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

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Date:	Thu, 30 Dec 2010 04:05:07 -0600
From:	Rob Landley <rlandley@...allels.com>
To:	"Kirill A. Shutemov" <kas@...nvz.org>
CC:	Rob Landley <rob@...dley.net>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	"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 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?

Rob
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