Extend UnixDomainSocket::RecvMsg to return sender's PID

base/posix/unix_domain_socket_linux.h

Index: base/posix/unix_domain_socket_linux.h
diff --git a/base/posix/unix_domain_socket_linux.h b/base/posix/unix_domain_socket_linux.h
index 66fb8bb1bf629894c5badb4564cf517a5e4ded71..c22dd46ceb1237ec979bd965e047316fcb3fe0bc 100644
--- a/base/posix/unix_domain_socket_linux.h
+++ b/base/posix/unix_domain_socket_linux.h
@@ -10,6 +10,7 @@
 #include <vector>
 
 #include "base/base_export.h"
+#include "base/process/process_handle.h"
 
 class Pickle;
 
@@ -18,6 +19,9 @@ class BASE_EXPORT UnixDomainSocket {
   // Maximum number of file descriptors that can be read by RecvMsg().
   static const size_t kMaxFileDescriptors;
 
+  // Use to enable receiving pids in RecvMsg.  Returns true if successful.
+  static bool EnableReceiveProcessId(int fd);

[jln (very slow on Chromium), 2014/04/24 18:32:58]

Perhaps make it clear that this should be used on the receiving end?

[mdempsky, 2014/04/24 19:00:34]

Done.

+
   // Use sendmsg to write the given msg and include a vector of file
   // descriptors. Returns true if successful.
   static bool SendMsg(int fd,
@@ -32,6 +36,15 @@ class BASE_EXPORT UnixDomainSocket {
                          size_t length,
                          std::vector<int>* fds);
 
+  // Same as RecvMsg above, but also returns the sender's PID (as seen from
+  // the caller's namespace).  However, before using this function to receive
+  // PIDs, EnableReceiveProcessId() should be called on the socket.
+  static ssize_t RecvMsgWithPid(int fd,
+                                void* msg,
+                                size_t length,
+                                std::vector<int>* fds,
+                                base::ProcessId* pid);
+
   // Perform a sendmsg/recvmsg pair.
   //   1. This process creates a UNIX SEQPACKET socketpair. Using
   //      connection-oriented sockets (SEQPACKET or STREAM) is critical here,
@@ -70,7 +83,8 @@ class BASE_EXPORT UnixDomainSocket {
                                   void* msg,
                                   size_t length,
                                   int flags,
-                                  std::vector<int>* fds);
+                                  std::vector<int>* fds,
+                                  base::ProcessId* pid);

[jln (very slow on Chromium), 2014/04/24 18:32:58]

You didn't have to modify any caller? I was pretty sure RecvMsgWithFlags was
used (I think I added it).

[mdempsky, 2014/04/24 19:00:34]

It has 'private' visibility, so it's only used within
unix_domain_socket_linux.cc, and I fixed up the one caller in there (in
SendRecvMsgWithFlags).

 };
 
 #endif  // BASE_POSIX_UNIX_DOMAIN_SOCKET_LINUX_H_