From 8bc72d6c20c5e38783c4956c4d9fde9b3ee9140c Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Wed, 28 Feb 2024 11:30:20 -0500
Subject: ioq: Probe for supported io_uring operations

---
 src/ioq.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 67 insertions(+), 18 deletions(-)

diff --git a/src/ioq.c b/src/ioq.c
index 74e2587..f71ee6e 100644
--- a/src/ioq.c
+++ b/src/ioq.c
@@ -458,6 +458,17 @@ static void ioq_batch_push(struct ioqq *ioqq, struct ioq_batch *batch, struct io
 /** Sentinel stop command. */
 static struct ioq_ent IOQ_STOP;
 
+#if BFS_USE_LIBURING
+/**
+ * Supported io_uring operations.
+ */
+enum ioq_ring_ops {
+	IOQ_RING_OPENAT = 1 << 0,
+	IOQ_RING_CLOSE  = 1 << 1,
+	IOQ_RING_STATX  = 1 << 2,
+};
+#endif
+
 /** I/O queue thread-specific data. */
 struct ioq_thread {
 	/** The thread handle. */
@@ -470,6 +481,8 @@ struct ioq_thread {
 	struct io_uring ring;
 	/** Any error that occurred initializing the ring. */
 	int ring_err;
+	/** Bitmask of supported io_uring operations. */
+	enum ioq_ring_ops ring_ops;
 #endif
 };
 
@@ -553,6 +566,8 @@ struct ioq_ring_state {
 	struct ioq *ioq;
 	/** The io_uring. */
 	struct io_uring *ring;
+	/** Supported io_uring operations. */
+	enum ioq_ring_ops ops;
 	/** Number of prepped, unsubmitted SQEs. */
 	size_t prepped;
 	/** Number of submitted, unreaped SQEs. */
@@ -564,40 +579,48 @@ struct ioq_ring_state {
 };
 
 /** Dispatch a single request asynchronously. */
-static struct io_uring_sqe *ioq_dispatch_async(struct io_uring *ring, struct ioq_ent *ent) {
+static struct io_uring_sqe *ioq_dispatch_async(struct ioq_ring_state *state, struct ioq_ent *ent) {
+	struct io_uring *ring = state->ring;
+	enum ioq_ring_ops ops = state->ops;
 	struct io_uring_sqe *sqe = NULL;
 
 	switch (ent->op) {
-		case IOQ_CLOSE:
+	case IOQ_CLOSE:
+		if (ops & IOQ_RING_CLOSE) {
 			sqe = io_uring_get_sqe(ring);
 			io_uring_prep_close(sqe, ent->close.fd);
-			return sqe;
+		}
+		return sqe;
 
-		case IOQ_OPENDIR: {
+	case IOQ_OPENDIR:
+		if (ops & IOQ_RING_OPENAT) {
 			sqe = io_uring_get_sqe(ring);
 			struct ioq_opendir *args = &ent->opendir;
 			int flags = O_RDONLY | O_CLOEXEC | O_DIRECTORY;
 			io_uring_prep_openat(sqe, args->dfd, args->path, flags, 0);
-			return sqe;
 		}
+		return sqe;
 
-		case IOQ_CLOSEDIR:
+	case IOQ_CLOSEDIR:
 #if BFS_USE_UNWRAPDIR
+		if (ops & IOQ_RING_CLOSE) {
 			sqe = io_uring_get_sqe(ring);
 			io_uring_prep_close(sqe, bfs_unwrapdir(ent->closedir.dir));
+		}
 #endif
-			return sqe;
+		return sqe;
 
-		case IOQ_STAT: {
+	case IOQ_STAT:
 #if BFS_USE_STATX
+		if (ops & IOQ_RING_STATX) {
 			sqe = io_uring_get_sqe(ring);
 			struct ioq_stat *args = &ent->stat;
 			int flags = bfs_statx_flags(args->flags);
 			unsigned int mask = STATX_BASIC_STATS | STATX_BTIME;
 			io_uring_prep_statx(sqe, args->dfd, args->path, flags, mask, args->xbuf);
-#endif
-			return sqe;
 		}
+#endif
+		return sqe;
 	}
 
 	bfs_bug("Unknown ioq_op %d", (int)ent->op);
@@ -617,7 +640,7 @@ static void ioq_prep_sqe(struct ioq_ring_state *state, struct ioq_ent *ent) {
 		return;
 	}
 
-	struct io_uring_sqe *sqe = ioq_dispatch_async(state->ring, ent);
+	struct io_uring_sqe *sqe = ioq_dispatch_async(state, ent);
 	if (sqe) {
 		io_uring_sqe_set_data(sqe, ent);
 		++state->prepped;
@@ -743,6 +766,7 @@ static void ioq_ring_work(struct ioq_thread *thread) {
 	struct ioq_ring_state state = {
 		.ioq = thread->parent,
 		.ring = &thread->ring,
+		.ops = thread->ring_ops,
 	};
 
 	while (ioq_ring_prep(&state)) {
@@ -824,14 +848,39 @@ static int ioq_ring_init(struct ioq *ioq, struct ioq_thread *thread) {
 		return -1;
 	}
 
-	if (!prev) {
-		// Limit the number of io_uring workers
-		unsigned int values[] = {
-			ioq->nthreads, // [IO_WQ_BOUND]
-			0,             // [IO_WQ_UNBOUND]
-		};
-		io_uring_register_iowq_max_workers(&thread->ring, values);
+	if (prev) {
+		// Initial setup already complete
+		return 0;
+	}
+
+	// Check for supported operations
+	struct io_uring_probe *probe = io_uring_get_probe_ring(&thread->ring);
+	if (probe) {
+		if (io_uring_opcode_supported(probe, IORING_OP_OPENAT)) {
+			thread->ring_ops |= IOQ_RING_OPENAT;
+		}
+		if (io_uring_opcode_supported(probe, IORING_OP_CLOSE)) {
+			thread->ring_ops |= IOQ_RING_CLOSE;
+		}
+#if BFS_USE_STATX
+		if (io_uring_opcode_supported(probe, IORING_OP_STATX)) {
+			thread->ring_ops |= IOQ_RING_STATX;
+		}
+#endif
+		io_uring_free_probe(probe);
 	}
+	if (!thread->ring_ops) {
+		io_uring_queue_exit(&thread->ring);
+		thread->ring_err = ENOTSUP;
+		return -1;
+	}
+
+	// Limit the number of io_uring workers
+	unsigned int values[] = {
+		ioq->nthreads, // [IO_WQ_BOUND]
+		0,             // [IO_WQ_UNBOUND]
+	};
+	io_uring_register_iowq_max_workers(&thread->ring, values);
 #endif
 
 	return 0;
-- 
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