linux-kernel - Re: [PATCH v3 2/3] fs: fuse: add backing

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Message-ID: <CAJfpegvhZ8Pts5EJDU0efcdHRZk39mcHxmVCNGvKXTZBG63k6g@mail.gmail.com>
Date: Fri, 9 May 2025 16:00:27 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: chenlinxuan@...ontech.com
Cc: Amir Goldstein <amir73il@...il.com>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] fs: fuse: add backing_files control file

On Fri, 9 May 2025 at 08:34, Chen Linxuan via B4 Relay
<devnull+chenlinxuan.uniontech.com@...nel.org> wrote:
>
> From: Chen Linxuan <chenlinxuan@...ontech.com>
>
> Add a new FUSE control file "/sys/fs/fuse/connections/*/backing_files"
> that exposes the paths of all backing files currently being used in
> FUSE mount points. This is particularly valuable for tracking and
> debugging files used in FUSE passthrough mode.

This is good work, thanks.

My concern is that this is a very fuse specific interface, even though
the problem is more generic: list hidden open files belonging to a
kernel object, but not installed in any fd:

 - SCM_RIGHTS
 - io_uring
 - fuse

So we could have a new syscall or set of syscalls for this purpose.
But that again goes against my "this is not generic enough" pet peeve.

So we had this idea of reusing getxattr and listxattr (or implementing
a new set of syscalls with the same signature) to allow retrieving a
hierarchical set of attributes belonging to a kernel object.  This one
would also fit that pattern, so...

Thoughts?

Thanks,
Miklos