8 files changed, 630 insertions, 3 deletions

diff --git a/lib/fuse_i.h b/lib/fuse_i.h
index 89a5c6f..b643e90 100644
--- a/lib/fuse_i.h
+++ b/lib/fuse_i.h
@@ -6,6 +6,9 @@
   See the file COPYING.LIB
 */
 
+#ifndef LIB_FUSE_I_H_
+#define LIB_FUSE_I_H_
+
 #include "fuse.h"
 #include "fuse_lowlevel.h"
 #include "util.h"
@@ -24,6 +27,7 @@
 })
 
 struct mount_opts;
+struct fuse_ring_pool;
 
 struct fuse_req {
 	struct fuse_session *se;
@@ -34,6 +38,7 @@ struct fuse_req {
 	struct fuse_chan *ch;
 	int interrupted;
 	unsigned int ioctl_64bit : 1;
+	unsigned int is_uring : 1;
 	union {
 		struct {
 			uint64_t unique;
@@ -55,6 +60,11 @@ struct fuse_notify_req {
 	struct fuse_notify_req *prev;
 };
 
+struct fuse_session_uring {
+	unsigned int q_depth;
+	struct fuse_ring_pool *pool;
+};
+
 struct fuse_session {
 	char *mountpoint;
 	int fd;
@@ -79,7 +89,8 @@ struct fuse_session {
 	_Atomic size_t bufsize;
 	int error;
 
-	/* This is useful if any kind of ABI incompatibility is found at
+	/*
+	 * This is useful if any kind of ABI incompatibility is found at
 	 * a later version, to 'fix' it at run time.
 	 */
 	struct libfuse_version version;
@@ -91,6 +102,9 @@ struct fuse_session {
 
 	/* true if reading requests from /dev/fuse are handled internally */
 	bool buf_reallocable;
+
+	/* io_uring */
+	struct fuse_session_uring uring;
 };
 
 struct fuse_chan {
@@ -269,3 +283,5 @@ static inline int convert_to_conn_want_ext(struct fuse_conn_info *conn,
 
 	return 0;
 }
+
+#endif /* LIB_FUSE_I_H_*/
diff --git a/lib/fuse_loop.c b/lib/fuse_loop.c
index 410f43f..a27111c 100644
--- a/lib/fuse_loop.c
+++ b/lib/fuse_loop.c
@@ -11,7 +11,7 @@
 #include "fuse_config.h"
 #include "fuse_lowlevel.h"
 #include "fuse_i.h"
-
+#include "fuse_uring_i.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
@@ -41,6 +41,8 @@ int fuse_session_loop(struct fuse_session *se)
 		res = 0;
 	if(se->error != 0)
 		res = se->error;
-	fuse_session_reset(se);
+
+	if (se->uring.pool)
+		fuse_uring_stop(se);
 	return res;
 }
diff --git a/lib/fuse_uring.c b/lib/fuse_uring.c
new file mode 100644
index 0000000..ce56716
--- /dev/null
+++ b/lib/fuse_uring.c
@@ -0,0 +1,548 @@
+/*
+ * FUSE: Filesystem in Userspace
+ * Copyright (C) 2025  Bernd Schubert <bschubert@ddn.com>
+ *
+ * Implementation of (most of) the low-level FUSE API. The session loop
+ * functions are implemented in separate files.
+ *
+ * This program can be distributed under the terms of the GNU LGPLv2.
+ * See the file COPYING.LIB
+ */
+
+#define _GNU_SOURCE
+
+#include "fuse_i.h"
+#include "fuse_kernel.h"
+#include "fuse_uring_i.h"
+
+#include <stdlib.h>
+#include <liburing.h>
+#include <sys/sysinfo.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+#include <unistd.h>
+#include <numa.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <linux/sched.h>
+#include <poll.h>
+#include <sys/eventfd.h>
+
+/* Size of command data area in SQE when IORING_SETUP_SQE128 is used */
+#define FUSE_URING_MAX_SQE128_CMD_DATA 80
+
+struct fuse_ring_ent {
+	struct fuse_ring_queue *ring_queue; /* back pointer */
+	struct fuse_req req;
+
+	struct fuse_uring_req_header *req_header;
+	void *op_payload;
+	size_t req_payload_sz;
+
+	/* commit id of a fuse request */
+	uint64_t req_commit_id;
+
+	/* header and payload */
+	struct iovec iov[2];
+};
+
+struct fuse_ring_queue {
+	/* back pointer */
+	struct fuse_ring_pool *ring_pool;
+	int qid;
+	int numa_node;
+	pthread_t tid;
+	int eventfd;
+	size_t req_header_sz;
+	struct io_uring ring;
+
+	/* size depends on queue depth */
+	struct fuse_ring_ent ent[];
+};
+
+/**
+ * Main fuse_ring structure, holds all fuse-ring data
+ */
+struct fuse_ring_pool {
+	struct fuse_session *se;
+
+	/* number of queues */
+	size_t nr_queues;
+
+	/* number of per queue entries */
+	size_t queue_depth;
+
+	/* max payload size for fuse requests*/
+	size_t max_req_payload_sz;
+
+	/* size of a single queue */
+	size_t queue_mem_size;
+
+	/* pointer to the first queue */
+	struct fuse_ring_queue *queues;
+};
+
+static size_t
+fuse_ring_queue_size(const size_t q_depth)
+{
+	const size_t req_size = sizeof(struct fuse_ring_ent) * q_depth;
+
+	return sizeof(struct fuse_ring_queue) + req_size;
+}
+
+static struct fuse_ring_queue *
+fuse_uring_get_queue(struct fuse_ring_pool *fuse_ring, int qid)
+{
+	void *ptr =
+		((char *)fuse_ring->queues) + (qid * fuse_ring->queue_mem_size);
+
+	return ptr;
+}
+
+/**
+ * return a pointer to the 80B area
+ */
+static void *fuse_uring_get_sqe_cmd(struct io_uring_sqe *sqe)
+{
+	return (void *)&sqe->cmd[0];
+}
+
+static void fuse_uring_sqe_set_req_data(struct fuse_uring_cmd_req *req,
+					const unsigned int qid,
+					const unsigned int commit_id)
+{
+	req->qid = qid;
+	req->commit_id = commit_id;
+	req->flags = 0;
+}
+
+static void
+fuse_uring_sqe_prepare(struct io_uring_sqe *sqe, struct fuse_ring_ent *req,
+		       __u32 cmd_op)
+{
+	/* These fields should be written once, never change */
+	sqe->opcode = IORING_OP_URING_CMD;
+
+	/*
+	 * IOSQE_FIXED_FILE: fd is the index to the fd *array*
+	 * given to io_uring_register_files()
+	 */
+	sqe->flags = IOSQE_FIXED_FILE;
+	sqe->fd = 0;
+
+	sqe->rw_flags = 0;
+	sqe->ioprio = 0;
+	sqe->off = 0;
+
+	io_uring_sqe_set_data(sqe, req);
+
+	sqe->cmd_op = cmd_op;
+	sqe->__pad1 = 0;
+}
+
+static int fuse_queue_setup_io_uring(struct io_uring *ring, size_t qid,
+				     size_t depth, int fd, int evfd)
+{
+	int rc;
+	struct io_uring_params params = {0};
+	int files[2] = { fd, evfd };
+
+	depth += 1; /* for the eventfd poll SQE */
+
+	params.flags = IORING_SETUP_SQE128;
+
+	/* Avoid cq overflow */
+	params.flags |= IORING_SETUP_CQSIZE;
+	params.cq_entries = depth * 2;
+
+	/* These flags should help to increase performance, but actually
+	 * make it a bit slower - reason should get investigated.
+	 */
+	if (0) {
+		/* Has the main slow down effect */
+		params.flags |= IORING_SETUP_SINGLE_ISSUER;
+
+		// params.flags |= IORING_SETUP_DEFER_TASKRUN;
+		params.flags |= IORING_SETUP_TASKRUN_FLAG;
+
+		/* Second main effect to make it slower */
+		params.flags |= IORING_SETUP_COOP_TASKRUN;
+	}
+
+	rc = io_uring_queue_init_params(depth, ring, &params);
+	if (rc != 0) {
+		fuse_log(FUSE_LOG_ERR, "Failed to setup qid %zu: %d (%s)\n",
+			 qid, rc, strerror(-rc));
+		return rc;
+	}
+
+	rc = io_uring_register_files(ring, files, 1);
+	if (rc != 0) {
+		rc = -errno;
+		fuse_log(FUSE_LOG_ERR,
+			 "Failed to register files for ring idx %zu: %s",
+			 qid, strerror(errno));
+		return rc;
+	}
+
+	return 0;
+}
+
+static void fuse_session_destruct_uring(struct fuse_ring_pool *fuse_ring)
+{
+	for (size_t qid = 0; qid < fuse_ring->nr_queues; qid++) {
+		struct fuse_ring_queue *queue =
+			fuse_uring_get_queue(fuse_ring, qid);
+
+		if (queue->tid != 0) {
+			int value = 1;
+
+			write(queue->eventfd, &value, sizeof(value));
+			pthread_join(queue->tid, NULL);
+			queue->tid = 0;
+		}
+
+		if (queue->eventfd >= 0) {
+			close(queue->eventfd);
+			queue->eventfd = -1;
+		}
+
+		if (queue->ring.ring_fd != -1)
+			io_uring_queue_exit(&queue->ring);
+
+		for (size_t idx = 0; idx < fuse_ring->queue_depth; idx++) {
+			struct fuse_ring_ent *ent = &queue->ent[idx];
+
+			numa_free(ent->op_payload, ent->req_payload_sz);
+			numa_free(ent->req_header, queue->req_header_sz);
+		}
+	}
+
+	free(fuse_ring->queues);
+	free(fuse_ring);
+}
+
+static int fuse_uring_prepare_fetch_sqes(struct fuse_ring_queue *queue)
+{
+	struct fuse_ring_pool *ring_pool = queue->ring_pool;
+	unsigned int sq_ready;
+	struct io_uring_sqe *sqe;
+
+	for (size_t idx = 0; idx < ring_pool->queue_depth; idx++) {
+		struct fuse_ring_ent *ent = &queue->ent[idx];
+
+		sqe = io_uring_get_sqe(&queue->ring);
+		if (sqe == NULL) {
+			/* All SQEs are idle here - no good reason this
+			 * could fail
+			 */
+
+			fuse_log(FUSE_LOG_ERR, "Failed to get all ring SQEs");
+			return -EIO;
+		}
+
+		fuse_uring_sqe_prepare(sqe, ent, FUSE_IO_URING_CMD_REGISTER);
+
+		/* only needed for fetch */
+		ent->iov[0].iov_base = ent->req_header;
+		ent->iov[0].iov_len = queue->req_header_sz;
+
+		ent->iov[1].iov_base = ent->op_payload;
+		ent->iov[1].iov_len = ent->req_payload_sz;
+
+		sqe->addr = (uint64_t)(ent->iov);
+		sqe->len = 2;
+
+		/* this is a fetch, kernel does not read commit id */
+		fuse_uring_sqe_set_req_data(fuse_uring_get_sqe_cmd(sqe),
+					    queue->qid, 0);
+	}
+
+	sq_ready = io_uring_sq_ready(&queue->ring);
+	if (sq_ready != ring_pool->queue_depth) {
+		fuse_log(FUSE_LOG_ERR,
+			 "SQE ready mismatch, expected %d got %d\n",
+			 ring_pool->queue_depth, sq_ready);
+		return -EINVAL;
+	}
+
+	// Add the poll SQE for the eventfd to wake up on teardown
+	sqe = io_uring_get_sqe(&queue->ring);
+	if (sqe == NULL) {
+		fuse_log(FUSE_LOG_ERR, "Failed to get eventfd SQE");
+		return -EIO;
+	}
+
+	io_uring_prep_poll_add(sqe, queue->eventfd, POLLIN);
+	io_uring_sqe_set_data(sqe, (void *)(uintptr_t)queue->eventfd);
+
+	io_uring_submit(&queue->ring);
+
+	return 0;
+}
+
+static struct fuse_ring_pool *fuse_create_ring(struct fuse_session *se)
+{
+	struct fuse_ring_pool *fuse_ring = NULL;
+	const size_t nr_queues = get_nprocs_conf();
+	size_t payload_sz = se->bufsize - FUSE_BUFFER_HEADER_SIZE;
+	size_t queue_sz;
+
+	if (se->debug)
+		fuse_log(FUSE_LOG_DEBUG, "starting io-uring q-depth=%d\n",
+			 se->uring.q_depth);
+
+	fuse_ring = calloc(1, sizeof(*fuse_ring));
+	if (fuse_ring == NULL) {
+		fuse_log(FUSE_LOG_ERR, "Allocating the ring failed\n");
+		goto err;
+	}
+
+	queue_sz = fuse_ring_queue_size(se->uring.q_depth);
+	fuse_ring->queues = calloc(1, queue_sz * nr_queues);
+	if (fuse_ring->queues == NULL) {
+		fuse_log(FUSE_LOG_ERR, "Allocating the queues failed\n");
+		goto err;
+	}
+
+	fuse_ring->se = se;
+	fuse_ring->nr_queues = nr_queues;
+	fuse_ring->queue_depth = se->uring.q_depth;
+	fuse_ring->max_req_payload_sz = payload_sz;
+	fuse_ring->queue_mem_size = queue_sz;
+
+	/*
+	 * very basic queue initialization, that cannot fail and will
+	 * allow easy cleanup if something (like mmap) fails in the middle
+	 * below
+	 */
+	for (size_t qid = 0; qid < nr_queues; qid++) {
+		struct fuse_ring_queue *queue =
+			fuse_uring_get_queue(fuse_ring, qid);
+
+		queue->ring.ring_fd = -1;
+		queue->numa_node = numa_node_of_cpu(qid);
+		queue->qid = qid;
+		queue->ring_pool = fuse_ring;
+	}
+
+	return fuse_ring;
+
+err:
+	if (fuse_ring)
+		fuse_session_destruct_uring(fuse_ring);
+
+	return NULL;
+}
+
+/* stub function */
+static int fuse_uring_queue_handle_cqes(struct fuse_ring_queue *queue)
+{
+	(void)queue;
+
+	return 0;
+}
+
+/**
+ * In per-core-queue configuration we have thread per core - the thread
+ * to that core
+ */
+static void fuse_uring_set_thread_core(int qid)
+{
+	cpu_set_t mask;
+	int rc;
+
+	CPU_ZERO(&mask);
+	CPU_SET(qid, &mask);
+	rc = sched_setaffinity(0, sizeof(cpu_set_t), &mask);
+	if (rc != 0)
+		fuse_log(FUSE_LOG_ERR, "Failed to bind qid=%d to its core: %s\n",
+			 qid, strerror(errno));
+
+	if (0) {
+		const int policy = SCHED_IDLE;
+		const struct sched_param param = {
+			.sched_priority = sched_get_priority_min(policy),
+		};
+
+		/* Set the lowest possible priority, so that the application
+		 * submitting requests is not moved away from the current core.
+		 */
+		rc = sched_setscheduler(0, policy, &param);
+		if (rc != 0)
+			fuse_log(FUSE_LOG_ERR, "Failed to set scheduler: %s\n",
+				strerror(errno));
+	}
+}
+
+/*
+ * @return negative error code or io-uring file descriptor
+ */
+static int fuse_uring_init_queue(struct fuse_ring_queue *queue)
+{
+	struct fuse_ring_pool *ring = queue->ring_pool;
+	struct fuse_session *se = ring->se;
+	int res;
+	size_t page_sz = sysconf(_SC_PAGESIZE);
+
+	queue->eventfd = eventfd(0, EFD_CLOEXEC);
+	if (queue->eventfd < 0) {
+		res = -errno;
+		fuse_log(FUSE_LOG_ERR,
+			 "Failed to create eventfd for qid %d: %s\n",
+			 queue->qid, strerror(errno));
+		return res;
+	}
+
+	res = fuse_queue_setup_io_uring(&queue->ring, queue->qid,
+					ring->queue_depth, se->fd,
+					queue->eventfd);
+	if (res != 0) {
+		fuse_log(FUSE_LOG_ERR, "qid=%d io_uring init failed\n",
+			 queue->qid);
+		goto err;
+	}
+
+	queue->req_header_sz = ROUND_UP(sizeof(struct fuse_ring_ent),
+				       page_sz);
+
+	for (size_t idx = 0; idx < ring->queue_depth; idx++) {
+		struct fuse_ring_ent *ring_ent = &queue->ent[idx];
+		struct fuse_req *req = &ring_ent->req;
+
+		ring_ent->ring_queue = queue;
+
+		/*
+		 * Also allocate the header to have it page aligned, which
+		 * is a requirement for page pinning
+		 */
+		ring_ent->req_header =
+			numa_alloc_local(queue->req_header_sz);
+		ring_ent->req_payload_sz = ring->max_req_payload_sz;
+
+		ring_ent->op_payload =
+			numa_alloc_local(ring_ent->req_payload_sz);
+
+		req->se = se;
+		pthread_mutex_init(&req->lock, NULL);
+		req->is_uring = true;
+		req->ref_cnt = 1;
+	}
+
+	res = fuse_uring_prepare_fetch_sqes(queue);
+	if (res != 0) {
+		fuse_log(
+			FUSE_LOG_ERR,
+			"Grave fuse-uring error on preparing SQEs, aborting\n");
+		se->error = -EIO;
+		fuse_session_exit(se);
+	}
+
+	return queue->ring.ring_fd;
+
+err:
+	close(queue->eventfd);
+	return res;
+}
+
+static void *fuse_uring_thread(void *arg)
+{
+	struct fuse_ring_queue *queue = arg;
+	struct fuse_ring_pool *ring_pool = queue->ring_pool;
+	struct fuse_session *se = ring_pool->se;
+	int err;
+	char thread_name[16] = { 0 };
+
+	snprintf(thread_name, 16, "fuse-ring-%d", queue->qid);
+	thread_name[15] = '\0';
+	fuse_set_thread_name(pthread_self(), thread_name);
+
+	fuse_uring_set_thread_core(queue->qid);
+
+	err = fuse_uring_init_queue(queue);
+	if (err < 0) {
+		fuse_log(FUSE_LOG_ERR, "qid=%d queue setup failed\n",
+			 queue->qid);
+		goto err;
+	}
+
+	/* Not using fuse_session_exited(se), as that cannot be inlined */
+	while (!atomic_load_explicit(&se->mt_exited, memory_order_relaxed)) {
+		io_uring_submit_and_wait(&queue->ring, 1);
+
+		err = fuse_uring_queue_handle_cqes(queue);
+		if (err < 0) {
+			/*
+			 * fuse-over-io-uring is not supported, operation can
+			 * continue over /dev/fuse
+			 */
+			if (err == -EOPNOTSUPP)
+				goto ret;
+			goto err;
+		}
+	}
+
+	return NULL;
+
+err:
+	fuse_session_exit(se);
+ret:
+	return NULL;
+}
+
+static int fuse_uring_start_ring_threads(struct fuse_ring_pool *ring)
+{
+	int rc = 0;
+
+	for (size_t qid = 0; qid < ring->nr_queues; qid++) {
+		struct fuse_ring_queue *queue = fuse_uring_get_queue(ring, qid);
+
+		rc = pthread_create(&queue->tid, NULL, fuse_uring_thread, queue);
+		if (rc != 0)
+			break;
+	}
+
+	return rc;
+}
+
+static int fuse_uring_sanity_check(void)
+{
+	_Static_assert(sizeof(struct fuse_uring_cmd_req) <=
+		       FUSE_URING_MAX_SQE128_CMD_DATA,
+		       "SQE128_CMD_DATA has 80B cmd data");
+
+	return 0;
+}
+
+int fuse_uring_start(struct fuse_session *se)
+{
+	int err = 0;
+	struct fuse_ring_pool *fuse_ring;
+
+	fuse_uring_sanity_check();
+
+	fuse_ring = fuse_create_ring(se);
+	if (fuse_ring == NULL) {
+		err = -EADDRNOTAVAIL;
+		goto out;
+	}
+
+	se->uring.pool = fuse_ring;
+
+	err = fuse_uring_start_ring_threads(fuse_ring);
+out:
+	return err;
+}
+
+int fuse_uring_stop(struct fuse_session *se)
+{
+	struct fuse_ring_pool *ring = se->uring.pool;
+
+	if (ring == NULL)
+		return 0;
+
+	fuse_session_destruct_uring(ring);
+
+	return 0;
+}
diff --git a/lib/fuse_uring_i.h b/lib/fuse_uring_i.h
new file mode 100644
index 0000000..fefb8a0
--- /dev/null
+++ b/lib/fuse_uring_i.h
@@ -0,0 +1,18 @@
+/*
+ * FUSE: Filesystem in Userspace
+ * Copyright (C) 2025       Bernd Schubert <bschubert@ddn.com>
+ * This program can be distributed under the terms of the GNU LGPLv2.
+ * See the file COPYING.LIB
+ */
+
+#ifndef FUSE_URING_I_H_
+#define FUSE_URING_I_H_
+
+#include "fuse_lowlevel.h"
+
+struct fuse_in_header;
+
+int fuse_uring_start(struct fuse_session *se);
+int fuse_uring_stop(struct fuse_session *se);
+
+#endif // FUSE_URING_I_H_
diff --git a/lib/meson.build b/lib/meson.build
index 6a52d06..fcd9574 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -19,6 +19,14 @@ if private_cfg.get('HAVE_ICONV')
    endif
 endif
 
+if private_cfg.get('HAVE_URING', false)
+  libfuse_sources += [ 'fuse_uring.c' ]
+  deps += [ dependency('liburing') ]
+  deps += [ dependency('numa') ]
+endif
+
+
+
 libdl = cc.find_library('dl', required: false)
 if libdl.found()
    deps += [ libdl ]
diff --git a/meson.build b/meson.build
index 3615a5a..b663109 100644
--- a/meson.build
+++ b/meson.build
@@ -132,6 +132,32 @@ private_cfg.set('HAVE_STRUCT_STAT_ST_ATIMESPEC',
 
 private_cfg.set('USDT_ENABLED', get_option('enable-usdt'))
 
+# Check for liburing with SQE128 support
+code = '''
+#include <liburing.h>
+#include <stdio.h>
+int main(void) {
+    struct io_uring ring;
+    int ret = io_uring_queue_init(1, &ring, 0);
+#ifndef IORING_SETUP_SQE128
+#error "No SQE128 support"
+#endif
+    return ret;
+}'''
+
+liburing = get_option('enable-io-uring') ? \
+    dependency('liburing', required: false) :\
+    dependency('', required: false)
+libnuma = dependency('numa', required: false)
+
+if liburing.found() and libnuma.found()
+   if cc.links(code,
+              name: 'liburing linking and SQE128 support',
+              dependencies: [liburing])
+      private_cfg.set('HAVE_URING', true)
+   endif
+endif
+
 #
 # Compiler configuration
 #
diff --git a/meson_options.txt b/meson_options.txt
index 957c5fc..c1f8fe6 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -24,3 +24,6 @@ option('disable-libc-symbol-version', type : 'boolean', value : false,
 
 option('enable-usdt', type : 'boolean', value : false,
        description: 'Enable user statically defined tracepoints for extra observability')
+
+option('enable-io-uring', type: 'boolean', value: true,
+       description: 'Enable fuse-over-io-uring support')
diff --git a/test/ci-build.sh b/test/ci-build.sh
index 40bb79e..86230bd 100755
--- a/test/ci-build.sh
+++ b/test/ci-build.sh
@@ -146,6 +146,12 @@ export CC=clang
 export CXX=clang++
 sanitized_build "-Ddisable-libc-symbol-version=true"
 
+# Sanitized build without fuse-io-uring
+export CC=clang
+export CXX=clang++
+sanitized_build "-Denable-io-uring=false"
+
+# Build without any sanitizer
 non_sanitized_build
 
 # Documentation.