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

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Message-ID: <aWEWVAqHlTpzsklJ@fedora>
Date: Fri, 9 Jan 2026 15:56:48 +0100
From: Horst Birthelmer <horst@...thelmer.de>
To: Luis Henriques <luis@...lia.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, 
	Amir Goldstein <amir73il@...il.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: Re: [RFC PATCH v2 4/6] fuse: implementation of the
 FUSE_LOOKUP_HANDLE operation

On Fri, Jan 09, 2026 at 02:45:21PM +0000, Luis Henriques wrote:
> On Fri, Jan 09 2026, Miklos Szeredi 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.
> 
> OK, interesting idea.  So, in that case we would have:
> 
> struct fuse_entry_handle_out {
> 	uint64_t nodeid;
> 	uint64_t generation;
> 	uint64_t entry_valid;
> 	struct fuse_file_handle fh;
> }
> 
> I'll then need to have a look at the compound requests closely. (I had
> previously skimmed through the patches that add open+getattr but didn't
> gone too deep into it.)
> 

I am preparing the pull request for libfuse today, so you can have a look at how it will be handled on the libfuse
side. 
That contains a patch to passthrough_hp as well so it supports compounds and you will have something to test, if you want to go that way.

> 
> Cheer,
> -- 
> Luís
>