[PATCH liburing 3/5] Add helpers to set and get eventfd notification status

[Stefano Garzarella <sgarzare@redhat.com>]

This patch adds the new IORING_CQ_EVENTFD_DISABLED flag. It can be
used to disable/enable notifications from the kernel when a
request is completed and queued to the CQ ring.

We also add two helpers function to check if the notifications are
enabled and to enable/disable them.

If the kernel doesn't provide CQ ring flags, the notifications are
always enabled if an eventfd is registered.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 src/include/liburing.h          | 30 ++++++++++++++++++++++++++++++
 src/include/liburing/io_uring.h |  7 +++++++
 2 files changed, 37 insertions(+)

diff --git a/src/include/liburing.h b/src/include/liburing.h
index ea596f6..fe03547 100644
--- a/src/include/liburing.h
+++ b/src/include/liburing.h
@@ -9,7 +9,9 @@ extern "C" {
 #include <sys/socket.h>
 #include <sys/uio.h>
 #include <sys/stat.h>
+#include <errno.h>
 #include <signal.h>
+#include <stdbool.h>
 #include <inttypes.h>
 #include <time.h>
 #include "liburing/compat.h"
@@ -445,6 +447,34 @@ static inline unsigned io_uring_cq_ready(struct io_uring *ring)
 	return io_uring_smp_load_acquire(ring->cq.ktail) - *ring->cq.khead;
 }
 
+static inline int io_uring_cq_eventfd_enable(struct io_uring *ring,
+					     bool enabled)
+{
+	uint32_t flags;
+
+	if (!ring->cq.kflags)
+		return -ENOTSUP;
+
+	flags = *ring->cq.kflags;
+
+	if (enabled)
+		flags &= ~IORING_CQ_EVENTFD_DISABLED;
+	else
+		flags |= IORING_CQ_EVENTFD_DISABLED;
+
+	IO_URING_WRITE_ONCE(*ring->cq.kflags, flags);
+
+	return 0;
+}
+
+static inline bool io_uring_cq_eventfd_enabled(struct io_uring *ring)
+{
+	if (!ring->cq.kflags)
+		return true;
+
+	return !(*ring->cq.kflags & IORING_CQ_EVENTFD_DISABLED);
+}
+
 static int __io_uring_peek_cqe(struct io_uring *ring, struct io_uring_cqe **cqe_ptr)
 {
 	struct io_uring_cqe *cqe;
diff --git a/src/include/liburing/io_uring.h b/src/include/liburing/io_uring.h
index 602bb0e..8c5775d 100644
--- a/src/include/liburing/io_uring.h
+++ b/src/include/liburing/io_uring.h
@@ -209,6 +209,13 @@ struct io_cqring_offsets {
 	__u64 resv2;
 };
 
+/*
+ * cq_ring->flags
+ */
+
+/* disable eventfd notifications */
+#define IORING_CQ_EVENTFD_DISABLED	(1U << 0)
+
 /*
  * io_uring_enter(2) flags
  */
-- 
2.25.4