linux-kernel - Re: [RFC] Another take at restarting FUSE servers

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Message-ID: <87ecqary82.fsf@wotan.olymp>
Date: Fri, 07 Nov 2025 09:25:17 +0000
From: Luis Henriques <luis@...lia.com>
To: Stef Bon <stefbon@...il.com>
Cc: "Darrick J. Wong" <djwong@...nel.org>,  Amir Goldstein
 <amir73il@...il.com>,  Bernd Schubert <bschubert@....com>,  Bernd Schubert
 <bernd@...ernd.com>,  "Theodore Ts'o" <tytso@....edu>,  Miklos Szeredi
 <miklos@...redi.hu>,  linux-fsdevel@...r.kernel.org,
  linux-kernel@...r.kernel.org,  Kevin Chen <kchen@....com>
Subject: Re: [RFC] Another take at restarting FUSE servers

Hi Stef,

On Thu, Nov 06 2025, Stef Bon wrote:

> Hi,
>
> is implementing a lookup using a handle to be in the kernel?

What we're talking here is a new FUSE operation, FUSE_LOOKUP_HANDLE.  The
scope here is mostly related to servers restartability: being able to
restart a FUSE server without unmounting the file system.  But other
scopes are also relevant (e.g. NFS exports).

Just in case you missed it, here's a link to the full discussion:

https://lore.kernel.org/all/8734afp0ct.fsf@igalia.com/

and to an older discussion, also relevant:

https://lore.kernel.org/all/CAJfpegvNZ6Z7uhuTdQ6quBaTOYNkAP8W_4yUY4L2JRAEKxEwOQ@mail.gmail.com/

Cheers,
-- 
Luís

> I've written a FUSE fs for sftp using SSH as transport, where the
> lookup call normally has to create a path (relative to the root of the
> sftp) and send that to the remote server.
> It saves the creation of this path if there is a handle available.
> When doing an opendir, this is normally followed by a lookup for every
> dentry. (sftp does not support readdirplus) Now in this case there is
> a handle available (the one used by opendir, or one created with
> open), so the fuse daemon I wrote used that to proceed. (and so not
> create a path).
>
> So it can also go in userspace.
>
> Stef
>