Add the child_port Mach subsystem

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.
+//
+// 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";

[Robert Sesek, 2014/11/24 20:33:03]

Do you need to define the Mach types above if you include this header?

[Mark Mentovai, 2014/11/24 20:42:28]

Robert Sesek wrote:
Yup. MIG reads the types above, but doesn’t generate C typedefs for them.
child_port_types.h is necessary to provide equivalent typedefs for C/C++ code.
It’s silly, because MIG could write typedefs, it just doesn’t.

This “import” line just tells MIG to output an #include for this file. It
doesn’t actually open child_port_types.h itself or understand how to parse the C
code in there to read the typedefs.

[Robert Sesek, 2014/11/24 20:45:12]

MIG is weird. You'd expect it to either generate typedefs or to process a C
header with the types.

+
+// 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.
+//
+// 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);