[PATCH v4 4/6] liburing: index large CQE's correctly

[Stefan Roesch <shr@fb.com>]

Large CQE's need to take into account that each CQE has double the size.
When the CQE array is indexed, the offset into the array needs to be
changed accordingly.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 src/include/liburing.h | 18 ++++++++++++++++--
 src/queue.c            |  6 +++++-
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/include/liburing.h b/src/include/liburing.h
index c01c231..317963c 100644
--- a/src/include/liburing.h
+++ b/src/include/liburing.h
@@ -188,6 +188,16 @@ int __io_uring_get_cqe(struct io_uring *ring,
 
 #define LIBURING_UDATA_TIMEOUT	((__u64) -1)
 
+/*
+ * Calculates the step size for CQE iteration.
+ * 	For standard CQE's its 1, for big CQE's its two.
+ */
+#define io_uring_cqe_shift(ring)					\
+	(!!((ring)->flags & IORING_SETUP_CQE32))
+
+#define io_uring_cqe_index(ring,ptr,mask)				\
+	(((ptr) & (mask)) << io_uring_cqe_shift(ring))
+
 #define io_uring_for_each_cqe(ring, head, cqe)				\
 	/*								\
 	 * io_uring_smp_load_acquire() enforces the order of tail	\
@@ -195,7 +205,7 @@ int __io_uring_get_cqe(struct io_uring *ring,
 	 */								\
 	for (head = *(ring)->cq.khead;					\
 	     (cqe = (head != io_uring_smp_load_acquire((ring)->cq.ktail) ? \
-		&(ring)->cq.cqes[head & (*(ring)->cq.kring_mask)] : NULL)); \
+		&(ring)->cq.cqes[io_uring_cqe_index(ring, head, *(ring)->cq.kring_mask)] : NULL)); \
 	     head++)							\
 
 /*
@@ -844,6 +854,10 @@ static inline int __io_uring_peek_cqe(struct io_uring *ring,
 	int err = 0;
 	unsigned available;
 	unsigned mask = *ring->cq.kring_mask;
+	int shift = 0;
+
+	if (ring->flags & IORING_SETUP_CQE32)
+		shift = 1;
 
 	do {
 		unsigned tail = io_uring_smp_load_acquire(ring->cq.ktail);
@@ -854,7 +868,7 @@ static inline int __io_uring_peek_cqe(struct io_uring *ring,
 		if (!available)
 			break;
 
-		cqe = &ring->cq.cqes[head & mask];
+		cqe = &ring->cq.cqes[(head & mask) << shift];
 		if (!(ring->features & IORING_FEAT_EXT_ARG) &&
 				cqe->user_data == LIBURING_UDATA_TIMEOUT) {
 			if (cqe->res < 0)
diff --git a/src/queue.c b/src/queue.c
index 2f85756..4ad41fc 100644
--- a/src/queue.c
+++ b/src/queue.c
@@ -132,6 +132,10 @@ unsigned io_uring_peek_batch_cqe(struct io_uring *ring,
 {
 	unsigned ready;
 	bool overflow_checked = false;
+	int shift = 0;
+
+	if (ring->flags & IORING_SETUP_CQE32)
+		shift = 1;
 
 again:
 	ready = io_uring_cq_ready(ring);
@@ -144,7 +148,7 @@ again:
 		count = count > ready ? ready : count;
 		last = head + count;
 		for (;head != last; head++, i++)
-			cqes[i] = &ring->cq.cqes[head & mask];
+			cqes[i] = &ring->cq.cqes[(head & mask) << shift];
 
 		return count;
 	}
-- 
2.30.2