add io_uring_queue_mmap

io_uring_queue_init does not allow the caller to specify sq_thread_cpu
or sq_thread_idle.  Users that want to specify those parameters need to
call io_uring_setup(2) themselves.  Add a helper so that they don't also
have to hand-craft the code to map the submission and completion queues,
and setup the sqe ring.  This allows those applications to still make
use of io_uring_submit and get/wait_completion.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 21 insertions, 6 deletions

diff --git a/src/liburing.h b/src/liburing.h
index 623556a..2e7303c 100644
--- a/src/liburing.h
+++ b/src/liburing.h
@@ -56,6 +56,8 @@ extern int io_uring_register(int fd, unsigned int opcode, void *arg,
  */
 extern int io_uring_queue_init(unsigned entries, struct io_uring *ring,
 	unsigned flags);
+extern int io_uring_queue_mmap(int fd, struct io_uring_params *p,
+	struct io_uring *ring);
 extern void io_uring_queue_exit(struct io_uring *ring);
 extern int io_uring_get_completion(struct io_uring *ring,
 	struct io_uring_cqe **cqe_ptr);
diff --git a/src/setup.c b/src/setup.c
index eeb5fef..9979dd0 100644
--- a/src/setup.c
+++ b/src/setup.c
@@ -58,13 +58,30 @@ err:
 }
 
 /*
+ * For users that want to specify sq_thread_cpu or sq_thread_idle, this
+ * interface is a convenient helper for mmap()ing the rings.
+ * Returns -1 on error, or zero on success.  On success, 'ring'
+ * contains the necessary information to read/write to the rings.
+ */
+int io_uring_queue_mmap(int fd, struct io_uring_params *p, struct io_uring *ring)
+{
+	int ret;
+
+	memset(ring, 0, sizeof(*ring));
+	ret = io_uring_mmap(fd, p, &ring->sq, &ring->cq);
+	if (!ret)
+		ring->ring_fd = fd;
+	return ret;
+}
+
+/*
  * Returns -1 on error, or zero on success. On success, 'ring'
  * contains the necessary information to read/write to the rings.
  */
 int io_uring_queue_init(unsigned entries, struct io_uring *ring, unsigned flags)
 {
 	struct io_uring_params p;
-	int fd, ret;
+	int fd;
 
 	memset(&p, 0, sizeof(p));
 	p.flags = flags;
@@ -73,11 +90,7 @@ int io_uring_queue_init(unsigned entries, struct io_uring *ring, unsigned flags)
 	if (fd < 0)
 		return fd;
 
-	memset(ring, 0, sizeof(*ring));
-	ret = io_uring_mmap(fd, &p, &ring->sq, &ring->cq);
-	if (!ret)
-		ring->ring_fd = fd;
-	return ret;
+	return io_uring_queue_mmap(fd, &p, ring);
 }
 
 void io_uring_queue_exit(struct io_uring *ring)