io_uring: disable multishot recvmsg

recvmsg has semantics that do not make it trivial to extend to
multishot. Specifically it has user pointers and returns data in the
original parameter. In order to make this API useful these will need to be
somehow included with the provided buffers.

For now remove multishot for recvmsg as it is not useful.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220704140106.200167-1-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/net.c

@@ -409,6 +409,8 @@ int io_recvmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (sr->msg_flags & MSG_ERRQUEUE)
 		req->flags |= REQ_F_CLEAR_POLLIN;
 	if (sr->flags & IORING_RECV_MULTISHOT) {
+		if (req->opcode == IORING_OP_RECVMSG)
+			return -EINVAL;
 		if (!(req->flags & REQ_F_BUFFER_SELECT))
 			return -EINVAL;
 		if (sr->msg_flags & MSG_WAITALL)
@@ -435,7 +437,7 @@ static inline void io_recv_prep_retry(struct io_kiocb *req)
 }
 
 /*
- * Finishes io_recv and io_recvmsg.
+ * Finishes io_recv
  *
  * Returns true if it is actually finished, or false if it should run
  * again (for multishot).
@@ -477,7 +479,6 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
 	unsigned flags;
 	int ret, min_ret = 0;
 	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
-	size_t len = sr->len;
 
 	sock = sock_from_file(req->file);
 	if (unlikely(!sock))
@@ -496,17 +497,16 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
 	    (sr->flags & IORING_RECVSEND_POLL_FIRST))
 		return io_setup_async_msg(req, kmsg);
 
-retry_multishot:
 	if (io_do_buffer_select(req)) {
 		void __user *buf;
 
-		buf = io_buffer_select(req, &len, issue_flags);
+		buf = io_buffer_select(req, &sr->len, issue_flags);
 		if (!buf)
 			return -ENOBUFS;
 		kmsg->fast_iov[0].iov_base = buf;
-		kmsg->fast_iov[0].iov_len = len;
+		kmsg->fast_iov[0].iov_len = sr->len;
 		iov_iter_init(&kmsg->msg.msg_iter, READ, kmsg->fast_iov, 1,
-				len);
+				sr->len);
 	}
 
 	flags = sr->msg_flags;
@@ -518,15 +518,8 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
 	kmsg->msg.msg_get_inq = 1;
 	ret = __sys_recvmsg_sock(sock, &kmsg->msg, sr->umsg, kmsg->uaddr, flags);
 	if (ret < min_ret) {
-		if (ret == -EAGAIN && force_nonblock) {
-			ret = io_setup_async_msg(req, kmsg);
-			if (ret == -EAGAIN && (req->flags & IO_APOLL_MULTI_POLLED) ==
-					       IO_APOLL_MULTI_POLLED) {
-				io_kbuf_recycle(req, issue_flags);
-				return IOU_ISSUE_SKIP_COMPLETE;
-			}
-			return ret;
-		}
+		if (ret == -EAGAIN && force_nonblock)
+			return io_setup_async_msg(req, kmsg);
 		if (ret == -ERESTARTSYS)
 			ret = -EINTR;
 		if (ret > 0 && io_net_retry(sock, flags)) {
@@ -554,10 +547,8 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
 	if (kmsg->msg.msg_inq)
 		cflags |= IORING_CQE_F_SOCK_NONEMPTY;
 
-	if (!io_recv_finish(req, &ret, cflags))
-		goto retry_multishot;
-
-	return ret;
+	io_req_set_res(req, ret, cflags);
+	return IOU_OK;
 }
 
 int io_recv(struct io_kiocb *req, unsigned int issue_flags)