Message-ID: <aWimQEokuib7fXjY@infradead.org>
Date: Thu, 15 Jan 2026 00:33:04 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Christian Brauner <brauner@...nel.org>
Cc: Christoph Hellwig <hch@...radead.org>,
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Subject: Re: [PATCH 00/24] vfs: require filesystems to explicitly opt-in to
 lease support

On Thu, Jan 15, 2026 at 09:14:06AM +0100, Christian Brauner wrote:
> On Wed, Jan 14, 2026 at 10:42:48PM -0800, Christoph Hellwig wrote:
> > On Wed, Jan 14, 2026 at 04:20:13PM +0100, Christian Brauner wrote:
> > > > You're still think of it the wrong way.  If we do have file systems
> > > > that break the original exportfs semantics we need to fix that, and
> > > > something like a "stable handles" flag will work well for that.  But
> > > > a totally arbitrary "is exportable" flag is total nonsense.
> > > 
> > > File handles can legitimately be conceptualized independently of
> > > exporting a filesystem. If we wanted to tear those concepts apart
> > > implementation wise we could.
> > > 
> > > It is complete nonsense to expect the kernel to support exporting any
> > > arbitrary internal filesystem or to not support file handles at all.
> > 
> > You are going even further down the path of entirely missing the point
> > (or the two points by now).
> 
> You're arguing for the sake of arguing imho. You're getting exactly what
> we're all saying as evidenced by the last paragraph in your mail: it is
> entirely what this whole thing is about.

I can't even parse what you mean.  And no, I hate these stupid
arguments, and I have much better things to do than dragging this on.

> > If a file systems meets all technical requirements of being nfsd
> > exportable and the users asks for it, it is not our job to make an
> > arbitrary policy decision to say no.
> 
> This is an entirely irrelevant point because we're talking about
> cgroupfs, nsfs, and pidfs. And they don't meet this criteria. cgroupfs
> is a _local resource management filesystem_ why would we ever want to
> support exporting it over the network. It allows to break the local
> delegation model as I've explained. cgroupfs shows _local processes_. So
> a server will see completely nonsensical PID identifiers listed in
> cgroup files and it can fsck around with processes in a remote system.

None of that is a technical argument.  The lack of stable file handles
would be one, and I think we came to the conclusion yesterday that
this is the case.

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