net/handshake: convert handshake_nl_accept_doit() to FD_PREPARE()

Link: https://patch.msgid.link/20251123-work-fd-prepare-v4-27-b6efa1706cfd@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

net/handshake/netlink.c

@@ -93,7 +93,7 @@ int handshake_nl_accept_doit(struct sk_buff *skb, struct genl_info *info)
 	struct handshake_net *hn = handshake_pernet(net);
 	struct handshake_req *req = NULL;
 	struct socket *sock;
-	int class, fd, err;
+	int class, err;
 
 	err = -EOPNOTSUPP;
 	if (!hn)
@@ -106,27 +106,25 @@ int handshake_nl_accept_doit(struct sk_buff *skb, struct genl_info *info)
 
 	err = -EAGAIN;
 	req = handshake_req_next(hn, class);
-	if (!req)
-		goto out_status;
-
-	sock = req->hr_sk->sk_socket;
-	fd = get_unused_fd_flags(O_CLOEXEC);
-	if (fd < 0) {
-		err = fd;
-		goto out_complete;
-	}
-
-	err = req->hr_proto->hp_accept(req, info, fd);
-	if (err) {
-		put_unused_fd(fd);
-		goto out_complete;
+	if (req) {
+		sock = req->hr_sk->sk_socket;
+
+		FD_PREPARE(fdf, O_CLOEXEC, sock->file);
+		if (fdf.err) {
+			err = fdf.err;
+			goto out_complete;
+		}
+
+		get_file(sock->file); /* FD_PREPARE() consumes a reference. */
+		err = req->hr_proto->hp_accept(req, info, fd_prepare_fd(fdf));
+		if (err)
+			goto out_complete; /* Automatic cleanup handles fput */
+
+		trace_handshake_cmd_accept(net, req, req->hr_sk, fd_prepare_fd(fdf));
+		fd_publish(fdf);
+		return 0;
 	}
 
-	fd_install(fd, get_file(sock->file));
-
-	trace_handshake_cmd_accept(net, req, req->hr_sk, fd);
-	return 0;
-
 out_complete:
 	handshake_complete(req, -EIO, NULL);
 out_status: