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

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Message-ID: <87pl7i4sw1.fsf@wotan.olymp>
Date: Fri, 09 Jan 2026 17:07:10 +0000
From: Luis Henriques <luis@...lia.com>
To: Horst Birthelmer <horst@...thelmer.de>
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: [RFC PATCH v2 4/6] fuse: implementation of the
 FUSE_LOOKUP_HANDLE operation

On Fri, Jan 09 2026, Horst Birthelmer wrote:

> 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.

Awesome, thanks for the hint, Horst.  I'll definitely have a look into it.

Cheer,
-- 
Luís