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

Bernd Schubert
2025-01-20T01:29:22Z

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.

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);
+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.
+ */
+ 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;
+ 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