Use RecvMsgWithPid to find real PID for zygote children

content/public/common/zygote_fork_delegate_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_PUBLIC_COMMON_ZYGOTE_FORK_DELEGATE_LINUX_H_
 #define CONTENT_PUBLIC_COMMON_ZYGOTE_FORK_DELEGATE_LINUX_H_
 
 #include <unistd.h>
 
 #include <string>
@@ skipping 31 matching lines @@
   // Returns 'true' if the delegate would like to handle a given fork
   // request.  Otherwise returns false.  Optionally, fills in uma_name et al
   // with a report the helper wants to make via UMA_HISTOGRAM_ENUMERATION.
   virtual bool CanHelp(const std::string& process_type, std::string* uma_name,
                        int* uma_sample, int* uma_boundary_value) = 0;
 
   // Indexes of FDs in the vector passed to Fork().
   enum {
     // Used to pass in the descriptor for talking to the Browser
     kBrowserFDIndex,
-    // The next two are used in the protocol for discovering the
-    // child processes real PID from within the SUID sandbox. See
-    // http://code.google.com/p/chromium/wiki/LinuxZygote
-    kDummyFDIndex,
-    kParentFDIndex,
+    // The PID oracle is used in the protocol for discovering the
+    // child process's real PID from within the SUID sandbox.
+    // The child process is required to write to the socket after
+    // successfully forking.
+    kPIDOracleFDIndex,
     kNumPassedFDs  // Number of FDs in the vector passed to Fork().
   };
 
   // Delegate forks, returning a -1 on failure. Outside the
   // suid sandbox, Fork() returns the Linux process ID.
   // This method is not aware of any potential pid namespaces, so it'll
   // return a raw pid just like fork() would.
   // Delegate is responsible for communicating the channel ID to the
   // newly created child process.
   virtual pid_t Fork(const std::string& process_type,
                      const std::vector<int>& fds,
                      const std::string& channel_id) = 0;
 
   // The fork delegate must also assume the role of waiting for its children
   // since the caller will not be their parents and cannot do it. |pid| here
   // should be a pid that has been returned by the Fork() method. i.e. This
   // method is completely unaware of eventual PID namespaces due to sandboxing.
   // |known_dead| indicates that the process is already dead and that a
   // blocking wait() should be performed. In this case, GetTerminationStatus()
   // will send a SIGKILL to the target process first.
   virtual bool GetTerminationStatus(pid_t pid, bool known_dead,
                                     base::TerminationStatus* status,
                                     int* exit_code) = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_ZYGOTE_FORK_DELEGATE_LINUX_H_