[PATCH net-next v6 2/8] ptr_ring: add helper to check if consume created space

[Simon Schippers]

Add __ptr_ring_consume_created_space() to check whether the previous
__ptr_ring_consume() call successfully consumed an element and created
space in the ring buffer. This enables callers to conditionally notify
producers when space becomes available.

The function is only valid immediately after a single consume operation
and should not be used after calling __ptr_ring_consume_batched().

Co-developed-by: Tim Gebauer <tim.gebauer@xxxxxxxxxxxxxx>
Signed-off-by: Tim Gebauer <tim.gebauer@xxxxxxxxxxxxxx>
Co-developed by: Jon Kohler <jon@xxxxxxxxxxx>
Signed-off-by: Jon Kohler <jon@xxxxxxxxxxx>
Signed-off-by: Simon Schippers <simon.schippers@xxxxxxxxxxxxxx>
---
 include/linux/ptr_ring.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index da141cc8b075..76d6840b45a3 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -453,6 +453,23 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r,
 	return ret;
 }
 
+/*
+ * Check if the previous consume operation created space
+ *
+ * Returns true if the last call to __ptr_ring_consume() has created
+ * space in the ring buffer (i.e., an element was consumed).
+ *
+ * Note: This function is only valid immediately after a single call to
+ * __ptr_ring_consume(). If multiple calls to ptr_ring_consume*() have
+ * been made, this check must be performed after each call individually.
+ * Likewise, do not use this function after calling
+ * __ptr_ring_consume_batched().
+ */
+static inline bool __ptr_ring_consume_created_space(struct ptr_ring *r)
+{
+	return r->consumer_tail >= r->consumer_head;
+}
+
 /* Cast to structure type and call a function without discarding from FIFO.
  * Function must return a value.
  * Callers must take consumer_lock.
-- 
2.43.0