linux-kernel - Re: [RFC PATCH v2 4/6] fuse: implementation of the FUSE_LOOKUP

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Message-ID: <CAOQ4uxjXN0BNZaFmgs3U7g5jPmBOVV4HenJYgdfO_-6oV94ACw@mail.gmail.com>
Date: Fri, 9 Jan 2026 16:03:14 +0100
From: Amir Goldstein <amir73il@...il.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: Luis Henriques <luis@...lia.com>, "Darrick J. Wong" <djwong@...nel.org>, 
	Bernd Schubert <bschubert@....com>, Kevin Chen <kchen@....com>, 
	Horst Birthelmer <hbirthelmer@....com>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Matt Harvey <mharvey@...ptrading.com>, 
	kernel-dev@...lia.com
Subject: Re: [RFC PATCH v2 4/6] fuse: implementation of the FUSE_LOOKUP_HANDLE operation

On Fri, Jan 9, 2026 at 1:38 PM Miklos Szeredi <miklos@...redi.hu> wrote:
>
> On Fri, 9 Jan 2026 at 12:57, Luis Henriques <luis@...lia.com> wrote:
>
> > I've been trying to wrap my head around all the suggested changes, and
> > experimenting with a few options.  Since there are some major things that
> > need to be modified, I'd like to confirm that I got them right:
> >
> > 1. In the old FUSE_LOOKUP, the args->in_args[0] will continue to use the
> >    struct fuse_entry_out, which won't be changed and will continue to have
> >    a static size.
>
> Yes.
>
> > 2. FUSE_LOOKUP_HANDLE will add a new out_arg, which will be dynamically
> >    allocated (using your suggestion: 'args->out_var_alloc').  This will be
> >    a new struct fuse_entry_handle_out, similar to fuse_entry_out, but
> >    replacing the struct fuse_attr by a struct fuse_statx, and adding the
> >    file handle struct.
>
> Another idea: let's simplify the interface by removing the attributes
> from the lookup reply entirely.  To get back the previous
> functionality, compound requests can be used: LOOKUP_HANDLE + STATX.

What about FUSE_CREATE? FUSE_TMPFILE?
and more importantly READDIRPLUS dirents?

How do you envision the protocol extension for those if fuse_entry_handle
does not contain fuse_statx?

Thanks,
Amir.

>
> > 3. FUSE_LOOKUP_HANDLE will use the args->in_args[0] as an extension header
>
> No, extensions go after the regular request data: headers, payload,
> extension(s).
>
> We could think about changing that for uring, where it would make
> sense to put the extensions after the regular headers, but currently
> it doesn't work that way and goes into the payload section.
>
> In any case LOOKUP_HANDLE should follow the existing practice.
>
> >    (FUSE_EXT_HANDLE).  Note that other operations (e.g. those in function
> >    create_new_entry()) will actually need to *add* an extra extension
> >    header, as extension headers are already being used there.
>
> Right.
>
> >    This extension header will use the new struct fuse_entry_handle_out.
>
> Why _out?
>
> It should just be a struct fuse_ext_header followed by a struct
> fuse_file_handle.
>
> Thanks,
> Miklos