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

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Message-ID: <CAJnrk1aN4icSpL4XhVKAzySyVY+90xPG4cGfg7khQh-wXV+VaA@mail.gmail.com>
Date: Tue, 16 Dec 2025 16:49:37 +0800
From: Joanne Koong <joannelkoong@...il.com>
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: [RFC PATCH v2 4/6] fuse: implementation of the FUSE_LOOKUP_HANDLE operation

On Sat, Dec 13, 2025 at 2:14 AM Luis Henriques <luis@...lia.com> wrote:
>
> The implementation of LOOKUP_HANDLE modifies the LOOKUP operation to include
> an extra inarg: the file handle for the parent directory (if it is
> available).  Also, because fuse_entry_out now has a extra variable size
> struct (the actual handle), it also sets the out_argvar flag to true.
>
> Most of the other modifications in this patch are a fallout from these
> changes: because fuse_entry_out has been modified to include a variable size
> struct, every operation that receives such a parameter have to take this
> into account:
>
>   CREATE, LINK, LOOKUP, MKDIR, MKNOD, READDIRPLUS, SYMLINK, TMPFILE
>
> Signed-off-by: Luis Henriques <luis@...lia.com>
> ---
>  fs/fuse/dev.c             | 16 +++++++
>  fs/fuse/dir.c             | 87 ++++++++++++++++++++++++++++++---------
>  fs/fuse/fuse_i.h          | 34 +++++++++++++--
>  fs/fuse/inode.c           | 69 +++++++++++++++++++++++++++----
>  fs/fuse/readdir.c         | 10 ++---
>  include/uapi/linux/fuse.h |  8 ++++
>  6 files changed, 189 insertions(+), 35 deletions(-)
>

Could you explain why the file handle size needs to be dynamically set
by the server instead of just from the kernel-side stipulating that
the file handle size is FUSE_HANDLE_SZ (eg 128 bytes)? It seems to me
like that would simplify a lot of the code logic here.

Thanks,
Joanne