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

[Bernd Schubert]

On 4/1/26 10:40, Li Wang wrote:
> 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,

I will check the other parts more thoroughly in the evening, but please
take a look into fuse_uring_register(), it also also overrides other
pointers at startup - I would like leave it here as it is, move the
function above into dev_uring.c and then update this part in dev_uring.c

static const struct fuse_iqueue_ops fuse_io_uring_ops = {
        /* should be send over io-uring as enhancement */
        .send_forget = fuse_dev_queue_forget,


Thanks,
Bernd