[PATCH liburing 5/5] src/queue: fix no-error with NULL cqe

[Pavel Begunkov <asml.silence@gmail.com>]

Can happen that _io_uring_get_cqe() returns success without filled cqe,
and it's ok, especially for wait_n=0. Fix up error code for functions
that always want to have a valid CQE on success.

Also don't do cq_ring_needs_flush() check in a some weird place,
mainstream it together with wait_nr testing.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 src/include/liburing.h |  4 +++-
 src/queue.c            | 10 +---------
 2 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/src/include/liburing.h b/src/include/liburing.h
index 90403bc..27c5a14 100644
--- a/src/include/liburing.h
+++ b/src/include/liburing.h
@@ -601,7 +601,9 @@ static inline int io_uring_wait_cqe_nr(struct io_uring *ring,
 				      struct io_uring_cqe **cqe_ptr,
 				      unsigned wait_nr)
 {
-	return __io_uring_get_cqe(ring, cqe_ptr, 0, wait_nr, NULL);
+	int ret = __io_uring_get_cqe(ring, cqe_ptr, 0, wait_nr, NULL);
+
+	return (ret || *cqe_ptr) ? ret : -EAGAIN;
 }
 
 /*
diff --git a/src/queue.c b/src/queue.c
index 4fb4ea7..0b09a9c 100644
--- a/src/queue.c
+++ b/src/queue.c
@@ -93,7 +93,6 @@ static int _io_uring_get_cqe(struct io_uring *ring, struct io_uring_cqe **cqe_pt
 
 	do {
 		bool need_enter = false;
-		bool cq_overflow_flush = false;
 		unsigned flags = 0;
 		unsigned nr_available;
 		int ret;
@@ -101,14 +100,7 @@ static int _io_uring_get_cqe(struct io_uring *ring, struct io_uring_cqe **cqe_pt
 		err = __io_uring_peek_cqe(ring, &cqe, &nr_available);
 		if (err)
 			break;
-		if (!cqe && !to_wait && !data->submit) {
-			if (!cq_ring_needs_flush(ring)) {
-				err = -EAGAIN;
-				break;
-			}
-			cq_overflow_flush = true;
-		}
-		if (data->wait_nr > nr_available || cq_overflow_flush) {
+		if (data->wait_nr > nr_available || cq_ring_needs_flush(ring)) {
 			flags = IORING_ENTER_GETEVENTS | data->get_flags;
 			need_enter = true;
 		}
-- 
2.24.0