Re: [PATCH RFC] fuse: check if system-wide io_uring is enabled

[Jens Axboe <axboe@kernel.dk>]

On 10/21/25 2:31 PM, Bernd Schubert wrote:
> Add check_system_io_uring() to determine if system-wide io_uring is
> available for a FUSE mount. This is useful because FUSE io_uring
> can only be enabled if the system allows it. Main issue with
> fuse-io-uring is that the mount point hangs until queues are
> initialized. If system wide io-uring is disabled queues cannot
> be initialized and the mount will hang till forcefully umounted.
> Libfuse solves that by setting up the ring before replying
> to FUSE_INIT, but we also have to consider other implementations
> and might get easily missed in development.
> 
> When mount specifies user_id and group_id (e.g., via unprivileged
> fusermount with s-bit) not equal 0, the permission check must use
> the daemon's credentials, not the mount task's (root) credentials.
> Otherwise io_uring_allowed() incorrectly allows io_uring due to
> root's CAP_SYS_ADMIN capability.

Rather than need various heuristics, it'd be a lot better if asking for
fuse-io_uring would just not "hang" at mount time and be able to recover
better?

There are also other considerations that may mean that part of init will
fail, doesn't seem like the best idea to me to attempt to catch all of
this rather than just be able to gracefully handle errors at
initialization time.

-- 
Jens Axboe