Re: [PATCH v6 2/6] fuse: add FUSE_IO_URING_CMD_ADD_QUEUE

On 7/16/26 19:59, Joanne Koong wrote:
> fuse-over-io-uring queues are currently created lazily, as a side effect
> of the first FUSE_IO_URING_CMD_REGISTER command for a given qid. This
> ties queue creation to entry registration.
> 
> Add a FUSE_IO_URING_CMD_ADD_QUEUE command so a server can create a queue
> explicitly, decoupling queue setup from entry registration. This is
> additionally a prerequisite for FUSE_IO_URING_CMD_ADD_BUFPOOL, which
> attaches a buffer pool to an existing queue and therefore needs the
> queue to have been created first.
> 
> Signed-off-by: Joanne Koong <[email protected]>
> ---
>  fs/fuse/dev_uring.c       | 45 +++++++++++++++++++++++++++++++++------
>  include/uapi/linux/fuse.h |  8 ++++++-
>  2 files changed, 45 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> index b7c6100c4176..fdf1058e582c 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -281,7 +281,8 @@ void fuse_uring_conn_init(struct fuse_chan *fch)
>  }
>  
>  static struct fuse_ring_queue *fuse_uring_create_queue(struct fuse_ring *ring,
> -						       int qid)
> +						       int qid,
> +						       bool fail_if_exists)
>  {
>  	struct fuse_chan *fch = ring->chan;
>  	struct fuse_ring_queue *queue;
> @@ -289,11 +290,11 @@ static struct fuse_ring_queue *fuse_uring_create_queue(struct fuse_ring *ring,
>  
>  	queue = kzalloc_obj(*queue, GFP_KERNEL_ACCOUNT);
>  	if (!queue)
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  	pq = fuse_pqueue_alloc();
>  	if (!pq) {
>  		kfree(queue);
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  	}
>  
>  	queue->qid = qid;
> @@ -316,7 +317,7 @@ static struct fuse_ring_queue *fuse_uring_create_queue(struct fuse_ring *ring,
>  		spin_unlock(&fch->lock);
>  		kfree(queue->fpq.processing);
>  		kfree(queue);
> -		return ring->queues[qid];
> +		return fail_if_exists ? ERR_PTR(-EEXIST) : ring->queues[qid];
>  	}
>  
>  	/*
> @@ -1189,9 +1190,9 @@ static int fuse_uring_register(struct io_uring_cmd *cmd,
>  
>  	queue = READ_ONCE(ring->queues[qid]);
>  	if (!queue) {
> -		queue = fuse_uring_create_queue(ring, qid);
> -		if (!queue)
> -			return -ENOMEM;
> +		queue = fuse_uring_create_queue(ring, qid, false);
> +		if (IS_ERR(queue))
> +			return PTR_ERR(queue);
>  	}
>  
>  	/*
> @@ -1206,6 +1207,30 @@ static int fuse_uring_register(struct io_uring_cmd *cmd,
>  	return fuse_uring_do_register(ent, cmd, issue_flags);
>  }
>  
> +static int fuse_uring_add_queue(struct io_uring_cmd *cmd, struct fuse_chan *fch)
> +{
> +	const struct fuse_uring_cmd_req *cmd_req =
> +		io_uring_sqe128_cmd(cmd->sqe, struct fuse_uring_cmd_req);
> +	struct fuse_ring *ring = smp_load_acquire(&fch->ring);
> +	unsigned int qid = READ_ONCE(cmd_req->qid);
> +	uint64_t flags = READ_ONCE(cmd_req->flags);
> +	struct fuse_ring_queue *queue;
> +
> +	if (!ring || flags)
> +		return -EINVAL;
> +
> +	if (qid >= ring->nr_queues) {
> +		pr_info_ratelimited("fuse: Invalid ring qid %u\n", qid);
> +		return -EINVAL;
> +	}
> +
> +	queue = fuse_uring_create_queue(ring, qid, true);
> +	if (IS_ERR(queue))
> +		return PTR_ERR(queue);
> +
> +	return 0;
> +}
> +
>  /*
>   * Entry function from io_uring to handle the given passthrough command
>   * (op code IORING_OP_URING_CMD)
> @@ -1272,6 +1297,12 @@ int fuse_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
>  			return err;
>  		}
>  		break;
> +	case FUSE_IO_URING_CMD_ADD_QUEUE:
> +		err = fuse_uring_add_queue(cmd, fch);
> +		if (err)
> +			pr_info_once("FUSE_IO_URING_CMD_ADD_QUEUE failed err=%d\n",
> +				     err);
> +		return err;
>  	default:
>  		return -EINVAL;
>  	}
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index c13e1f9a2f12..cfb055c0c764 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -240,6 +240,9 @@
>   *  - add FUSE_COPY_FILE_RANGE_64
>   *  - add struct fuse_copy_file_range_out
>   *  - add FUSE_NOTIFY_PRUNE
> + *
> + *  7.46
> + *  - add FUSE_IO_URING_CMD_ADD_QUEUE
>   */
>  
>  #ifndef _LINUX_FUSE_H
> @@ -275,7 +278,7 @@
>  #define FUSE_KERNEL_VERSION 7
>  
>  /** Minor version number of this interface */
> -#define FUSE_KERNEL_MINOR_VERSION 45
> +#define FUSE_KERNEL_MINOR_VERSION 46
>  
>  /** The node ID of the root inode */
>  #define FUSE_ROOT_ID 1
> @@ -1292,6 +1295,9 @@ enum fuse_uring_cmd {
>  
>  	/* commit fuse request result and fetch next request */
>  	FUSE_IO_URING_CMD_COMMIT_AND_FETCH = 2,
> +
> +	/* add a queue */
> +	FUSE_IO_URING_CMD_ADD_QUEUE = 3,
>  };
>  
>  /**


Reviewed-by: Bernd Schubert <[email protected]>