On Thu, Dec 30, 2010 at 04:05:07AM -0600, Rob Landley wrote:

On 12/30/2010 03:44 AM, Kirill A. Shutemov wrote:

quoted

quoted

quoted

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.)

Yep. It's bad, but there is way to overwrite the default.

Other way is to leave 'rpcmount' mountoption without default.
get_rpc_pipefs(NULL) in init's mount namespace will always return
init_rpc_pipefs, without filesystem lookup.
get_rpc_pipefs(NULL) in non-init's mount namespace will always return
error.

So you will have to specify 'rpcmount' mountoption for every nfs mount in
container. Hmm, I guess, it may confuse user.

Or we can try to move the default to userspace. /sbin/mount.nfs?

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?

What should we do if we have several rpc_pipefs mounts in the namespace?

-- 
 Kirill A. Shutemov
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