linux-kernel - [PATCH 0/2] io_uring: add a CQ ring flag to enable/disable eventfd notification

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Message-Id: <20200515105414.68683-1-sgarzare@redhat.com>
Date:   Fri, 15 May 2020 12:54:12 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: [PATCH 0/2] io_uring: add a CQ ring flag to enable/disable eventfd
 notification

The first patch adds the new 'cq_flags' field for the CQ ring. It
should be written by the application and read by the kernel.

The second patch adds a new IORING_CQ_NEED_WAKEUP flag that can be
used by the application to enable/disable eventfd notifications.

I'm not sure the name is the best one, an alternative could be
IORING_CQ_NEED_EVENT.

This feature can be useful if the application are using eventfd to be
notified when requests are completed, but they don't want a notification
for every request.
Of course the application can already remove the eventfd from the event
loop, but as soon as it adds the eventfd again, it will be notified,
even if it has already handled all the completed requests.

The most important use case is when the registered eventfd is used to
notify a KVM guest through irqfd and we want a mechanism to
enable/disable interrupts.

I also extended liburing API and added a test case here:
https://github.com/stefano-garzarella/liburing/tree/eventfd-disable

Stefano Garzarella (2):
  io_uring: add 'cq_flags' field for the CQ ring
  io_uring: add IORING_CQ_NEED_WAKEUP to the CQ ring flags

 fs/io_uring.c                 | 17 ++++++++++++++++-
 include/uapi/linux/io_uring.h |  9 ++++++++-
 2 files changed, 24 insertions(+), 2 deletions(-)

-- 
2.25.4