ChildPortHandshake: allow receive rights to be received

util/mach/child_port.defs

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 #include <mach/mach_types.defs>
 #include <mach/std_types.defs>
 
 // child_port provides an interface for port rights to be transferred between
-// tasks. Its expected usage is for child processes to be able to pass port
-// rights to their parent processes. A child may wish to give its parent a copy
-// of a send right to its own task port, or a child may hold a receive right for
-// a server and wish to furnish its parent with a send right to that server.
+// tasks. Its expected usage is for processes to be able to pass port rights
+// across IPC boundaries. A child process may wish to give its parent a copy of
+// of a send right to its own task port, or a parent process may wish to give a
+// receive right to a child process that implements a server.
 //
 // This Mach subsystem defines the lowest-level interface for these rights to
 // be transferred. Most users will not user this interface directly, but will
 // use ChildPortHandshake, which builds on this interface by providing client
 // and server implementations, along with a protocol for establishing
 // communication in a parent-child process relationship.
 subsystem child_port 10011;
 
 serverprefix handle_;
 
 type child_port_server_t = mach_port_t;
 type child_port_token_t = uint64_t;
 
 import "util/mach/child_port_types.h";
 
 // Sends a Mach port right across an IPC boundary.
 //
 // server[in]: The server to send the port right to.
 // token[in]: A random opaque token, generated by the server and communicated to
 //     the client through some secure means such as a shared pipe. The client
 //     includes the token in its request to prove its authenticity to the
 //     server. This parameter is necessary for instances where the server must
 //     publish its service broadly, such as via the bootstrap server. When this
 //     is done, anyone with access to the bootstrap server will be able to gain
 //     rights to communicate with |server|, and |token| serves as a shared
 //     secret allowing the server to verify that it has received a request from
 //     the intended client. |server| will reject requests with an invalid
 //     |token|.
-// port[in]: A port right to transfer to the server. In expected usage, this may
-//     be a send or send-once right, and the |server| will reject a receive
-//     right. It is permissible to specify make-send for a receive right.
+// port[in]: A port right to transfer to the server.
 //
 // Return value: As this is a “simpleroutine”, the server does not respond to
 //     the client request, and the client does not block waiting for a response
 //     after sending its request. The return value is MACH_MSG_SUCCESS if the
 //     request was queued for the server, without any indication of whether the
 //     server considered the request valid or took any action. On data
 //     validation or mach_msg() failure, another code will be returned
 //     indicating the nature of the error.
 simpleroutine child_port_check_in(server: child_port_server_t;
                                   token: child_port_token_t;
                                   port: mach_port_poly_t);