linux-kernel - Re: [PATCH v3 0/3] fuse: Expose more information of fuse backing files to userspace

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Message-ID: <CAOQ4uxjDwk6NA_UKiJuXfyY=2G33rruu3jr70pthFpBBbSgp1A@mail.gmail.com>
Date: Fri, 9 May 2025 09:36:10 +0200
From: Amir Goldstein <amir73il@...il.com>
To: chenlinxuan@...ontech.com
Cc: Miklos Szeredi <miklos@...redi.hu>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Bernd Schubert <bernd.schubert@...tmail.fm>
Subject: Re: [PATCH v3 0/3] fuse: Expose more information of fuse backing
 files to userspace

On Fri, May 9, 2025 at 8:34 AM Chen Linxuan via B4 Relay
<devnull+chenlinxuan.uniontech.com@...nel.org> wrote:
>
> Please review this patch series carefully. I am new to kernel
> development and I am not quite sure if I have followed the best
> practices, especially in terms of seq_file, error handling and locking.
> I would appreciate any feedback.
>
> I have do some simply testing using libfuse example [1]. It seems to
> work well.
>
> [1]: https://github.com/libfuse/libfuse/blob/master/example/passthrough_hp.cc
>
> Signed-off-by: Chen Linxuan <chenlinxuan@...ontech.com>
> ---

Very nice work Chen!

Please give reviewers some more time to review before posting v4
and you do not have to post v4 on account of my minor comments
unless Miklos requests it.

One thing that now comes to mind is how lsof is going to use and present
this information?

I did not look at how lsof presents io_uring fixed files, but I assume that
an io_uring is always associated with a specific user process.
How does lsof display the io_uring files?

I guess with io_uring, lsof can list a pid which admin can kill to release the
open files?
This is not the case with displaying conn, because lsof is not designed
to list fuse conn.

Is there a way for userspace to get from conn to fuse server pid?

Even if there were a way, I think that the fuse connection and open
backing files can certainly outlive the killed fuse server process.

But still, in the common case, if lsof can blame the fuse server process,
in most cases, killing the fuse server process will release the backing files,
so it may be worth looking into this.

Thanks,
Amir.