linux-kernel - Re: [PATCH 00/29] fs: require filesystems to explicitly opt-in to nfsd export support

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Message-Id: <d486fdb8-686c-4426-9fac-49b7dbc28765@app.fastmail.com>
Date: Thu, 15 Jan 2026 13:31:54 -0500
From: "Chuck Lever" <cel@...nel.org>
To: "Amir Goldstein" <amir73il@...il.com>, "Jeff Layton" <jlayton@...nel.org>
Cc: "Christian Brauner" <brauner@...nel.org>,
 "Alexander Viro" <viro@...iv.linux.org.uk>,
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Subject: Re: [PATCH 00/29] fs: require filesystems to explicitly opt-in to nfsd export
 support



On Thu, Jan 15, 2026, at 1:17 PM, Amir Goldstein wrote:
> On Thu, Jan 15, 2026 at 6:48 PM Jeff Layton <jlayton@...nel.org> wrote:
>>
>> In recent years, a number of filesystems that can't present stable
>> filehandles have grown struct export_operations. They've mostly done
>> this for local use-cases (enabling open_by_handle_at() and the like).
>> Unfortunately, having export_operations is generally sufficient to make
>> a filesystem be considered exportable via nfsd, but that requires that
>> the server present stable filehandles.
>
> Where does the term "stable file handles" come from? and what does it mean?
> Why not "persistent handles", which is described in NFS and SMB specs?
>
> Not to mention that EXPORT_OP_PERSISTENT_HANDLES was Acked
> by both Christoph and Christian:
>
> https://lore.kernel.org/linux-fsdevel/20260115-rundgang-leihgabe-12018e93c00c@brauner/
>
> Am I missing anything?

PERSISTENT generally implies that the file handle is saved on
persistent storage. This is not true of tmpfs.

The use of "stable" means that the file handle is stable for
the life of the file. This /is/ true of tmpfs.

-- 
Chuck Lever