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

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Message-ID: <20110120113552.GB24349@shutemov.name>
Date:	Thu, 20 Jan 2011 13:35:52 +0200
From:	"Kirill A. Shutemov" <kas@...nvz.org>
To:	Rob Landley <rlandley@...allels.com>
Cc:	"Kirill A. Shutemov" <kas@...nvz.org>,
	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>,
	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 Mon, Jan 17, 2011 at 06:30:16AM -0600, Rob Landley wrote:
> On 01/14/2011 07:48 AM, Kirill A. Shutemov wrote:
> > Prepare nfs/sunrpc stack to use multiple instances of rpc_pipefs.
> > Only for client for now.
> 
> Ok, Google is being really unhelpful here.

It's better if you read the code. :)
> 
> What is rpc_pipefs for?  What uses it, and to do what exactly?  Is it
> used by nfs server code, or by the client code, or both?  Is it a way
> for userspace to talk to the kernel, or for the kernel to talk to
> itself?  Is it used at mount time, or during filesystem operation?

Ok, It try to answer. Please correct me, if I'm wrong.

rpc_pipefs is a userland/kernel interface (I don't see kernel-kernel
usecases, but it's possible, I guess).
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.
rpc_pipefs uses not only on mount time. See old idmapper, for example.

> I'm interested in giving this patch series a much more thorough review,
> but I can't figure out what the subsystem it's modifying actually _is_.
> 
> (Maybe this is something to do with filesystems/nfs/rpc-cache.txt?)
> 
> Rob

-- 
 Kirill A. Shutemov
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