[PATCH] fuse: Send FORGET over io_uring when ring is ready

[Li Wang]

Once the FUSE io_uring is registered and marked ready, most request
types are delivered through io_uring, while FORGET notifications were still
queued with fuse_dev_queue_forget() and only consumed through the legacy
path on /dev/fuse.

Deliver single FORGET operations through fuse_uring_queue_fuse_req() when
the ring is ready. Otherwise, fall back to fuse_dev_queue_forget()
so behavior matches the previous implementation.

Benefits:
- While io-uring is active, the daemon can handle forgets in the same
  commit/fetch loop as other opcodes instead of also draining a separate
  /dev/fuse read path for forget traffic.
- Reduces split-brain transport for high-volume forgets (eviction,
  unmount) when the ring is already the primary channel, which simplifies
  userspace and keeps teardown forgets on the same completion path as
  other uring-backed work.
- Reuses the same per-queue io-uring machinery and noreply/force request
  setup (creds, FR_WAITING/FR_FORCE, etc.) already used for similar
  kernel-initiated traffic.

Signed-off-by: Li Wang <liwang@xxxxxxxxxx>
---
 fs/fuse/dev.c        | 84 ++++++++++++++++++++++++++++++++++++++++++++
 fs/fuse/dev_uring.c  |  2 +-
 fs/fuse/fuse_dev_i.h |  4 +++
 3 files changed, 89 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index b212565a78cf..f58abc80fd7b 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -665,6 +665,90 @@ static void fuse_args_to_req(struct fuse_req *req, struct fuse_args *args)
 		__set_bit(FR_ASYNC, &req->flags);
 }
 
+#ifdef CONFIG_FUSE_IO_URING
+struct fuse_forget_uring_data {
+	struct fuse_args args;
+	struct fuse_forget_in inarg;
+};
+
+static void fuse_forget_uring_free(struct fuse_mount *fm, struct fuse_args *args,
+				   int error)
+{
+	struct fuse_forget_uring_data *d =
+		container_of(args, struct fuse_forget_uring_data, args);
+
+	kfree(d);
+}
+
+/*
+ * Send FUSE_FORGET through the io-uring ring when active; same payload as
+ * fuse_read_single_forget(), with userspace committing like any other request.
+ */
+void fuse_io_uring_send_forget(struct fuse_iqueue *fiq,
+				struct fuse_forget_link *forget)
+{
+	struct fuse_conn *fc = container_of(fiq, struct fuse_conn, iq);
+	struct fuse_mount *fm;
+	struct fuse_req *req;
+	struct fuse_forget_uring_data *d;
+
+	if (!fuse_uring_ready(fc)) {
+		fuse_dev_queue_forget(fiq, forget);
+		return;
+	}
+
+	down_read(&fc->killsb);
+	if (list_empty(&fc->mounts)) {
+		up_read(&fc->killsb);
+		fuse_dev_queue_forget(fiq, forget);
+		return;
+	}
+	fm = list_first_entry(&fc->mounts, struct fuse_mount, fc_entry);
+	up_read(&fc->killsb);
+
+	d = kmalloc(sizeof(*d), GFP_KERNEL);
+	if (!d)
+		goto fallback;
+
+	atomic_inc(&fc->num_waiting);
+	req = fuse_request_alloc(fm, GFP_KERNEL);
+	if (!req) {
+		kfree(d);
+		fuse_drop_waiting(fc);
+		goto fallback;
+	}
+
+	memset(&d->args, 0, sizeof(d->args));
+	d->inarg.nlookup = forget->forget_one.nlookup;
+	d->args.opcode = FUSE_FORGET;
+	d->args.nodeid = forget->forget_one.nodeid;
+	d->args.in_numargs = 1;
+	d->args.in_args[0].size = sizeof(d->inarg);
+	d->args.in_args[0].value = &d->inarg;
+	d->args.force = true;
+	d->args.noreply = true;
+	d->args.end = fuse_forget_uring_free;
+
+	kfree(forget);
+
+	fuse_force_creds(req);
+	__set_bit(FR_WAITING, &req->flags);
+	if (!d->args.abort_on_kill)
+		__set_bit(FR_FORCE, &req->flags);
+	fuse_adjust_compat(fc, &d->args);
+	fuse_args_to_req(req, &d->args);
+	req->in.h.len = sizeof(struct fuse_in_header) +
+		fuse_len_args(req->args->in_numargs,
+			      (struct fuse_arg *)req->args->in_args);
+
+	fuse_uring_queue_fuse_req(fiq, req);
+	return;
+
+fallback:
+	fuse_dev_queue_forget(fiq, forget);
+}
+#endif
+
 ssize_t __fuse_simple_request(struct mnt_idmap *idmap,
 			      struct fuse_mount *fm,
 			      struct fuse_args *args)
diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
index 7b9822e8837b..a96539ea400a 100644
--- a/fs/fuse/dev_uring.c
+++ b/fs/fuse/dev_uring.c
@@ -1360,7 +1360,7 @@ bool fuse_uring_remove_pending_req(struct fuse_req *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,
+	.send_forget = fuse_io_uring_send_forget,
 
 	/*
 	 * could be send over io-uring, but interrupts should be rare,
diff --git a/fs/fuse/fuse_dev_i.h b/fs/fuse/fuse_dev_i.h
index 134bf44aff0d..264a25d7e47a 100644
--- a/fs/fuse/fuse_dev_i.h
+++ b/fs/fuse/fuse_dev_i.h
@@ -70,6 +70,10 @@ int fuse_copy_out_args(struct fuse_copy_state *cs, struct fuse_args *args,
 		       unsigned int nbytes);
 void fuse_dev_queue_forget(struct fuse_iqueue *fiq,
 			   struct fuse_forget_link *forget);
+#ifdef CONFIG_FUSE_IO_URING
+void fuse_io_uring_send_forget(struct fuse_iqueue *fiq,
+			       struct fuse_forget_link *forget);
+#endif
 void fuse_dev_queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req);
 bool fuse_remove_pending_req(struct fuse_req *req, spinlock_t *lock);
 
-- 
2.34.1