This proposed function checks whether __ptr_ring_zero_tail() was invoked within the last n calls to __ptr_ring_consume(), which indicates that new free space was created. Since __ptr_ring_zero_tail() moves the tail to the head - and no other function modifies either the head or the tail, aside from the wrap-around case described below - detecting such a movement is sufficient to detect the invocation of __ptr_ring_zero_tail().
The implementation detects this movement by checking whether the tail is at most n positions behind the head. If this condition holds, the shift of the tail to its current position must have occurred within the last n calls to __ptr_ring_consume(), indicating that __ptr_ring_zero_tail() was invoked and that new free space was created. This logic also correctly handles the wrap-around case in which __ptr_ring_zero_tail() is invoked and the head and the tail are reset to 0. Since this reset likewise moves the tail to the head, the same detection logic applies. Co-developed-by: Tim Gebauer <[email protected]> Signed-off-by: Tim Gebauer <[email protected]> Signed-off-by: Simon Schippers <[email protected]> --- include/linux/ptr_ring.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h index a5a3fa4916d3..7cdae6d1d400 100644 --- a/include/linux/ptr_ring.h +++ b/include/linux/ptr_ring.h @@ -438,6 +438,19 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r, return ret; } +/* Returns true if the consume of the last n elements has created space + * in the ring buffer (i.e., a new element can be produced). + * + * Note: Because of batching, a successful call to __ptr_ring_consume() / + * __ptr_ring_consume_batched() does not guarantee that the next call to + * __ptr_ring_produce() will succeed. + */ +static inline bool __ptr_ring_consume_created_space(struct ptr_ring *r, + int n) +{ + return r->consumer_head - r->consumer_tail < n; +} + /* 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
