io_uring: add IOU_STOP_MULTISHOT return code

For multishot we want a way to signal the caller that multishot has ended
but also this might not be an error return.

For example sockets return 0 when closed, which should end a multishot
recv, but still have a CQE with result 0

Introduce IOU_STOP_MULTISHOT which does this and indicates that the return
code is stored inside req->cqe
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220630091231.1456789-7-dylany@fb.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.h

@@ -15,6 +15,13 @@
 enum {
 	IOU_OK			= 0,
 	IOU_ISSUE_SKIP_COMPLETE	= -EIOCBQUEUED,
+
+	/*
+	 * Intended only when both REQ_F_POLLED and REQ_F_APOLL_MULTISHOT
+	 * are set to indicate to the poll runner that multishot should be
+	 * removed and the result is set on req->cqe.res.
+	 */
+	IOU_STOP_MULTISHOT	= -ECANCELED,
 };
 
 struct io_uring_cqe *__io_get_cqe(struct io_ring_ctx *ctx);

io_uring/poll.c

@@ -195,6 +195,7 @@ static void io_poll_remove_entries(struct io_kiocb *req)
 enum {
 	IOU_POLL_DONE = 0,
 	IOU_POLL_NO_ACTION = 1,
+	IOU_POLL_REMOVE_POLL_USE_RES = 2,
 };
 
 /*
@@ -204,6 +205,8 @@ enum {
  * Returns a negative error on failure. IOU_POLL_NO_ACTION when no action require,
  * which is either spurious wakeup or multishot CQE is served.
  * IOU_POLL_DONE when it's done with the request, then the mask is stored in req->cqe.res.
+ * IOU_POLL_REMOVE_POLL_USE_RES indicates to remove multishot poll and that the result
+ * is stored in req->cqe.
  */
 static int io_poll_check_events(struct io_kiocb *req, bool *locked)
 {
@@ -244,6 +247,8 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked)
 				return -ECANCELED;
 		} else {
 			ret = io_poll_issue(req, locked);
+			if (ret == IOU_STOP_MULTISHOT)
+				return IOU_POLL_REMOVE_POLL_USE_RES;
 			if (ret < 0)
 				return ret;
 		}
@@ -268,7 +273,7 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
 	if (ret == IOU_POLL_DONE) {
 		struct io_poll *poll = io_kiocb_to_cmd(req);
 		req->cqe.res = mangle_poll(req->cqe.res & poll->events);
-	} else {
+	} else if (ret != IOU_POLL_REMOVE_POLL_USE_RES) {
 		req->cqe.res = ret;
 		req_set_fail(req);
 	}
@@ -291,7 +296,9 @@ static void io_apoll_task_func(struct io_kiocb *req, bool *locked)
 	io_poll_remove_entries(req);
 	io_poll_tw_hash_eject(req, locked);
 
-	if (!ret)
+	if (ret == IOU_POLL_REMOVE_POLL_USE_RES)
+		io_req_complete_post(req);
+	else if (ret == IOU_POLL_DONE)
 		io_req_task_submit(req, locked);
 	else
 		io_req_complete_failed(req, ret);