linux-kernel - Re: [PATCH v3 00/16] make rpc_pipefs be mountable multiple time

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Date:	Thu, 20 Jan 2011 10:52:39 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Rob Landley <rlandley@...allels.com>
Cc:	"Kirill A. Shutemov" <kas@...nvz.org>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Neil Brown <neilb@...e.de>,
	Pavel Emelyanov <xemul@...allels.com>,
	linux-nfs@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Al Viro <viro@...IV.linux.org.uk>,
	containers@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/16] make rpc_pipefs be mountable multiple time

On Thu, Jan 20, 2011 at 07:57:52AM -0600, Rob Landley wrote:
> I've also mounted NFS shares in test environments I never mounted
> rpc_pipefs in.  (It's possible that the nfs.mount command was doing so
> for me, and apparently unmounting it again afterwards.)  My test
> environment is exporting with the userspace NFS daemon so it's not using
> the kernel cacheing infrastructure.

If you grep for rpc_mkpipe() you'll see it's only used in the idmapping
and rpcsec_gss code; which means you wouldn't need it unless using NFSv4
(which uses idmapping) or rpcsec_gss.

> > There is client dir (nfs/clntX) in rpc_pipefs for every sunrpc client.
> > Both client and server (see fs/nfsd/nfs4callback.c) can create sunrpc
> > client. So we rpc_pipefs on both side.
> 
> Ok, both client and server can create instances.  And use them to do what?
> 
> I understand that the kernel needs to handle RPC calls to service NFS
> requests, what I'm not figuring out is how userspace is involved after
> the initial mount except on the other side of filesystem-agnostic system
> calls.

If you want to see the code on the userland side of the interfaces, see
utils/gssd and utils/idmapd in the nfs-utils code.

--b.
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