pipefs be mountable multiple time

On Thu, 2010-12-30 at 04:05 -0600, Rob Landley wrote: 
> On 12/30/2010 03:44 AM, Kirill A. Shutemov wrote:
> >>> If no rpcmount mountoption, no rpc_pipefs was found at
> >>> '/var/lib/nfs/rpc_pipefs' and we are in init's mount namespace, we use
> >>> init_rpc_pipefs.
> >>
> >> It's the "we are in init's mount namespace" that I was wondering about.
> >>
> >> So if I naievely chroot, nfs mount stops working the way it did before I
> >> chrooted unless I do an extra setup step?
> >
> > No. It will work as before since you are still in init's mount namespace.
> > Creating new mount namespace changes rules.
> 
> Ah, CLONE_NEWNS and then you need /var/lib/nfs/rpc_pipefs.  Got it.
> 
> I'm kind of surprised that the kernel cares about a specific path under 
> /var/lib.  (Seems like policy in the kernel somehow.)  Can't it just 
> check the current process's mount list to see if an instance of 
> rpc_pipefs is mounted in the current namespace the way lxc looks for 
> cgroups?  Or are there potential performance/scalability issues with that?

The kernel doesn't give a damn about the /var/lib/nfs/rpc_pipefs bit.
That's all for the benefit of the userland utilities.

  Trond

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com

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