fuse: Allow to queue fg requests through io-uring

This prepares queueing and sending foreground requests through
io-uring.

Signed-off-by: Bernd Schubert <bschubert@ddn.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com> # io_uring
Reviewed-by: Luis Henriques <luis@igalia.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dev_uring.c

@@ -24,6 +24,29 @@ bool fuse_uring_enabled(void)
 	return enable_uring;
 }
 
+struct fuse_uring_pdu {
+	struct fuse_ring_ent *ent;
+};
+
+static const struct fuse_iqueue_ops fuse_io_uring_ops;
+
+static void uring_cmd_set_ring_ent(struct io_uring_cmd *cmd,
+				   struct fuse_ring_ent *ring_ent)
+{
+	struct fuse_uring_pdu *pdu =
+		io_uring_cmd_to_pdu(cmd, struct fuse_uring_pdu);
+
+	pdu->ent = ring_ent;
+}
+
+static struct fuse_ring_ent *uring_cmd_to_ring_ent(struct io_uring_cmd *cmd)
+{
+	struct fuse_uring_pdu *pdu =
+		io_uring_cmd_to_pdu(cmd, struct fuse_uring_pdu);
+
+	return pdu->ent;
+}
+
 static void fuse_uring_req_end(struct fuse_ring_ent *ent, struct fuse_req *req,
 			       int error)
 {
@@ -776,6 +799,31 @@ 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->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
  */
@@ -784,11 +832,23 @@ static void fuse_uring_do_register(struct fuse_ring_ent *ent,
 				   unsigned int issue_flags)
 {
 	struct fuse_ring_queue *queue = ent->queue;
+	struct fuse_ring *ring = queue->ring;
+	struct fuse_conn *fc = ring->fc;
+	struct fuse_iqueue *fiq = &fc->iq;
 
 	spin_lock(&queue->lock);
 	ent->cmd = cmd;
 	fuse_uring_ent_avail(ent, queue);
 	spin_unlock(&queue->lock);
+
+	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);
+		}
+	}
 }
 
 /*
@@ -972,3 +1032,123 @@ int __maybe_unused fuse_uring_cmd(struct io_uring_cmd *cmd,
 
 	return -EIOCBQUEUED;
 }
+
+static void fuse_uring_send(struct fuse_ring_ent *ent, struct io_uring_cmd *cmd,
+			    ssize_t ret, unsigned int issue_flags)
+{
+	struct fuse_ring_queue *queue = ent->queue;
+
+	spin_lock(&queue->lock);
+	ent->state = FRRS_USERSPACE;
+	list_move(&ent->list, &queue->ent_in_userspace);
+	ent->cmd = NULL;
+	spin_unlock(&queue->lock);
+
+	io_uring_cmd_done(cmd, ret, 0, issue_flags);
+}
+
+/*
+ * This prepares and sends the ring request in fuse-uring task context.
+ * User buffers are not mapped yet - the application does not have permission
+ * to write to it - this has to be executed in ring task context.
+ */
+static void fuse_uring_send_in_task(struct io_uring_cmd *cmd,
+				    unsigned int issue_flags)
+{
+	struct fuse_ring_ent *ent = uring_cmd_to_ring_ent(cmd);
+	struct fuse_ring_queue *queue = ent->queue;
+	int err;
+
+	if (!(issue_flags & IO_URING_F_TASK_DEAD)) {
+		err = fuse_uring_prepare_send(ent, ent->fuse_req);
+		if (err) {
+			fuse_uring_next_fuse_req(ent, queue, issue_flags);
+			return;
+		}
+	} else {
+		err = -ECANCELED;
+	}
+
+	fuse_uring_send(ent, cmd, err, issue_flags);
+}
+
+static struct fuse_ring_queue *fuse_uring_task_to_queue(struct fuse_ring *ring)
+{
+	unsigned int qid;
+	struct fuse_ring_queue *queue;
+
+	qid = task_cpu(current);
+
+	if (WARN_ONCE(qid >= ring->nr_queues,
+		      "Core number (%u) exceeds nr queues (%zu)\n", qid,
+		      ring->nr_queues))
+		qid = 0;
+
+	queue = ring->queues[qid];
+	WARN_ONCE(!queue, "Missing queue for qid %d\n", qid);
+
+	return queue;
+}
+
+static void fuse_uring_dispatch_ent(struct fuse_ring_ent *ent)
+{
+	struct io_uring_cmd *cmd = ent->cmd;
+
+	uring_cmd_set_ring_ent(cmd, ent);
+	io_uring_cmd_complete_in_task(cmd, fuse_uring_send_in_task);
+}
+
+/* queue a fuse request and send it if a ring entry is available */
+void fuse_uring_queue_fuse_req(struct fuse_iqueue *fiq, struct fuse_req *req)
+{
+	struct fuse_conn *fc = req->fm->fc;
+	struct fuse_ring *ring = fc->ring;
+	struct fuse_ring_queue *queue;
+	struct fuse_ring_ent *ent = NULL;
+	int err;
+
+	err = -EINVAL;
+	queue = fuse_uring_task_to_queue(ring);
+	if (!queue)
+		goto err;
+
+	if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
+		req->in.h.unique = fuse_get_unique(fiq);
+
+	spin_lock(&queue->lock);
+	err = -ENOTCONN;
+	if (unlikely(queue->stopped))
+		goto err_unlock;
+
+	ent = list_first_entry_or_null(&queue->ent_avail_queue,
+				       struct fuse_ring_ent, list);
+	if (ent)
+		fuse_uring_add_req_to_ring_ent(ent, req);
+	else
+		list_add_tail(&req->list, &queue->fuse_req_queue);
+	spin_unlock(&queue->lock);
+
+	if (ent)
+		fuse_uring_dispatch_ent(ent);
+
+	return;
+
+err_unlock:
+	spin_unlock(&queue->lock);
+err:
+	req->out.h.error = err;
+	clear_bit(FR_PENDING, &req->flags);
+	fuse_request_end(req);
+}
+
+static const struct fuse_iqueue_ops fuse_io_uring_ops = {
+	/* should be send over io-uring as enhancement */
+	.send_forget = fuse_dev_queue_forget,
+
+	/*
+	 * could be send over io-uring, but interrupts should be rare,
+	 * no need to make the code complex
+	 */
+	.send_interrupt = fuse_dev_queue_interrupt,
+	.send_req = fuse_uring_queue_fuse_req,
+};

fs/fuse/dev_uring_i.h

@@ -117,6 +117,8 @@ struct fuse_ring {
 	unsigned long teardown_time;
 
 	atomic_t queue_refs;
+
+	bool ready;
 };
 
 bool fuse_uring_enabled(void);
@@ -124,6 +126,7 @@ void fuse_uring_destruct(struct fuse_conn *fc);
 void fuse_uring_stop_queues(struct fuse_ring *ring);
 void fuse_uring_abort_end_requests(struct fuse_ring *ring);
 int fuse_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags);
+void fuse_uring_queue_fuse_req(struct fuse_iqueue *fiq, struct fuse_req *req);
 
 static inline void fuse_uring_abort(struct fuse_conn *fc)
 {
@@ -147,6 +150,11 @@ static inline void fuse_uring_wait_stopped_queues(struct fuse_conn *fc)
 			   atomic_read(&ring->queue_refs) == 0);
 }
 
+static inline bool fuse_uring_ready(struct fuse_conn *fc)
+{
+	return fc->ring && fc->ring->ready;
+}
+
 #else /* CONFIG_FUSE_IO_URING */
 
 struct fuse_ring;