nix-worker: put the pid of the caller in argv[1]

This is useful for debugging.

src/libmain/shared.cc

@@ -287,7 +287,7 @@ static void * oomHandler(size_t requested)
 
 
 int exitCode = 0;
-
+char * * argvSaved = 0;
 
 }
 
@@ -298,6 +298,8 @@ int main(int argc, char * * argv)
 {
     using namespace nix;
 
+    argvSaved = argv;
+
     /* If we're setuid, then we need to take some security precautions
        right away. */
     if (argc == 0) abort();

src/libmain/shared.hh

@@ -56,6 +56,8 @@ struct RemoveTempRoots
 /* Exit code of the program. */
 extern int exitCode;
 
+extern char * * argvSaved;
+
 }
 
 

src/nix-worker/nix-worker.cc

@@ -753,8 +753,21 @@ static void daemonLoop()
 		    throw SysError("accepting connection");
             }
 
-            printMsg(lvlInfo, format("accepted connection %1%") % remote);
+            /* Get the identity of the caller, if possible. */
+            uid_t clientUid = -1;
+            pid_t clientPid = -1;
 
+#if defined(SO_PEERCRED)
+            ucred cred;
+            socklen_t credLen = sizeof(cred);
+            if (getsockopt(remote, SOL_SOCKET, SO_PEERCRED, &cred, &credLen) != -1) {
+                clientPid = cred.pid;
+                clientUid = cred.uid;
+            }
+#endif
+
+            printMsg(lvlInfo, format("accepted connection from pid %1%, uid %2%") % clientPid % clientUid);
+            
             /* Fork a child to handle the connection. */
             pid_t child;
             child = fork();
@@ -774,6 +787,12 @@ static void daemonLoop()
                     /* Restore normal handling of SIGCHLD. */
                     setSigChldAction(false);
 
+                    /* For debugging, stuff the pid into argv[1]. */
+                    if (clientPid != -1 && argvSaved[1]) {
+                        string processName = int2String(clientPid);
+                        strncpy(argvSaved[1], processName.c_str(), strlen(argvSaved[1]));
+                    }
+                    
                     /* Since the daemon can be long-running, the
                        settings may have changed.  So force a reload. */
                     reloadSettings();