linux-kernel - Re: [PATCH 0/4] exportfs: add flag to allow marking export operations as only supporting file handles

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Message-ID: <Z1b0ZQAstSIf-ZMo@infradead.org>
Date: Mon, 9 Dec 2024 05:45:09 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Amir Goldstein <amir73il@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	"Darrick J. Wong" <djwong@...nel.org>,
	Christian Brauner <brauner@...nel.org>,
	Jeff Layton <jlayton@...nel.org>,
	Erin Shepherd <erin.shepherd@....eu>,
	Chuck Lever <chuck.lever@...cle.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	stable <stable@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Shaohua Li <shli@...com>
Subject: Re: [PATCH 0/4] exportfs: add flag to allow marking export
 operations as only supporting file handles

On Mon, Dec 09, 2024 at 10:16:36AM +0100, Greg KH wrote:
> > Maybe we were wrong about the assumption that cgroupfs should be treated
> > specially and deny export cgroups over nfs??
> 
> Please don't export any of the "fake" kernel filesystems (configfs,
> cgroups, sysfs, debugfs, proc, etc) over nfs please.  That way lies
> madness and makes no sense.

Umm, yes: it sounds like a pretty useless idea.  But you can do that
today with a userland nfs server, so why explicitly forbid it for
the kernel nfs server.  In either case you absolutely have to want it,
you're not going to accidentally NFS export a file system.

I'm still trying to understand what problem we're trying to solve here.