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

Trond Myklebust
2010-12-31T16:54:24Z

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@netapp.com