Use RecvMsgWithPid to find real PID for zygote children

content/common/zygote_commands_linux.h

 // Copyright (c) 2012 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 CONTENT_COMMON_ZYGOTE_COMMANDS_LINUX_H_
 #define CONTENT_COMMON_ZYGOTE_COMMANDS_LINUX_H_
 
 #include "base/posix/global_descriptors.h"
 #include "ipc/ipc_descriptors.h"
 
 namespace content {
 
 // Contents of the initial message sent from the zygote to the browser right
 // after it starts.
 static const char kZygoteBootMessage[] = "ZYGOTE_BOOT";
 
 // Contents of the initial message sent from the zygote to the browser when it
 // is ready to go.
 static const char kZygoteHelloMessage[] = "ZYGOTE_OK";
 
+// Message sent by zygote children to the browser so it can discover their

[Mark Seaborn, 2014/05/06 23:34:13]

Nit: to disambiguate -- "so the browser can discover the zygote child's process
ID" perhaps?

[mdempsky, 2014/05/07 05:39:25]

Done.

+// process ID.
+static const char kZygoteChildPingMessage[] = "CHILD_PING";
+
 // Maximum allowable length for messages sent to the zygote.
 const size_t kZygoteMaxMessageLength = 8192;
 
 // File descriptors initialized by the Zygote Host
 const int kZygoteSocketPairFd =
     kPrimaryIPCChannel + base::GlobalDescriptors::kBaseDescriptor;
 
 // These are the command codes used on the wire between the browser and the
 // zygote.
 enum {
   // Fork off a new renderer.
   kZygoteCommandFork = 0,
 
   // Reap a renderer child.
   kZygoteCommandReap = 1,
 
   // Check what happened to a child process.
   kZygoteCommandGetTerminationStatus = 2,
 
   // Read a bitmask of kSandboxLinux*
-  kZygoteCommandGetSandboxStatus = 3
+  kZygoteCommandGetSandboxStatus = 3,
+
+  // Not a real zygote command, but a subcommand used during the zygote fork
+  // protocol.  Sends the child's PID as seen from the browser process.
+  kZygoteCommandForkRealPID = 4
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_ZYGOTE_COMMANDS_LINUX_H_