ioq: Use io_uring

Closes #65.

2 files changed, 288 insertions, 42 deletions

diff --git a/src/bftw.c b/src/bftw.c
index 5e5f4a5..902a3fa 100644
--- a/src/bftw.c
+++ b/src/bftw.c
@@ -470,21 +470,34 @@ static int bftw_state_init(struct bftw_state *state, const struct bftw_args *arg
 
 	state->error = 0;
 
-	if (args->nopenfd < 1) {
+	if (args->nopenfd < 2) {
 		errno = EMFILE;
 		return -1;
 	}
-	bftw_cache_init(&state->cache, args->nopenfd);
 
-	state->nthreads = args->nthreads;
-	if (state->nthreads > 0) {
-		state->ioq = ioq_create(4096, state->nthreads);
+	size_t nopenfd = args->nopenfd;
+	size_t qdepth = 4096;
+	size_t nthreads = args->nthreads;
+
+#if BFS_USE_LIBURING
+	// io_uring uses one fd per ring, ioq uses one ring per thread
+	if (nthreads >= nopenfd - 1) {
+		nthreads = nopenfd - 2;
+	}
+	nopenfd -= nthreads;
+#endif
+
+	bftw_cache_init(&state->cache, nopenfd);
+
+	if (nthreads > 0) {
+		state->ioq = ioq_create(qdepth, nthreads);
 		if (!state->ioq) {
 			return -1;
 		}
 	} else {
 		state->ioq = NULL;
 	}
+	state->nthreads = nthreads;
 
 	SLIST_INIT(&state->to_open);
 	SLIST_INIT(&state->to_read);
diff --git a/src/ioq.c b/src/ioq.c
index d3ba2de..04b9c0d 100644
--- a/src/ioq.c
+++ b/src/ioq.c
@@ -16,6 +16,10 @@
 #include <pthread.h>
 #include <stdlib.h>
 
+#if BFS_USE_LIBURING
+#  include <liburing.h>
+#endif
+
 /**
  * A monitor for an I/O queue slot.
  */
@@ -280,6 +284,21 @@ static struct ioq_ent *ioqq_trypop(struct ioqq *ioqq) {
 /** Sentinel stop command. */
 static struct ioq_ent IOQ_STOP;
 
+/** I/O queue thread-specific data. */
+struct ioq_thread {
+	/** The thread handle. */
+	pthread_t id;
+	/** Pointer back to the I/O queue. */
+	struct ioq *parent;
+
+#if BFS_USE_LIBURING
+	/** io_uring instance. */
+	struct io_uring ring;
+	/** Any error that occurred initializing the ring. */
+	int ring_err;
+#endif
+};
+
 struct ioq {
 	/** The depth of the queue. */
 	size_t depth;
@@ -299,60 +318,247 @@ struct ioq {
 	/** The number of background threads. */
 	size_t nthreads;
 	/** The background threads themselves. */
-	pthread_t threads[];
+	struct ioq_thread threads[];
 };
 
-/** Background thread entry point. */
-static void *ioq_work(void *ptr) {
-	struct ioq *ioq = ptr;
+/** Cancel a request if we need to. */
+static bool ioq_check_cancel(struct ioq *ioq, struct ioq_ent *ent) {
+	if (!load(&ioq->cancel, relaxed)) {
+		return false;
+	}
 
-	while (true) {
-		struct ioq_ent *ent = ioqq_pop(ioq->pending);
-		if (ent == &IOQ_STOP) {
-			break;
+	// Always close(), even if we're cancelled, just like a real EINTR
+	if (ent->op == IOQ_CLOSE || ent->op == IOQ_CLOSEDIR) {
+		return false;
+	}
+
+	ent->ret = -1;
+	ent->error = EINTR;
+	ioqq_push(ioq->ready, ent);
+	return true;
+}
+
+/** Handle a single request synchronously. */
+static void ioq_handle(struct ioq *ioq, struct ioq_ent *ent) {
+	int ret;
+
+	switch (ent->op) {
+	case IOQ_CLOSE:
+		ret = xclose(ent->close.fd);
+		break;
+
+	case IOQ_OPENDIR:
+		ret = bfs_opendir(ent->opendir.dir, ent->opendir.dfd, ent->opendir.path);
+		if (ret == 0) {
+			bfs_polldir(ent->opendir.dir);
 		}
+		break;
+
+	case IOQ_CLOSEDIR:
+		ret = bfs_closedir(ent->closedir.dir);
+		break;
+
+	default:
+		bfs_bug("Unknown ioq_op %d", (int)ent->op);
+		ret = -1;
+		errno = ENOSYS;
+		break;
+	}
+
+	ent->ret = ret;
+	ent->error = ret == 0 ? 0 : errno;
+
+	ioqq_push(ioq->ready, ent);
+}
 
-		bool cancel = load(&ioq->cancel, relaxed);
+#if BFS_USE_LIBURING
+/** io_uring worker state. */
+struct ioq_ring_state {
+	/** The I/O queue. */
+	struct ioq *ioq;
+	/** The io_uring. */
+	struct io_uring *ring;
+	/** The current ioq->pending slot. */
+	ioq_slot *slot;
+	/** Number of prepped, unsubmitted SQEs. */
+	size_t prepped;
+	/** Number of submitted, unreaped SQEs. */
+	size_t submitted;
+	/** Whether to stop the loop. */
+	bool stop;
+};
+
+/** Pop a request for ioq_ring_prep(). */
+static struct ioq_ent *ioq_ring_pop(struct ioq_ring_state *state) {
+	if (state->stop) {
+		return NULL;
+	}
+
+	// Advance to the next slot if necessary
+	struct ioq *ioq = state->ioq;
+	if (!state->slot) {
+		state->slot = ioqq_read(ioq->pending);
+	}
+
+	// Block if we have nothing else to do
+	bool block = !state->prepped && !state->submitted;
+	struct ioq_ent *ret = ioq_slot_pop(ioq->pending, state->slot, block);
+
+	if (ret) {
+		// Got an entry, move to the next slot next time
+		state->slot = NULL;
+	}
+
+	if (ret == &IOQ_STOP) {
+		state->stop = true;
+		ret = NULL;
+	}
+
+	return ret;
+}
 
-		ent->ret = -1;
+/** Prep a single SQE. */
+static void ioq_prep_sqe(struct io_uring_sqe *sqe, struct ioq_ent *ent) {
+	switch (ent->op) {
+	case IOQ_CLOSE:
+		io_uring_prep_close(sqe, ent->close.fd);
+		break;
+
+	case IOQ_OPENDIR:
+		io_uring_prep_openat(sqe, ent->opendir.dfd, ent->opendir.path, O_RDONLY | O_CLOEXEC | O_DIRECTORY, 0);
+		break;
+
+#if BFS_USE_UNWRAPDIR
+	case IOQ_CLOSEDIR:
+		io_uring_prep_close(sqe, bfs_unwrapdir(ent->closedir.dir));
+		break;
+#endif
+
+	default:
+		bfs_bug("Unknown ioq_op %d", (int)ent->op);
+		io_uring_prep_nop(sqe);
+		break;
+	}
 
-		switch (ent->op) {
-		case IOQ_CLOSE:
-			// Always close(), even if we're cancelled, just like a real EINTR
-			ent->ret = xclose(ent->close.fd);
+	io_uring_sqe_set_data(sqe, ent);
+}
+
+/** Prep a batch of SQEs. */
+static bool ioq_ring_prep(struct ioq_ring_state *state) {
+	struct ioq *ioq = state->ioq;
+	struct io_uring *ring = state->ring;
+
+	while (io_uring_sq_space_left(ring)) {
+		struct ioq_ent *ent = ioq_ring_pop(state);
+		if (!ent) {
 			break;
+		}
+
+		if (ioq_check_cancel(ioq, ent)) {
+			continue;
+		}
 
-		case IOQ_OPENDIR:
-			if (!cancel) {
-				struct ioq_opendir *args = &ent->opendir;
-				ent->ret = bfs_opendir(args->dir, args->dfd, args->path);
-				if (ent->ret == 0) {
-					bfs_polldir(args->dir);
-				}
+#if !BFS_USE_UNWRAPDIR
+		if (ent->op == IOQ_CLOSEDIR) {
+			ioq_handle(ioq, ent);
+			continue;
+		}
+#endif
+
+		struct io_uring_sqe *sqe = io_uring_get_sqe(ring);
+		ioq_prep_sqe(sqe, ent);
+		++state->prepped;
+	}
+
+	return state->prepped || state->submitted;
+}
+
+/** Reap a batch of SQEs. */
+static void ioq_ring_reap(struct ioq_ring_state *state) {
+	struct ioq *ioq = state->ioq;
+	struct io_uring *ring = state->ring;
+
+	while (state->prepped) {
+		int ret = io_uring_submit_and_wait(ring, 1);
+		if (ret > 0) {
+			state->prepped -= ret;
+			state->submitted += ret;
+		}
+	}
+
+	while (state->submitted) {
+		struct io_uring_cqe *cqe;
+		if (io_uring_wait_cqe(ring, &cqe) < 0) {
+			continue;
+		}
+
+		struct ioq_ent *ent = io_uring_cqe_get_data(cqe);
+		ent->ret = cqe->res >= 0 ? cqe->res : -1;
+		ent->error = cqe->res < 0 ? -cqe->res : 0;
+		io_uring_cqe_seen(ring, cqe);
+		--state->submitted;
+
+		if (ent->op == IOQ_OPENDIR && ent->ret >= 0) {
+			int fd = ent->ret;
+			if (ioq_check_cancel(ioq, ent)) {
+				xclose(fd);
+				continue;
 			}
-			break;
 
-		case IOQ_CLOSEDIR:
-			ent->ret = bfs_closedir(ent->closedir.dir);
-			break;
+			ent->ret = bfs_opendir(ent->opendir.dir, fd, NULL);
+			if (ent->ret == 0) {
+				// TODO: io_uring_prep_getdents()
+				bfs_polldir(ent->opendir.dir);
+			} else {
+				ent->error = errno;
+			}
+		}
+
+		ioqq_push(ioq->ready, ent);
+	}
+}
+
+/** io_uring worker loop. */
+static void ioq_ring_work(struct ioq_thread *thread) {
+	struct ioq_ring_state state = {
+		.ioq = thread->parent,
+		.ring = &thread->ring,
+	};
 
-		default:
-			bfs_bug("Unknown ioq_op %d", (int)ent->op);
-			errno = ENOSYS;
+	while (ioq_ring_prep(&state)) {
+		ioq_ring_reap(&state);
+	}
+}
+#endif
+
+/** Synchronous syscall loop. */
+static void ioq_sync_work(struct ioq_thread *thread) {
+	struct ioq *ioq = thread->parent;
+
+	while (true) {
+		struct ioq_ent *ent = ioqq_pop(ioq->pending);
+		if (ent == &IOQ_STOP) {
 			break;
 		}
 
-		if (cancel) {
-			ent->error = EINTR;
-		} else if (ent->ret < 0) {
-			ent->error = errno;
-		} else {
-			ent->error = 0;
+		if (!ioq_check_cancel(ioq, ent)) {
+			ioq_handle(ioq, ent);
 		}
+	}
+}
 
-		ioqq_push(ioq->ready, ent);
+/** Background thread entry point. */
+static void *ioq_work(void *ptr) {
+	struct ioq_thread *thread = ptr;
+
+#if BFS_USE_LIBURING
+	if (thread->ring_err == 0) {
+		ioq_ring_work(thread);
+		return NULL;
 	}
+#endif
 
+	ioq_sync_work(thread);
 	return NULL;
 }
 
@@ -376,7 +582,30 @@ struct ioq *ioq_create(size_t depth, size_t nthreads) {
 	}
 
 	for (size_t i = 0; i < nthreads; ++i) {
-		if (thread_create(&ioq->threads[i], NULL, ioq_work, ioq) != 0) {
+		struct ioq_thread *thread = &ioq->threads[i];
+		thread->parent = ioq;
+
+#if BFS_USE_LIBURING
+		struct ioq_thread *prev = i ? &ioq->threads[i - 1] : NULL;
+		if (prev && prev->ring_err) {
+			thread->ring_err = prev->ring_err;
+		} else {
+			// Share io-wq workers between rings
+			struct io_uring_params params = {0};
+			if (prev) {
+				params.flags |= IORING_SETUP_ATTACH_WQ;
+				params.wq_fd = prev->ring.ring_fd;
+			}
+
+			size_t entries = depth / nthreads;
+			if (entries < 16) {
+				entries = 16;
+			}
+			thread->ring_err = -io_uring_queue_init_params(entries, &thread->ring, &params);
+		}
+#endif
+
+		if (thread_create(&thread->id, NULL, ioq_work, thread) != 0) {
 			goto fail;
 		}
 		++ioq->nthreads;
@@ -496,7 +725,11 @@ void ioq_destroy(struct ioq *ioq) {
 	ioq_cancel(ioq);
 
 	for (size_t i = 0; i < ioq->nthreads; ++i) {
-		thread_join(ioq->threads[i], NULL);
+		struct ioq_thread *thread = &ioq->threads[i];
+		thread_join(thread->id, NULL);
+#if BFS_USE_LIBURING
+		io_uring_queue_exit(&thread->ring);
+#endif
 	}
 
 	ioqq_destroy(ioq->ready);