linux-kernel - Re: [RFC PATCH v2 3/6] fuse: initial infrastructure for FUSE_LOOKUP

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Message-ID: <CAJfpegt-0VDicWso6ZjsFyawuKj8Xf4qwTEth00CdAd-pUNcjQ@mail.gmail.com>
Date: Tue, 16 Dec 2025 12:46:54 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Luis Henriques <luis@...lia.com>
Cc: 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 3/6] fuse: initial infrastructure for
 FUSE_LOOKUP_HANDLE support

On Tue, 16 Dec 2025 at 12:33, Luis Henriques <luis@...lia.com> wrote:
>
> On Tue, Dec 16 2025, Miklos Szeredi wrote:
>
> > On Fri, 12 Dec 2025 at 19:12, Luis Henriques <luis@...lia.com> wrote:
> >>
> >> This patch adds the initial infrastructure to implement the LOOKUP_HANDLE
> >> operation.  It simply defines the new operation and the extra fuse_init_out
> >> field to set the maximum handle size.
> >
> > Since we are introducing a new op, I'd consider switching to
> > fuse_statx for the attributes.
>
> So, just to clarify: you're suggesting that the maximum handle size should
> instead be set using statx.  Which means that the first time the client
> (kernel) needs to use this value it would emit a FUSE_STATX, and cache
> that value for future use.  IIUC, this would also require a new mask
> (STATX_MAX_HANDLE_SZ) to be added.  Did I got it right?

No, using statx as the output of LOOKUP_HANDLE is independent from the
other suggestion.

> What would be the advantages of using statx?  Keeping the unused bytes in
> struct fuse_init_out untouched?

Using fuse_statx instead of fuse_attr would allow btime (and other
attributes added to statx in the future) to be initialized on lookup.

Thanks,
Miklos