Re: [PATCH v10 06/17] fuse: {io-uring} Handle SQEs - register commands

Luis Henriques
2025-01-22T15:57:11Z

On Mon, Jan 20 2025, Bernd Schubert wrote:

> This adds basic support for ring SQEs (with opcode=IORING_OP_URING_CMD).
> For now only FUSE_IO_URING_CMD_REGISTER is handled to register queue
> entries.

Three comments below.

> Signed-off-by: Bernd Schubert <bschubert@ddn.com>
> Reviewed-by: Pavel Begunkov <asml.silence@gmail.com> # io_uring
> ---
> fs/fuse/Kconfig | 12 ++
> fs/fuse/Makefile | 1 +
> fs/fuse/dev_uring.c | 326 ++++++++++++++++++++++++++++++++++++++++++++++
> fs/fuse/dev_uring_i.h | 113 ++++++++++++++++
> fs/fuse/fuse_i.h | 5 +
> fs/fuse/inode.c | 10 ++
> include/uapi/linux/fuse.h | 76 ++++++++++-
> 7 files changed, 542 insertions(+), 1 deletion(-)
>
> diff --git a/fs/fuse/Kconfig b/fs/fuse/Kconfig
> index 8674dbfbe59dbf79c304c587b08ebba3cfe405be..ca215a3cba3e310d1359d069202193acdcdb172b 100644
> --- a/fs/fuse/Kconfig
> +++ b/fs/fuse/Kconfig
> @@ -63,3 +63,15 @@ config FUSE_PASSTHROUGH
> to be performed directly on a backing file.
>
> If you want to allow passthrough operations, answer Y.
> +
> +config FUSE_IO_URING
> + bool "FUSE communication over io-uring"
> + default y
> + depends on FUSE_FS
> + depends on IO_URING
> + help
> + This allows sending FUSE requests over the io-uring interface and
> + also adds request core affinity.
> +
> + If you want to allow fuse server/client communication through io-uring,
> + answer Y
> diff --git a/fs/fuse/Makefile b/fs/fuse/Makefile
> index 2c372180d631eb340eca36f19ee2c2686de9714d..3f0f312a31c1cc200c0c91a086b30a8318e39d94 100644
> --- a/fs/fuse/Makefile
> +++ b/fs/fuse/Makefile
> @@ -15,5 +15,6 @@ fuse-y += iomode.o
> fuse-$(CONFIG_FUSE_DAX) += dax.o
> fuse-$(CONFIG_FUSE_PASSTHROUGH) += passthrough.o
> fuse-$(CONFIG_SYSCTL) += sysctl.o
> +fuse-$(CONFIG_FUSE_IO_URING) += dev_uring.o
>
> virtiofs-y := virtio_fs.o
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..60e38ff1ecef3b007bae7ceedd7dd997439e463a
> --- /dev/null
> +++ b/fs/fuse/dev_uring.c
> @@ -0,0 +1,326 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * FUSE: Filesystem in Userspace
> + * Copyright (c) 2023-2024 DataDirect Networks.
> + */
> +
> +#include "fuse_i.h"
> +#include "dev_uring_i.h"
> +#include "fuse_dev_i.h"
> +
> +#include <linux/fs.h>
> +#include <linux/io_uring/cmd.h>
> +
> +static bool __read_mostly enable_uring;
> +module_param(enable_uring, bool, 0644);

Allowing to change 'enable_uring' at runtime will cause troubles. I don't
think the code gracefully handles changes to this parameter. Maybe it
should be a read-only parameter. Another option would be to be proxy it
at the connection level, so that once enabled/disabled it will remain so
for the lifetime of that connection.

> +MODULE_PARM_DESC(enable_uring,
> + "Enable userspace communication through io-uring");
> +
> +#define FUSE_URING_IOV_SEGS 2 /* header and payload */
> +
> +
> +bool fuse_uring_enabled(void)
> +{
> + return enable_uring;
> +}
> +
>
> +void fuse_uring_destruct(struct fuse_conn *fc)
> +{
> + struct fuse_ring *ring = fc->ring;
> + int qid;
> +
> + if (!ring)
> + return;
> +
> + for (qid = 0; qid < ring->nr_queues; qid++) {
> + struct fuse_ring_queue *queue = ring->queues[qid];
> +
> + if (!queue)
> + continue;
> +
> + WARN_ON(!list_empty(&queue->ent_avail_queue));
> + WARN_ON(!list_empty(&queue->ent_commit_queue));
> +
> + kfree(queue);
> + ring->queues[qid] = NULL;
> + }
> +
> + kfree(ring->queues);
> + kfree(ring);
> + fc->ring = NULL;
> +}
> +
> +/*
> + * Basic ring setup for this connection based on the provided configuration
> + */
> +static struct fuse_ring *fuse_uring_create(struct fuse_conn *fc)
> +{
> + struct fuse_ring *ring;
> + size_t nr_queues = num_possible_cpus();
> + struct fuse_ring *res = NULL;
> + size_t max_payload_size;
> +
> + ring = kzalloc(sizeof(*fc->ring), GFP_KERNEL_ACCOUNT);
> + if (!ring)
> + return NULL;
> +
> + ring->queues = kcalloc(nr_queues, sizeof(struct fuse_ring_queue *),
> + GFP_KERNEL_ACCOUNT);
> + if (!ring->queues)
> + goto out_err;
> +
> + max_payload_size = max(FUSE_MIN_READ_BUFFER, fc->max_write);
> + max_payload_size = max(max_payload_size, fc->max_pages * PAGE_SIZE);
> +
> + spin_lock(&fc->lock);
> + if (fc->ring) {
> + /* race, another thread created the ring in the meantime */
> + spin_unlock(&fc->lock);
> + res = fc->ring;
> + goto out_err;
> + }
> +
> + fc->ring = ring;
> + ring->nr_queues = nr_queues;
> + ring->fc = fc;
> + ring->max_payload_sz = max_payload_size;
> +
> + spin_unlock(&fc->lock);
> + return ring;
> +
> +out_err:
> + kfree(ring->queues);
> + kfree(ring);
> + return res;
> +}
> +
> +static struct fuse_ring_queue *fuse_uring_create_queue(struct fuse_ring *ring,
> + int qid)
> +{
> + struct fuse_conn *fc = ring->fc;
> + struct fuse_ring_queue *queue;
> +
> + queue = kzalloc(sizeof(*queue), GFP_KERNEL_ACCOUNT);
> + if (!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);
> +
> + spin_lock(&fc->lock);
> + if (ring->queues[qid]) {
> + spin_unlock(&fc->lock);
> + kfree(queue);
> + return ring->queues[qid];
> + }
> +
> + /*
> + * write_once and lock as the caller mostly doesn't take the lock at all
> + */
> + WRITE_ONCE(ring->queues[qid], queue);
> + spin_unlock(&fc->lock);
> +
> + return queue;
> +}
> +
> +/*
> + * Make a ring entry available for fuse_req assignment
> + */
> +static void fuse_uring_ent_avail(struct fuse_ring_ent *ent,
> + struct fuse_ring_queue *queue)
> +{
> + WARN_ON_ONCE(!ent->cmd);
> + list_move(&ent->list, &queue->ent_avail_queue);
> + ent->state = FRRS_AVAILABLE;
> +}
> +
> +/*
> + * fuse_uring_req_fetch command handling
> + */
> +static void fuse_uring_do_register(struct fuse_ring_ent *ent,
> + struct io_uring_cmd *cmd,
> + unsigned int issue_flags)
> +{
> + struct fuse_ring_queue *queue = ent->queue;
> +
> + spin_lock(&queue->lock);
> + ent->cmd = cmd;
> + fuse_uring_ent_avail(ent, queue);
> + spin_unlock(&queue->lock);
> +}
> +
> +/*
> + * sqe->addr is a ptr to an iovec array, iov[0] has the headers, iov[1]
> + * the payload
> + */
> +static int fuse_uring_get_iovec_from_sqe(const struct io_uring_sqe *sqe,
> + struct iovec iov[FUSE_URING_IOV_SEGS])
> +{
> + struct iovec __user *uiov = u64_to_user_ptr(READ_ONCE(sqe->addr));
> + struct iov_iter iter;
> + ssize_t ret;
> +
> + if (sqe->len != FUSE_URING_IOV_SEGS)
> + return -EINVAL;
> +
> + /*
> + * Direction for buffer access will actually be READ and WRITE,
> + * using write for the import should include READ access as well.
> + */
> + ret = import_iovec(WRITE, uiov, FUSE_URING_IOV_SEGS,
> + FUSE_URING_IOV_SEGS, &iov, &iter);
> + if (ret < 0)
> + return ret;
> +
> + return 0;
> +}
> +
> +static struct fuse_ring_ent *
> +fuse_uring_create_ring_ent(struct io_uring_cmd *cmd,
> + struct fuse_ring_queue *queue)
> +{
> + struct fuse_ring *ring = queue->ring;
> + struct fuse_ring_ent *ent;
> + size_t payload_size;
> + struct iovec iov[FUSE_URING_IOV_SEGS];
> + int err;
> +
> + err = fuse_uring_get_iovec_from_sqe(cmd->sqe, iov);
> + if (err) {
> + pr_info_ratelimited("Failed to get iovec from sqe, err=%d\n",
> + err);
> + return ERR_PTR(err);
> + }
> +
> + err = -EINVAL;
> + if (iov[0].iov_len < sizeof(struct fuse_uring_req_header)) {
> + pr_info_ratelimited("Invalid header len %zu\n", iov[0].iov_len);
> + return ERR_PTR(err);
> + }
> +
> + payload_size = iov[1].iov_len;
> + if (payload_size < ring->max_payload_sz) {
> + pr_info_ratelimited("Invalid req payload len %zu\n",
> + payload_size);
> + return ERR_PTR(err);
> + }
> +
> + /*
> + * The created queue above does not need to be destructed in
> + * case of entry errors below, will be done at ring destruction time.
> + */

This comment should probably be moved down, into function
fuse_uring_register() where this code was in earlier versions of the
patchset.

> + err = -ENOMEM;
> + ent = kzalloc(sizeof(*ent), GFP_KERNEL_ACCOUNT);
> + if (!ent)
> + return ERR_PTR(err);
> +
> + INIT_LIST_HEAD(&ent->list);
> +
> + ent->queue = queue;
> + ent->headers = iov[0].iov_base;
> + ent->payload = iov[1].iov_base;
> +
> + return ent;
> +}
> +
> +/*
> + * Register header and payload buffer with the kernel and puts the
> + * entry as "ready to get fuse requests" on the queue
> + */
> +static int fuse_uring_register(struct io_uring_cmd *cmd,
> + unsigned int issue_flags, struct fuse_conn *fc)
> +{
> + const struct fuse_uring_cmd_req *cmd_req = io_uring_sqe_cmd(cmd->sqe);
> + struct fuse_ring *ring = fc->ring;
> + struct fuse_ring_queue *queue;
> + struct fuse_ring_ent *ent;
> + int err;
> + unsigned int qid = READ_ONCE(cmd_req->qid);
> +
> + err = -ENOMEM;
> + if (!ring) {
> + ring = fuse_uring_create(fc);
> + if (!ring)
> + return err;
> + }
> +
> + if (qid >= ring->nr_queues) {
> + pr_info_ratelimited("fuse: Invalid ring qid %u\n", qid);
> + return -EINVAL;
> + }
> +
> + err = -ENOMEM;

Not needed, 'err' is already set to this value.

Cheers,
--
Luís

> + queue = ring->queues[qid];
> + if (!queue) {
> + queue = fuse_uring_create_queue(ring, qid);
> + if (!queue)
> + return err;
> + }
> +
> + ent = fuse_uring_create_ring_ent(cmd, queue);
> + if (IS_ERR(ent))
> + return PTR_ERR(ent);
> +
> + fuse_uring_do_register(ent, cmd, issue_flags);
> +
> + return 0;
> +}
> +
> +/*
> + * Entry function from io_uring to handle the given passthrough command
> + * (op code IORING_OP_URING_CMD)
> + */
> +int __maybe_unused fuse_uring_cmd(struct io_uring_cmd *cmd,
> + unsigned int issue_flags)
> +{
> + struct fuse_dev *fud;
> + struct fuse_conn *fc;
> + u32 cmd_op = cmd->cmd_op;
> + int err;
> +
> + if (!enable_uring) {
> + pr_info_ratelimited("fuse-io-uring is disabled\n");
> + return -EOPNOTSUPP;
> + }
> +
> + /* This extra SQE size holds struct fuse_uring_cmd_req */
> + if (!(issue_flags & IO_URING_F_SQE128))
> + return -EINVAL;
> +
> + fud = fuse_get_dev(cmd->file);
> + if (!fud) {
> + pr_info_ratelimited("No fuse device found\n");
> + return -ENOTCONN;
> + }
> + fc = fud->fc;
> +
> + if (fc->aborted)
> + return -ECONNABORTED;
> + if (!fc->connected)
> + return -ENOTCONN;
> +
> + /*
> + * fuse_uring_register() needs the ring to be initialized,
> + * we need to know the max payload size
> + */
> + if (!fc->initialized)
> + return -EAGAIN;
> +
> + switch (cmd_op) {
> + case FUSE_IO_URING_CMD_REGISTER:
> + err = fuse_uring_register(cmd, issue_flags, fc);
> + if (err) {
> + pr_info_once("FUSE_IO_URING_CMD_REGISTER failed err=%d\n",
> + err);
> + return err;
> + }
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + return -EIOCBQUEUED;
> +}
> diff --git a/fs/fuse/dev_uring_i.h b/fs/fuse/dev_uring_i.h
> new file mode 100644
> index 0000000000000000000000000000000000000000..ae1536355b368583132d2ab6878b5490510b28e8
> --- /dev/null
> +++ b/fs/fuse/dev_uring_i.h
> @@ -0,0 +1,113 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + *
> + * FUSE: Filesystem in Userspace
> + * Copyright (c) 2023-2024 DataDirect Networks.
> + */
> +
> +#ifndef _FS_FUSE_DEV_URING_I_H
> +#define _FS_FUSE_DEV_URING_I_H
> +
> +#include "fuse_i.h"
> +
> +#ifdef CONFIG_FUSE_IO_URING
> +
> +enum fuse_ring_req_state {
> + FRRS_INVALID = 0,
> +
> + /* The ring entry received from userspace and it is being processed */
> + FRRS_COMMIT,
> +
> + /* The ring entry is waiting for new fuse requests */
> + FRRS_AVAILABLE,
> +
> + /* The ring entry is in or on the way to user space */
> + FRRS_USERSPACE,
> +};
> +
> +/** A fuse ring entry, part of the ring queue */
> +struct fuse_ring_ent {
> + /* userspace buffer */
> + struct fuse_uring_req_header __user *headers;
> + void __user *payload;
> +
> + /* the ring queue that owns the request */
> + struct fuse_ring_queue *queue;
> +
> + /* fields below are protected by queue->lock */
> +
> + struct io_uring_cmd *cmd;
> +
> + struct list_head list;
> +
> + enum fuse_ring_req_state state;
> +
> + struct fuse_req *fuse_req;
> +};
> +
> +struct fuse_ring_queue {
> + /*
> + * back pointer to the main fuse uring structure that holds this
> + * queue
> + */
> + struct fuse_ring *ring;
> +
> + /* queue id, corresponds to the cpu core */
> + unsigned int qid;
> +
> + /*
> + * queue lock, taken when any value in the queue changes _and_ also
> + * a ring entry state changes.
> + */
> + spinlock_t lock;
> +
> + /* available ring entries (struct fuse_ring_ent) */
> + struct list_head ent_avail_queue;
> +
> + /*
> + * entries in the process of being committed or in the process
> + * to be sent to userspace
> + */
> + struct list_head ent_commit_queue;
> +};
> +
> +/**
> + * Describes if uring is for communication and holds alls the data needed
> + * for uring communication
> + */
> +struct fuse_ring {
> + /* back pointer */
> + struct fuse_conn *fc;
> +
> + /* number of ring queues */
> + size_t nr_queues;
> +
> + /* maximum payload/arg size */
> + size_t max_payload_sz;
> +
> + struct fuse_ring_queue **queues;
> +};
> +
> +bool fuse_uring_enabled(void);
> +void fuse_uring_destruct(struct fuse_conn *fc);
> +int fuse_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags);
> +
> +#else /* CONFIG_FUSE_IO_URING */
> +
> +struct fuse_ring;
> +
> +static inline void fuse_uring_create(struct fuse_conn *fc)
> +{
> +}
> +
> +static inline void fuse_uring_destruct(struct fuse_conn *fc)
> +{
> +}
> +
> +static inline bool fuse_uring_enabled(void)
> +{
> + return false;
> +}
> +
> +#endif /* CONFIG_FUSE_IO_URING */
> +
> +#endif /* _FS_FUSE_DEV_URING_I_H */
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index babddd05303796d689a64f0f5a890066b43170ac..d75dd9b59a5c35b76919db760645464f604517f5 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -923,6 +923,11 @@ struct fuse_conn {
> /** IDR for backing files ids */
> struct idr backing_files_map;
> #endif
> +
> +#ifdef CONFIG_FUSE_IO_URING
> + /** uring connection information*/
> + struct fuse_ring *ring;
> +#endif
> };
>
> /*
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 3ce4f4e81d09e867c3a7db7b1dbb819f88ed34ef..e4f9bbacfc1bc6f51d5d01b4c47b42cc159ed783 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -7,6 +7,7 @@
> */
>
> #include "fuse_i.h"
> +#include "dev_uring_i.h"
>
> #include <linux/pagemap.h>
> #include <linux/slab.h>
> @@ -992,6 +993,8 @@ static void delayed_release(struct rcu_head *p)
> {
> struct fuse_conn *fc = container_of(p, struct fuse_conn, rcu);
>
> + fuse_uring_destruct(fc);
> +
> put_user_ns(fc->user_ns);
> fc->release(fc);
> }
> @@ -1446,6 +1449,13 @@ void fuse_send_init(struct fuse_mount *fm)
> if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
> flags |= FUSE_PASSTHROUGH;
>
> + /*
> + * This is just an information flag for fuse server. No need to check
> + * the reply - server is either sending IORING_OP_URING_CMD or not.
> + */
> + if (fuse_uring_enabled())
> + flags |= FUSE_OVER_IO_URING;
> +
> ia->in.flags = flags;
> ia->in.flags2 = flags >> 32;
>
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index f1e99458e29e4fdce5273bc3def242342f207ebd..5e0eb41d967e9de5951673de4405a3ed22cdd8e2 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -220,6 +220,15 @@
> *
> * 7.41
> * - add FUSE_ALLOW_IDMAP
> + * 7.42
> + * - Add FUSE_OVER_IO_URING and all other io-uring related flags and data
> + * structures:
> + * - struct fuse_uring_ent_in_out
> + * - struct fuse_uring_req_header
> + * - struct fuse_uring_cmd_req
> + * - FUSE_URING_IN_OUT_HEADER_SZ
> + * - FUSE_URING_OP_IN_OUT_SZ
> + * - enum fuse_uring_cmd
> */
>
> #ifndef _LINUX_FUSE_H
> @@ -255,7 +264,7 @@
> #define FUSE_KERNEL_VERSION 7
>
> /** Minor version number of this interface */
> -#define FUSE_KERNEL_MINOR_VERSION 41
> +#define FUSE_KERNEL_MINOR_VERSION 42
>
> /** The node ID of the root inode */
> #define FUSE_ROOT_ID 1
> @@ -425,6 +434,7 @@ struct fuse_file_lock {
> * FUSE_HAS_RESEND: kernel supports resending pending requests, and the high bit
> * of the request ID indicates resend requests
> * FUSE_ALLOW_IDMAP: allow creation of idmapped mounts
> + * FUSE_OVER_IO_URING: Indicate that client supports io-uring
> */
> #define FUSE_ASYNC_READ (1 << 0)
> #define FUSE_POSIX_LOCKS (1 << 1)
> @@ -471,6 +481,7 @@ struct fuse_file_lock {
> /* Obsolete alias for FUSE_DIRECT_IO_ALLOW_MMAP */
> #define FUSE_DIRECT_IO_RELAX FUSE_DIRECT_IO_ALLOW_MMAP
> #define FUSE_ALLOW_IDMAP (1ULL << 40)
> +#define FUSE_OVER_IO_URING (1ULL << 41)
>
> /**
> * CUSE INIT request/reply flags
> @@ -1206,4 +1217,67 @@ struct fuse_supp_groups {
> uint32_t groups[];
> };
>
> +/**
> + * Size of the ring buffer header
> + */
> +#define FUSE_URING_IN_OUT_HEADER_SZ 128
> +#define FUSE_URING_OP_IN_OUT_SZ 128
> +
> +/* Used as part of the fuse_uring_req_header */
> +struct fuse_uring_ent_in_out {
> + uint64_t flags;
> +
> + /*
> + * commit ID to be used in a reply to a ring request (see also
> + * struct fuse_uring_cmd_req)
> + */
> + uint64_t commit_id;
> +
> + /* size of user payload buffer */
> + uint32_t payload_sz;
> + uint32_t padding;
> +
> + uint64_t reserved;
> +};
> +
> +/**
> + * Header for all fuse-io-uring requests
> + */
> +struct fuse_uring_req_header {
> + /* struct fuse_in_header / struct fuse_out_header */
> + char in_out[FUSE_URING_IN_OUT_HEADER_SZ];
> +
> + /* per op code header */
> + char op_in[FUSE_URING_OP_IN_OUT_SZ];
> +
> + struct fuse_uring_ent_in_out ring_ent_in_out;
> +};
> +
> +/**
> + * sqe commands to the kernel
> + */
> +enum fuse_uring_cmd {
> + FUSE_IO_URING_CMD_INVALID = 0,
> +
> + /* register the request buffer and fetch a fuse request */
> + FUSE_IO_URING_CMD_REGISTER = 1,
> +
> + /* commit fuse request result and fetch next request */
> + FUSE_IO_URING_CMD_COMMIT_AND_FETCH = 2,
> +};
> +
> +/**
> + * In the 80B command area of the SQE.
> + */
> +struct fuse_uring_cmd_req {
> + uint64_t flags;
> +
> + /* entry identifier for commits */
> + uint64_t commit_id;
> +
> + /* queue the command is for (queue index) */
> + uint16_t qid;
> + uint8_t padding[6];
> +};
> +
> #endif /* _LINUX_FUSE_H */
>
> --
> 2.43.0
>