linux-kernel - Re: [PATCH] Fuse: Add backing file support for uring

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Message-ID: <9eb067b6-bde8-4505-a9f9-33f33c323b6d@gmail.com>
Date: Sat, 22 Feb 2025 16:13:43 -0600
From: Moinak Bhattacharyya <moinakb001@...il.com>
To: Amir Goldstein <amir73il@...il.com>
Cc: Bernd Schubert <bernd@...ernd.com>, Miklos Szeredi <miklos@...redi.hu>,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 io-uring@...r.kernel.org
Subject: Re: [PATCH] Fuse: Add backing file support for uring_cmd

> So fc->backing_files_map are not really fds registered for IO,
> they are essential references to backing inodes.

That's essentially what registered FD's are, they fget() the FD and 
stash them in an internal data structure. It's not necessarily for I/O 
per se, its more a mechanism to ensure fast Uring access to a given FD.

 > Could you explain how fd registration into the ring would help here?

 From my understanding of the previous problem with passthrough, we want 
to make sure that one can't issue arbitrary write() calls to the open 
FUSE FD to sneak in an arbitrary file passthrough (I admit, I don't 
fully understand the concern). In any case, this is obviated by using 
URING-only mechanisms, right?