io_uring: support for IO polling

Add support for a polled io_uring instance. When a read or write is
submitted to a polled io_uring, the application must poll for
completions on the CQ ring through io_uring_enter(2). Polled IO may not
generate IRQ completions, hence they need to be actively found by the
application itself.

To use polling, io_uring_setup() must be used with the
IORING_SETUP_IOPOLL flag being set. It is illegal to mix and match
polled and non-polled IO on an io_uring.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 4589d56d0b68..5c457ea396e6 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -30,6 +30,11 @@ struct io_uring_sqe {
         __u64   __pad2[3];
 };
 
+/*
+ * io_uring_setup() flags
+ */
+#define IORING_SETUP_IOPOLL     (1U << 0)       /* io_context is polled */
+
 #define IORING_OP_NOP           0
 #define IORING_OP_READV         1
 #define IORING_OP_WRITEV        2