Re: [PATCH v3 5/6] fuse: {io-uring} Allow reduced number of ring queues

[Luis Henriques <luis@igalia.com>]

On Mon, Oct 13 2025, Bernd Schubert wrote:

> Queues selection (fuse_uring_get_queue) can handle reduced number
> queues - using io-uring is possible now even with a single
> queue and entry.
>
> Signed-off-by: Bernd Schubert <bschubert@ddn.com>
> ---
>  fs/fuse/dev_uring.c       | 35 +++--------------------------------
>  fs/fuse/inode.c           |  2 +-
>  include/uapi/linux/fuse.h |  3 +++
>  3 files changed, 7 insertions(+), 33 deletions(-)
>
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> index 92401adecf813b1c4570d925718be772c8f02975..aca71ce5632efd1d80e3ac0ad4e81ac1536dbc47 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -999,31 +999,6 @@ static int fuse_uring_commit_fetch(struct io_uring_cmd *cmd, int issue_flags,
>  	return 0;
>  }
>  
> -static bool is_ring_ready(struct fuse_ring *ring, int current_qid)
> -{
> -	int qid;
> -	struct fuse_ring_queue *queue;
> -	bool ready = true;
> -
> -	for (qid = 0; qid < ring->max_nr_queues && ready; qid++) {
> -		if (current_qid == qid)
> -			continue;
> -
> -		queue = ring->queues[qid];
> -		if (!queue) {
> -			ready = false;
> -			break;
> -		}
> -
> -		spin_lock(&queue->lock);
> -		if (list_empty(&queue->ent_avail_queue))
> -			ready = false;
> -		spin_unlock(&queue->lock);
> -	}
> -
> -	return ready;
> -}
> -
>  /*
>   * fuse_uring_req_fetch command handling
>   */
> @@ -1051,13 +1026,9 @@ static void fuse_uring_do_register(struct fuse_ring_ent *ent,
>  	cpumask_set_cpu(queue->qid, ring->numa_registered_q_mask[node]);
>  
>  	if (!ring->ready) {
> -		bool ready = is_ring_ready(ring, queue->qid);
> -
> -		if (ready) {
> -			WRITE_ONCE(fiq->ops, &fuse_io_uring_ops);
> -			WRITE_ONCE(ring->ready, true);
> -			wake_up_all(&fc->blocked_waitq);
> -		}
> +		WRITE_ONCE(fiq->ops, &fuse_io_uring_ops);
> +		WRITE_ONCE(ring->ready, true);
> +		wake_up_all(&fc->blocked_waitq);
>  	}
>  }
>  
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index d1babf56f25470fcc08fe400467b3450e8b7464a..3f97cc307b4d77e12334180731589c579b2eb7a2 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1503,7 +1503,7 @@ static struct fuse_init_args *fuse_new_init(struct fuse_mount *fm)
>  		FUSE_SECURITY_CTX | FUSE_CREATE_SUPP_GROUP |
>  		FUSE_HAS_EXPIRE_ONLY | FUSE_DIRECT_IO_ALLOW_MMAP |
>  		FUSE_NO_EXPORT_SUPPORT | FUSE_HAS_RESEND | FUSE_ALLOW_IDMAP |
> -		FUSE_REQUEST_TIMEOUT;
> +		FUSE_REQUEST_TIMEOUT | FUSE_URING_REDUCED_Q;
>  #ifdef CONFIG_FUSE_DAX
>  	if (fm->fc->dax)
>  		flags |= FUSE_MAP_ALIGNMENT;
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index c13e1f9a2f12bd39f535188cb5466688eba42263..3da20d9bba1cb6336734511d21da9f64cea0e720 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -448,6 +448,8 @@ struct fuse_file_lock {
>   * FUSE_OVER_IO_URING: Indicate that client supports io-uring
>   * FUSE_REQUEST_TIMEOUT: kernel supports timing out requests.
>   *			 init_out.request_timeout contains the timeout (in secs)
> + * FUSE_URING_REDUCED_Q: Client (kernel) supports less queues - Server is free
> + *			 to register between 1 and nr-core io-uring queues
>   */
>  #define FUSE_ASYNC_READ		(1 << 0)
>  #define FUSE_POSIX_LOCKS	(1 << 1)
> @@ -495,6 +497,7 @@ struct fuse_file_lock {
>  #define FUSE_ALLOW_IDMAP	(1ULL << 40)
>  #define FUSE_OVER_IO_URING	(1ULL << 41)
>  #define FUSE_REQUEST_TIMEOUT	(1ULL << 42)
> +#define FUSE_URING_REDUCED_Q (1ULL << 43)

This flag doesn't seem to be used anywhere.  Should it be removed, or will
there be any usage for it?

Cheers,
-- 
Luís


>  /**
>   * CUSE INIT request/reply flags
>
> -- 
> 2.43.0
>