linux-kernel - [PATCH v2 2/2] io_uring: add IORING_CQ_EVENTFD

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Date:   Fri, 15 May 2020 18:38:05 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        io-uring@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH v2 2/2] io_uring: add IORING_CQ_EVENTFD_DISABLED to the CQ ring flags

This new flag should be set/clear from the application to
disable/enable eventfd notifications when a request is completed
and queued to the CQ ring.

Before this patch, notifications were always sent if an eventfd is
registered, so IORING_CQ_EVENTFD_DISABLED is not set during the
initialization.

It will be up to the application to set the flag after initialization
if no notifications are required at the beginning.

Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
---
v1 -> v2:
 - changed the flag name and behaviour from IORING_CQ_NEED_EVENT to
   IORING_CQ_EVENTFD_DISABLED [Jens]
---
 fs/io_uring.c                 | 2 ++
 include/uapi/linux/io_uring.h | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6e8158269f3c..a9b194e9b5bd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1152,6 +1152,8 @@ static inline bool io_should_trigger_evfd(struct io_ring_ctx *ctx)
 {
 	if (!ctx->cq_ev_fd)
 		return false;
+	if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED)
+		return false;
 	if (!ctx->eventfd_async)
 		return true;
 	return io_wq_current_is_worker();
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 602bb0ece607..8c5775df08b8 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/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