[mojo] Add CreateSharedBuffer method to Broker.

mojo/edk/system/broker_messages.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_EDK_SYSTEM_BROKER_MESSAGES_H_
 #define MOJO_EDK_SYSTEM_BROKER_MESSAGES_H_
 
 #include <stdint.h>
 
 #include "base/compiler_specific.h"
 #include "base/process/process_handle.h"
 
 namespace mojo {
 namespace edk {
 
 // This header defines the message format between ChildBroker and
 // ChildBrokerHost.
 
+// Sandbox processes need the parent's help to create shared buffers.
+// They are sent synchronously from child to parent and each have
+// a response. They are sent over a raw pipe.
+enum SandboxMessages {

[Anand Mistry (off Chromium), 2016/01/07 04:36:33]

Not your fault, but these should have a uint32_t size declaration. Without it,
an enum size can vary based on platform, and use in a serialised struct could
cause crashes if you transfer between a 32 and 64 bit process. In Chrome,
there's at least one case where this is possible (NaCl, which is always ILP32).

Maybe you can make this change to all the enums here in a separate CL.

Also, I don't see any packed declarations. These should be added to any
serialised structures.

[Eliot Courtney, 2016/01/07 05:01:30]

Acknowledged.

 #if defined(OS_WIN)
-// Windows only messages needed because sandboxed child processes need the
-// parent's help. They are sent synchronously from child to parent and each have
-// a response. They are sent over a raw pipe.
-enum WindowsSandboxMessages {
   // The reply is two HANDLEs.
   CREATE_PLATFORM_CHANNEL_PAIR = 0,
   // The reply is tokens of the same count of passed in handles.
   HANDLE_TO_TOKEN,
   // The reply is handles of the same count of passed in tokens.
   TOKEN_TO_HANDLE,
+#else
+  // The reply is a PlatformHandle.
+  CREATE_SHARED_BUFFER = 0,
+#endif
 };
 
 // Definitions of the raw bytes sent in messages.
 
 struct BrokerMessage {
   uint32_t size;
-  WindowsSandboxMessages id;
+  SandboxMessages id;
+
+#if defined(OS_WIN)
   // Data, if any, follows.
   union {
     HANDLE handles[1];  // If HANDLE_TO_TOKEN.
     uint64_t tokens[1];  // If TOKEN_TO_HANDLE.
   };
+#else
+  uint32_t num_bytes;  // Size of the shared buffer to create.

[Anand Mistry (off Chromium), 2016/01/07 04:36:33]

Maybe call it shared_buffer_size instead. num_bytes is pretty non-descriptive.

[Eliot Courtney, 2016/01/07 05:01:30]

Done.

+#endif
 };
 
-const int kBrokerMessageHeaderSize =
-  sizeof(uint32_t) + sizeof(WindowsSandboxMessages);
-
-#endif
+const int kBrokerMessageHeaderSize = sizeof(uint32_t) + sizeof(SandboxMessages);
 
 // Route id used for messages between ChildBroker and ChildBrokerHost.
 const uint64_t kBrokerRouteId = 1;
 
 // Multiplexing related messages. They are all asynchronous messages.
 // They are sent over RawChannel.
 enum MultiplexMessages {
   // Messages from child to parent.
   CONNECT_MESSAGE_PIPE = 0,
   CANCEL_CONNECT_MESSAGE_PIPE,
@@ skipping 18 matching lines @@
 struct PeerPipeConnectedMessage {
   MultiplexMessages type;  // PEER_PIPE_CONNECTED
   uint64_t pipe_id;
   base::ProcessId process_id;
 };
 
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_BROKER_MESSAGES_H_