Update registered wait registration API

Wrap it in a struct io_uring_cqwait_reg_arg, to allow for future
expansion more easily. If someone were to add a different struct
type to register, for example to include a full signal mask, then
that would then be possible.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

src/include/liburing.h

diff --git a/src/include/liburing.h b/src/include/liburing.h
index cbba6eb..bd845cf 100644
--- a/src/include/liburing.h
+++ b/src/include/liburing.h
@@ -201,7 +201,7 @@
 				 int arg_index);
 
 int io_uring_register_cqwait_reg(struct io_uring *ring,
-				 struct io_uring_reg_wait *arg, int nr);
+				 struct io_uring_reg_wait *reg, int nr);
 int io_uring_resize_rings(struct io_uring *ring, struct io_uring_params *p);
 int io_uring_clone_buffers(struct io_uring *dst, struct io_uring *src);
 int io_uring_register_buffers(struct io_uring *ring, const struct iovec *iovecs,

src/include/liburing/io_uring.h

diff --git a/src/include/liburing/io_uring.h b/src/include/liburing/io_uring.h
index b73deaf..654567d 100644
--- a/src/include/liburing/io_uring.h
+++ b/src/include/liburing/io_uring.h
@@ -804,6 +804,26 @@
 	IORING_REG_WAIT_TS		= (1U << 0),
 };
 
+/*
+ * Argument for IORING_REGISTER_CQWAIT_REG, registering a region of
+ * struct io_uring_reg_wait that can be indexed when io_uring_enter(2) is
+ * called rather than pass in a wait argument structure separately.
+ */
+struct io_uring_cqwait_reg_arg {
+	__u32		flags;
+	__u32		struct_size;
+	__u32		nr_entries;
+	__u32		pad;
+	__u64		user_addr;
+	__u64		pad2[3];
+};
+
+/*
+ * Argument for io_uring_enter(2) with
+ * IORING_GETEVENTS | IORING_ENTER_EXT_ARG_REG set, where the actual argument
+ * is an index into a previously registered fixed wait region described by
+ * the below structure.
+ */
 struct io_uring_reg_wait {
 	struct __kernel_timespec	ts;
 	__u32				min_wait_usec;
@@ -814,6 +834,9 @@
 	__u64				pad2[2];
 };
 
+/*
+ * Argument for io_uring_enter(2) with IORING_GETEVENTS | IORING_ENTER_EXT_ARG
+ */
 struct io_uring_getevents_arg {
 	__u64	sigmask;
 	__u32	sigmask_sz;

src/register.c

diff --git a/src/register.c b/src/register.c
index b245903..6e9bc88 100644
--- a/src/register.c
+++ b/src/register.c
@@ -454,7 +454,14 @@
 }
 
 int io_uring_register_cqwait_reg(struct io_uring *ring,
-				 struct io_uring_reg_wait *arg, int nr)
+				 struct io_uring_reg_wait *reg, int nr)
 {
-	return do_register(ring, IORING_REGISTER_CQWAIT_REG, arg, nr);
+	struct io_uring_cqwait_reg_arg arg = {
+		.flags		= 0,
+		.struct_size	= sizeof(*reg),
+		.nr_entries	= nr,
+		.user_addr	= (unsigned long) (uintptr_t) reg,
+	};
+
+	return do_register(ring, IORING_REGISTER_CQWAIT_REG, &arg, 1);
 }