Re: [PATCH v10 10/17] fuse: Add io-uring sqe commit and fetch support

Luis Henriques
2025-01-22T15:56:52Z

On Mon, Jan 20 2025, Bernd Schubert wrote:

> This adds support for fuse request completion through ring SQEs
> (FUSE_URING_CMD_COMMIT_AND_FETCH handling). After committing
> the ring entry it becomes available for new fuse requests.
> Handling of requests through the ring (SQE/CQE handling)
> is complete now.
>
> Fuse request data are copied through the mmaped ring buffer,
> there is no support for any zero copy yet.

Single comment below.

> Signed-off-by: Bernd Schubert <bschubert@ddn.com>
> Reviewed-by: Pavel Begunkov <asml.silence@gmail.com> # io_uring
> ---
> fs/fuse/dev_uring.c | 448 ++++++++++++++++++++++++++++++++++++++++++++++++++
> fs/fuse/dev_uring_i.h | 12 ++
> fs/fuse/fuse_i.h | 4 +
> 3 files changed, 464 insertions(+)
>
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> index 60e38ff1ecef3b007bae7ceedd7dd997439e463a..74aa5ccaff30998cf58e805f7c1b7ebf70d5cd6d 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -24,6 +24,18 @@ bool fuse_uring_enabled(void)
> return enable_uring;
> }
>
> +static void fuse_uring_req_end(struct fuse_ring_ent *ent, int error)
> +{
> + struct fuse_req *req = ent->fuse_req;
> +
> + if (error)
> + req->out.h.error = error;
> +
> + clear_bit(FR_SENT, &req->flags);
> + fuse_request_end(ent->fuse_req);
> + ent->fuse_req = NULL;
> +}
> +
> void fuse_uring_destruct(struct fuse_conn *fc)
> {
> struct fuse_ring *ring = fc->ring;
> @@ -39,8 +51,11 @@ void fuse_uring_destruct(struct fuse_conn *fc)
> continue;
>
> WARN_ON(!list_empty(&queue->ent_avail_queue));
> + WARN_ON(!list_empty(&queue->ent_w_req_queue));
> WARN_ON(!list_empty(&queue->ent_commit_queue));
> + WARN_ON(!list_empty(&queue->ent_in_userspace));
>
> + kfree(queue->fpq.processing);
> kfree(queue);
> ring->queues[qid] = NULL;
> }
> @@ -99,20 +114,34 @@ static struct fuse_ring_queue *fuse_uring_create_queue(struct fuse_ring *ring,
> {
> struct fuse_conn *fc = ring->fc;
> struct fuse_ring_queue *queue;
> + struct list_head *pq;
>
> queue = kzalloc(sizeof(*queue), GFP_KERNEL_ACCOUNT);
> if (!queue)
> return NULL;
> + pq = kcalloc(FUSE_PQ_HASH_SIZE, sizeof(struct list_head), GFP_KERNEL);
> + if (!pq) {
> + kfree(queue);
> + return NULL;
> + }
> +
> queue->qid = qid;
> queue->ring = ring;
> spin_lock_init(&queue->lock);
>
> INIT_LIST_HEAD(&queue->ent_avail_queue);
> INIT_LIST_HEAD(&queue->ent_commit_queue);
> + INIT_LIST_HEAD(&queue->ent_w_req_queue);
> + INIT_LIST_HEAD(&queue->ent_in_userspace);
> + INIT_LIST_HEAD(&queue->fuse_req_queue);
> +
> + queue->fpq.processing = pq;
> + fuse_pqueue_init(&queue->fpq);
>
> spin_lock(&fc->lock);
> if (ring->queues[qid]) {
> spin_unlock(&fc->lock);
> + kfree(queue->fpq.processing);
> kfree(queue);
> return ring->queues[qid];
> }
> @@ -126,6 +155,213 @@ static struct fuse_ring_queue *fuse_uring_create_queue(struct fuse_ring *ring,
> return queue;
> }
>
> +/*
> + * Checks for errors and stores it into the request
> + */
> +static int fuse_uring_out_header_has_err(struct fuse_out_header *oh,
> + struct fuse_req *req,
> + struct fuse_conn *fc)
> +{
> + int err;
> +
> + err = -EINVAL;
> + if (oh->unique == 0) {
> + /* Not supported through io-uring yet */
> + pr_warn_once("notify through fuse-io-uring not supported\n");
> + goto err;
> + }
> +
> + if (oh->error <= -ERESTARTSYS || oh->error > 0)
> + goto err;
> +
> + if (oh->error) {
> + err = oh->error;
> + goto err;
> + }
> +
> + err = -ENOENT;
> + if ((oh->unique & ~FUSE_INT_REQ_BIT) != req->in.h.unique) {
> + pr_warn_ratelimited("unique mismatch, expected: %llu got %llu\n",
> + req->in.h.unique,
> + oh->unique & ~FUSE_INT_REQ_BIT);
> + goto err;
> + }
> +
> + /*
> + * Is it an interrupt reply ID?
> + * XXX: Not supported through fuse-io-uring yet, it should not even
> + * find the request - should not happen.
> + */
> + WARN_ON_ONCE(oh->unique & FUSE_INT_REQ_BIT);
> +
> + err = 0;
> +err:
> + return err;
> +}
> +
> +static int fuse_uring_copy_from_ring(struct fuse_ring *ring,
> + struct fuse_req *req,
> + struct fuse_ring_ent *ent)
> +{
> + struct fuse_copy_state cs;
> + struct fuse_args *args = req->args;
> + struct iov_iter iter;
> + int err;
> + struct fuse_uring_ent_in_out ring_in_out;
> +
> + err = copy_from_user(&ring_in_out, &ent->headers->ring_ent_in_out,
> + sizeof(ring_in_out));
> + if (err)
> + return -EFAULT;
> +
> + err = import_ubuf(ITER_SOURCE, ent->payload, ring->max_payload_sz,
> + &iter);
> + if (err)
> + return err;
> +
> + fuse_copy_init(&cs, 0, &iter);
> + cs.is_uring = 1;
> + cs.req = req;
> +
> + return fuse_copy_out_args(&cs, args, ring_in_out.payload_sz);
> +}
> +
> + /*
> + * Copy data from the req to the ring buffer
> + */
> +static int fuse_uring_args_to_ring(struct fuse_ring *ring, struct fuse_req *req,
> + struct fuse_ring_ent *ent)
> +{
> + struct fuse_copy_state cs;
> + struct fuse_args *args = req->args;
> + struct fuse_in_arg *in_args = args->in_args;
> + int num_args = args->in_numargs;
> + int err;
> + struct iov_iter iter;
> + struct fuse_uring_ent_in_out ent_in_out = {
> + .flags = 0,
> + .commit_id = req->in.h.unique,
> + };
> +
> + err = import_ubuf(ITER_DEST, ent->payload, ring->max_payload_sz, &iter);
> + if (err) {
> + pr_info_ratelimited("fuse: Import of user buffer failed\n");
> + return err;
> + }
> +
> + fuse_copy_init(&cs, 1, &iter);
> + cs.is_uring = 1;
> + cs.req = req;
> +
> + if (num_args > 0) {
> + /*
> + * Expectation is that the first argument is the per op header.
> + * Some op code have that as zero size.
> + */
> + if (args->in_args[0].size > 0) {
> + err = copy_to_user(&ent->headers->op_in, in_args->value,
> + in_args->size);
> + if (err) {
> + pr_info_ratelimited(
> + "Copying the header failed.\n");
> + return -EFAULT;
> + }
> + }
> + in_args++;
> + num_args--;
> + }
> +
> + /* copy the payload */
> + err = fuse_copy_args(&cs, num_args, args->in_pages,
> + (struct fuse_arg *)in_args, 0);
> + if (err) {
> + pr_info_ratelimited("%s fuse_copy_args failed\n", __func__);
> + return err;
> + }
> +
> + ent_in_out.payload_sz = cs.ring.copied_sz;
> + err = copy_to_user(&ent->headers->ring_ent_in_out, &ent_in_out,
> + sizeof(ent_in_out));
> + return err ? -EFAULT : 0;
> +}
> +
> +static int fuse_uring_copy_to_ring(struct fuse_ring_ent *ent,
> + struct fuse_req *req)
> +{
> + struct fuse_ring_queue *queue = ent->queue;
> + struct fuse_ring *ring = queue->ring;
> + int err;
> +
> + err = -EIO;
> + if (WARN_ON(ent->state != FRRS_FUSE_REQ)) {
> + pr_err("qid=%d ring-req=%p invalid state %d on send\n",
> + queue->qid, ent, ent->state);
> + return err;
> + }
> +
> + err = -EINVAL;
> + if (WARN_ON(req->in.h.unique == 0))
> + return err;
> +
> + /* copy the request */
> + err = fuse_uring_args_to_ring(ring, req, ent);
> + if (unlikely(err)) {
> + pr_info_ratelimited("Copy to ring failed: %d\n", err);
> + return err;
> + }
> +
> + /* copy fuse_in_header */
> + err = copy_to_user(&ent->headers->in_out, &req->in.h,
> + sizeof(req->in.h));
> + if (err) {
> + err = -EFAULT;
> + return err;
> + }
> +
> + return 0;
> +}
> +
> +static int fuse_uring_prepare_send(struct fuse_ring_ent *ent)
> +{
> + struct fuse_req *req = ent->fuse_req;
> + int err;
> +
> + err = fuse_uring_copy_to_ring(ent, req);
> + if (!err)
> + set_bit(FR_SENT, &req->flags);
> + else
> + fuse_uring_req_end(ent, err);
> +
> + return err;
> +}
> +
> +/*
> + * Write data to the ring buffer and send the request to userspace,
> + * userspace will read it
> + * This is comparable with classical read(/dev/fuse)
> + */
> +static int fuse_uring_send_next_to_ring(struct fuse_ring_ent *ent,
> + unsigned int issue_flags)
> +{
> + struct fuse_ring_queue *queue = ent->queue;
> + int err;
> + struct io_uring_cmd *cmd;
> +
> + err = fuse_uring_prepare_send(ent);
> + if (err)
> + return err;
> +
> + spin_lock(&queue->lock);
> + cmd = ent->cmd;
> + ent->cmd = NULL;
> + ent->state = FRRS_USERSPACE;
> + list_move(&ent->list, &queue->ent_in_userspace);
> + spin_unlock(&queue->lock);
> +
> + io_uring_cmd_done(cmd, 0, 0, issue_flags);
> + return 0;
> +}
> +
> /*
> * Make a ring entry available for fuse_req assignment
> */
> @@ -137,6 +373,210 @@ static void fuse_uring_ent_avail(struct fuse_ring_ent *ent,
> ent->state = FRRS_AVAILABLE;
> }
>
> +/* Used to find the request on SQE commit */
> +static void fuse_uring_add_to_pq(struct fuse_ring_ent *ent,
> + struct fuse_req *req)
> +{
> + struct fuse_ring_queue *queue = ent->queue;
> + struct fuse_pqueue *fpq = &queue->fpq;
> + unsigned int hash;
> +
> + req->ring_entry = ent;
> + hash = fuse_req_hash(req->in.h.unique);
> + list_move_tail(&req->list, &fpq->processing[hash]);
> +}
> +
> +/*
> + * Assign a fuse queue entry to the given entry
> + */
> +static void fuse_uring_add_req_to_ring_ent(struct fuse_ring_ent *ent,
> + struct fuse_req *req)
> +{
> + struct fuse_ring_queue *queue = ent->queue;
> + struct fuse_conn *fc = req->fm->fc;
> + struct fuse_iqueue *fiq = &fc->iq;
> +
> + lockdep_assert_held(&queue->lock);
> +
> + if (WARN_ON_ONCE(ent->state != FRRS_AVAILABLE &&
> + ent->state != FRRS_COMMIT)) {
> + pr_warn("%s qid=%d state=%d\n", __func__, ent->queue->qid,
> + ent->state);
> + }
> +
> + spin_lock(&fiq->lock);
> + clear_bit(FR_PENDING, &req->flags);
> + spin_unlock(&fiq->lock);
> + ent->fuse_req = req;
> + ent->state = FRRS_FUSE_REQ;
> + list_move(&ent->list, &queue->ent_w_req_queue);
> + fuse_uring_add_to_pq(ent, req);
> +}
> +
> +/*
> + * Release the ring entry and fetch the next fuse request if available
> + *
> + * @return true if a new request has been fetched
> + */
> +static bool fuse_uring_ent_assign_req(struct fuse_ring_ent *ent)
> + __must_hold(&queue->lock)
> +{
> + struct fuse_req *req;
> + struct fuse_ring_queue *queue = ent->queue;
> + struct list_head *req_queue = &queue->fuse_req_queue;
> +
> + lockdep_assert_held(&queue->lock);
> +
> + /* get and assign the next entry while it is still holding the lock */
> + req = list_first_entry_or_null(req_queue, struct fuse_req, list);
> + if (req) {
> + fuse_uring_add_req_to_ring_ent(ent, req);
> + return true;
> + }
> +
> + return false;
> +}
> +
> +/*
> + * Read data from the ring buffer, which user space has written to
> + * This is comparible with handling of classical write(/dev/fuse).
> + * Also make the ring request available again for new fuse requests.
> + */
> +static void fuse_uring_commit(struct fuse_ring_ent *ent,
> + unsigned int issue_flags)
> +{
> + struct fuse_ring *ring = ent->queue->ring;
> + struct fuse_conn *fc = ring->fc;
> + struct fuse_req *req = ent->fuse_req;
> + ssize_t err = 0;
> +
> + err = copy_from_user(&req->out.h, &ent->headers->in_out,
> + sizeof(req->out.h));
> + if (err) {
> + req->out.h.error = err;

Shouldn't 'req->out.h.error' be set to -EFAULT instead?

Cheers,
--
Luís

> + goto out;
> + }
> +
> + err = fuse_uring_out_header_has_err(&req->out.h, req, fc);
> + if (err) {
> + /* req->out.h.error already set */
> + goto out;
> + }
> +
> + err = fuse_uring_copy_from_ring(ring, req, ent);
> +out:
> + fuse_uring_req_end(ent, err);
> +}
> +
> +/*
> + * Get the next fuse req and send it
> + */
> +static void fuse_uring_next_fuse_req(struct fuse_ring_ent *ent,
> + struct fuse_ring_queue *queue,
> + unsigned int issue_flags)
> +{
> + int err;
> + bool has_next;
> +
> +retry:
> + spin_lock(&queue->lock);
> + fuse_uring_ent_avail(ent, queue);
> + has_next = fuse_uring_ent_assign_req(ent);
> + spin_unlock(&queue->lock);
> +
> + if (has_next) {
> + err = fuse_uring_send_next_to_ring(ent, issue_flags);
> + if (err)
> + goto retry;
> + }
> +}
> +
> +static int fuse_ring_ent_set_commit(struct fuse_ring_ent *ent)
> +{
> + struct fuse_ring_queue *queue = ent->queue;
> +
> + lockdep_assert_held(&queue->lock);
> +
> + if (WARN_ON_ONCE(ent->state != FRRS_USERSPACE))
> + return -EIO;
> +
> + ent->state = FRRS_COMMIT;
> + list_move(&ent->list, &queue->ent_commit_queue);
> +
> + return 0;
> +}
> +
> +/* FUSE_URING_CMD_COMMIT_AND_FETCH handler */
> +static int fuse_uring_commit_fetch(struct io_uring_cmd *cmd, int issue_flags,
> + struct fuse_conn *fc)
> +{
> + const struct fuse_uring_cmd_req *cmd_req = io_uring_sqe_cmd(cmd->sqe);
> + struct fuse_ring_ent *ent;
> + int err;
> + struct fuse_ring *ring = fc->ring;
> + struct fuse_ring_queue *queue;
> + uint64_t commit_id = READ_ONCE(cmd_req->commit_id);
> + unsigned int qid = READ_ONCE(cmd_req->qid);
> + struct fuse_pqueue *fpq;
> + struct fuse_req *req;
> +
> + err = -ENOTCONN;
> + if (!ring)
> + return err;
> +
> + if (qid >= ring->nr_queues)
> + return -EINVAL;
> +
> + queue = ring->queues[qid];
> + if (!queue)
> + return err;
> + fpq = &queue->fpq;
> +
> + spin_lock(&queue->lock);
> + /* Find a request based on the unique ID of the fuse request
> + * This should get revised, as it needs a hash calculation and list
> + * search. And full struct fuse_pqueue is needed (memory overhead).
> + * As well as the link from req to ring_ent.
> + */
> + req = fuse_request_find(fpq, commit_id);
> + err = -ENOENT;
> + if (!req) {
> + pr_info("qid=%d commit_id %llu not found\n", queue->qid,
> + commit_id);
> + spin_unlock(&queue->lock);
> + return err;
> + }
> + list_del_init(&req->list);
> + ent = req->ring_entry;
> + req->ring_entry = NULL;
> +
> + err = fuse_ring_ent_set_commit(ent);
> + if (err != 0) {
> + pr_info_ratelimited("qid=%d commit_id %llu state %d",
> + queue->qid, commit_id, ent->state);
> + spin_unlock(&queue->lock);
> + req->out.h.error = err;
> + clear_bit(FR_SENT, &req->flags);
> + fuse_request_end(req);
> + return err;
> + }
> +
> + ent->cmd = cmd;
> + spin_unlock(&queue->lock);
> +
> + /* without the queue lock, as other locks are taken */
> + fuse_uring_commit(ent, issue_flags);
> +
> + /*
> + * Fetching the next request is absolutely required as queued
> + * fuse requests would otherwise not get processed - committing
> + * and fetching is done in one step vs legacy fuse, which has separated
> + * read (fetch request) and write (commit result).
> + */
> + fuse_uring_next_fuse_req(ent, queue, issue_flags);
> + return 0;
> +}
> +
> /*
> * fuse_uring_req_fetch command handling
> */
> @@ -318,6 +758,14 @@ int __maybe_unused fuse_uring_cmd(struct io_uring_cmd *cmd,
> return err;
> }
> break;
> + case FUSE_IO_URING_CMD_COMMIT_AND_FETCH:
> + err = fuse_uring_commit_fetch(cmd, issue_flags, fc);
> + if (err) {
> + pr_info_once("FUSE_IO_URING_COMMIT_AND_FETCH failed err=%d\n",
> + err);
> + return err;
> + }
> + break;
> default:
> return -EINVAL;
> }
> diff --git a/fs/fuse/dev_uring_i.h b/fs/fuse/dev_uring_i.h
> index ae1536355b368583132d2ab6878b5490510b28e8..44bf237f0d5abcadbb768ba3940c3fec813b079d 100644
> --- a/fs/fuse/dev_uring_i.h
> +++ b/fs/fuse/dev_uring_i.h
> @@ -20,6 +20,9 @@ enum fuse_ring_req_state {
> /* The ring entry is waiting for new fuse requests */
> FRRS_AVAILABLE,
>
> + /* The ring entry got assigned a fuse req */
> + FRRS_FUSE_REQ,
> +
> /* The ring entry is in or on the way to user space */
> FRRS_USERSPACE,
> };
> @@ -67,7 +70,16 @@ struct fuse_ring_queue {
> * entries in the process of being committed or in the process
> * to be sent to userspace
> */
> + struct list_head ent_w_req_queue;
> struct list_head ent_commit_queue;
> +
> + /* entries in userspace */
> + struct list_head ent_in_userspace;
> +
> + /* fuse requests waiting for an entry slot */
> + struct list_head fuse_req_queue;
> +
> + struct fuse_pqueue fpq;
> };
>
> /**
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index e545b0864dd51e82df61cc39bdf65d3d36a418dc..e71556894bc25808581424ec7bdd4afeebc81f15 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -438,6 +438,10 @@ struct fuse_req {
>
> /** fuse_mount this request belongs to */
> struct fuse_mount *fm;
> +
> +#ifdef CONFIG_FUSE_IO_URING
> + void *ring_entry;
> +#endif
> };
>
> struct fuse_iqueue;
>
> --
> 2.43.0
>