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: <20241206160358.GC7820@frogsfrogsfrogs>
Date: Fri, 6 Dec 2024 08:03:58 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Amir Goldstein <amir73il@...il.com>
Cc: Christoph Hellwig <hch@...radead.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>
Subject: Re: [PATCH 0/4] exportfs: add flag to allow marking export
 operations as only supporting file handles

On Thu, Dec 05, 2024 at 12:57:28PM +0100, Amir Goldstein wrote:
> On Thu, Dec 5, 2024 at 1:38 AM Christoph Hellwig <hch@...radead.org> wrote:
> >
> > On Sun, Dec 01, 2024 at 02:12:24PM +0100, Christian Brauner wrote:
> > > Hey,
> > >
> > > Some filesystems like kernfs and pidfs support file handles as a
> > > convenience to enable the use of name_to_handle_at(2) and
> > > open_by_handle_at(2) but don't want to and cannot be reliably exported.
> > > Add a flag that allows them to mark their export operations accordingly
> > > and make NFS check for its presence.
> > >
> > > @Amir, I'll reorder the patches such that this series comes prior to the
> > > pidfs file handle series. Doing it that way will mean that there's never
> > > a state where pidfs supports file handles while also being exportable.
> > > It's probably not a big deal but it's definitely cleaner. It also means
> > > the last patch in this series to mark pidfs as non-exportable can be
> > > dropped. Instead pidfs export operations will be marked as
> > > non-exportable in the patch that they are added in.
> >
> > Can you please invert the polarity?  Marking something as not supporting
> > is always awkward.  Clearly marking it as supporting something (and
> > writing down in detail what is required for that) is much better, even
> > it might cause a little more churn initially.
> >
> 
> Churn would be a bit annoying, but I guess it makes sense.
> I agree with Christian that it should be done as cleanup to allow for
> easier backport.
> 
> Please suggest a name for this opt-in flag.
> EXPORT_OP_NFS_EXPORT???

That's probably too specific to NFS--

AFAICT the goal here is to prevent exporting {pid,kern}fs file handles
to other nodes, correct?  Because we don't want to allow a process on
another computer to mess around with processes on the local computer?

How about:

/* file handles can be used by a process on another node */
#define EXPORT_OP_ALLOW_REMOTE_NODES	(...)

--D

> Thanks,
> Amir.
>