Subject: [RFC PATCH v2 05/21] uapi/misc: add shqueue.h for shared queues

From: Jonathan Lemon <[email-masked]>
Date: Mon, 27 Jul 2020 15:44:28 -0700

From: Jonathan Lemon <[email-masked]>

Shared queues between user and kernel use their own private structures
for accessing a shared data area, but they need to use the same queue
functions.

Have the kernel use the same UAPI file - this can be made private at
a later date if required.

Signed-off-by: Jonathan Lemon <[email-masked]>
---
 include/uapi/misc/shqueue.h | 200 ++++++++++++++++++++++++++++++++++++
 1 file changed, 200 insertions(+)
 create mode 100644 include/uapi/misc/shqueue.h

diff --git a/include/uapi/misc/shqueue.h b/include/uapi/misc/shqueue.h
new file mode 100644
index 000000000000..ff945942734c
--- /dev/null
+++ b/include/uapi/misc/shqueue.h
@@ -0,0 +1,200 @@
+#ifndef _UAPI_MISC_SHQUEUE_H
+#define _UAPI_MISC_SHQUEUE_H
+
+/* Placed under UAPI in order to avoid two identical copies between
+ * user and kernel space.
+ */
+
+/* user and kernel private copy - identical in order to share sq* fcns */
+struct shared_queue {
+	unsigned *prod;
+	unsigned *cons;
+	unsigned char *data;
+	unsigned elt_sz;
+	unsigned mask;
+	unsigned cached_prod;
+	unsigned cached_cons;
+	unsigned entries;
+
+	unsigned map_sz;
+	void *map_ptr;
+};
+
+/*
+ * see documenation in tools/include/linux/ring_buffer.h
+ * using  explicit smp_/_ONCE is an optimization over smp_{store|load}
+ */
+
+static inline void __sq_load_acquire_cons(struct shared_queue *q)
+{
+	/* Refresh the local tail pointer */
+	q->cached_cons = READ_ONCE(*q->cons);
+	/* A, matches D */
+}
+
+static inline void __sq_store_release_cons(struct shared_queue *q)
+{
+	smp_mb(); /* D, matches A */
+	WRITE_ONCE(*q->cons, q->cached_cons);
+}
+
+static inline void __sq_load_acquire_prod(struct shared_queue *q)
+{
+	/* Refresh the local pointer */
+	q->cached_prod = READ_ONCE(*q->prod);
+	smp_rmb(); /* C, matches B */
+}
+
+static inline void __sq_store_release_prod(struct shared_queue *q)
+{
+	smp_wmb(); /* B, matches C */
+	WRITE_ONCE(*q->prod, q->cached_prod);
+}
+
+static inline void sq_cons_refresh(struct shared_queue *q)
+{
+	__sq_store_release_cons(q);
+	__sq_load_acquire_prod(q);
+}
+
+static inline bool sq_is_empty(struct shared_queue *q)
+{
+	return READ_ONCE(*q->prod) == READ_ONCE(*q->cons);
+}
+
+static inline bool sq_cons_empty(struct shared_queue *q)
+{
+	return q->cached_prod == q->cached_cons;
+}
+
+static inline unsigned __sq_cons_ready(struct shared_queue *q)
+{
+	return q->cached_prod - q->cached_cons;
+}
+
+static inline unsigned sq_cons_ready(struct shared_queue *q)
+{
+	if (sq_cons_empty(q))
+		__sq_load_acquire_prod(q);
+
+	return __sq_cons_ready(q);
+}
+
+static inline bool sq_cons_avail(struct shared_queue *q, unsigned count)
+{
+	if (count <= __sq_cons_ready(q))
+		return true;
+	__sq_load_acquire_prod(q);
+	return count <= __sq_cons_ready(q);
+}
+
+static inline void *sq_get_ptr(struct shared_queue *q, unsigned idx)
+{
+	return q->data + (idx & q->mask) * q->elt_sz;
+}
+
+static inline void sq_cons_complete(struct shared_queue *q)
+{
+	__sq_store_release_cons(q);
+}
+
+static inline void *sq_cons_peek(struct shared_queue *q)
+{
+	if (sq_cons_empty(q)) {
+		sq_cons_refresh(q);
+		if (sq_cons_empty(q))
+			return NULL;
+	}
+	return sq_get_ptr(q, q->cached_cons);
+}
+
+static inline unsigned
+sq_peek_batch(struct shared_queue *q, void **ptr, unsigned count)
+{
+	unsigned i, idx, ready;
+
+	ready = sq_cons_ready(q);
+	if (!ready)
+		return 0;
+
+	count = count > ready ? ready : count;
+
+	idx = q->cached_cons;
+	for (i = 0; i < count; i++)
+		ptr[i] = sq_get_ptr(q, idx++);
+
+	q->cached_cons += count;
+
+	return count;
+}
+
+static inline unsigned
+sq_cons_batch(struct shared_queue *q, void **ptr, unsigned count)
+{
+	unsigned i, idx, ready;
+
+	ready = sq_cons_ready(q);
+	if (!ready)
+		return 0;
+
+	count = count > ready ? ready : count;
+
+	idx = q->cached_cons;
+	for (i = 0; i < count; i++)
+		ptr[i] = sq_get_ptr(q, idx++);
+
+	q->cached_cons += count;
+	sq_cons_complete(q);
+
+	return count;
+}
+
+static inline void sq_cons_advance(struct shared_queue *q)
+{
+	q->cached_cons++;
+}
+
+static inline unsigned __sq_prod_space(struct shared_queue *q)
+{
+	return q->entries - (q->cached_prod - q->cached_cons);
+}
+
+static inline unsigned sq_prod_space(struct shared_queue *q)
+{
+	unsigned space;
+
+	space = __sq_prod_space(q);
+	if (!space) {
+		__sq_load_acquire_cons(q);
+		space = __sq_prod_space(q);
+	}
+	return space;
+}
+
+static inline bool sq_prod_avail(struct shared_queue *q, unsigned count)
+{
+	if (count <= __sq_prod_space(q))
+		return true;
+	__sq_load_acquire_cons(q);
+	return count <= __sq_prod_space(q);
+}
+
+static inline void *sq_prod_get_ptr(struct shared_queue *q)
+{
+	return sq_get_ptr(q, q->cached_prod++);
+}
+
+static inline void *sq_prod_reserve(struct shared_queue *q)
+{
+	if (!sq_prod_space(q))
+		return NULL;
+
+	return sq_prod_get_ptr(q);
+}
+
+static inline void sq_prod_submit(struct shared_queue *q)
+{
+	__sq_store_release_prod(q);
+}
+
+#endif /* _UAPI_MISC_SHQUEUE_H */
-- 
2.24.1