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

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Message-ID: <0427cbb9-f3f2-40e6-a03a-204c1798921d@ddn.com>
Date: Tue, 16 Dec 2025 08:54:26 +0000
From: Bernd Schubert <bschubert@....com>
To: Joanne Koong <joannelkoong@...il.com>, Luis Henriques <luis@...lia.com>
CC: Miklos Szeredi <miklos@...redi.hu>, Amir Goldstein <amir73il@...il.com>,
	"Darrick J. Wong" <djwong@...nel.org>, Kevin Chen <kchen@....com>, Horst
 Birthelmer <hbirthelmer@....com>, "linux-fsdevel@...r.kernel.org"
	<linux-fsdevel@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Matt Harvey <mharvey@...ptrading.com>,
	"kernel-dev@...lia.com" <kernel-dev@...lia.com>
Subject: Re: [RFC PATCH v2 4/6] fuse: implementation of the FUSE_LOOKUP_HANDLE
 operation

On 12/16/25 09:49, Joanne Koong wrote:
> 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.

It would be quite a waste if one only needs something like 12 or 16
bytes, wouldn't it? 128 is the upper limit, but most file systems won't
need that much.


Thanks,
Bernd