Add the MultiprocessExec test and its test

util/test/posix/close_multiple.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 59 matching lines @@
     }
   }
 };
 
 typedef scoped_ptr<DIR, ScopedDIRCloser> ScopedDIR;
 
 // This function implements CloseMultipleNowOrOnExec() using an operating
 // system-specific FD directory to determine which file descriptors are open.
 // This is an advantage over looping over all possible file descriptors, because
 // no attempt needs to be made to close file descriptors that are not open.
-bool CloseMultipleNowOrOnExecUsingFDDir(int fd) {
+bool CloseMultipleNowOrOnExecUsingFDDir(int fd, int preserve_fd) {
 #if defined(OS_MACOSX)
   const char kFDDir[] = "/dev/fd";
 #elif defined(OS_LINUX)
   const char kFDDir[] = "/proc/self/fd";
 #endif
 
   DIR* dir = opendir(kFDDir);
   if (!dir) {
     PLOG(WARNING) << "opendir";
     return false;
@@ skipping 22 matching lines @@
       LOG(ERROR) << "unexpected entry " << entry_name;
       return false;
     }
 
     int entry_fd;
     if (!AssignIfInRange(&entry_fd, entry_fd_long)) {
       LOG(ERROR) << "out-of-range fd " << entry_name;
       return false;
     }
 
-    if (entry_fd >= fd && entry_fd != dir_fd) {
+    if (entry_fd >= fd && entry_fd != preserve_fd && entry_fd != dir_fd) {
       CloseNowOrOnExec(entry_fd, false);
     }
   }
 
   return true;
 }
 
 }  // namespace
 
-void CloseMultipleNowOrOnExec(int fd) {
-  if (CloseMultipleNowOrOnExecUsingFDDir(fd)) {
-   return;
+void CloseMultipleNowOrOnExec(int fd, int preserve_fd) {
+  if (CloseMultipleNowOrOnExecUsingFDDir(fd, preserve_fd)) {
+    return;
   }
 
   // Fallback: close every file descriptor starting at |fd| and ending at the
   // system’s file descriptor limit. Check a few values and use the highest as
   // the limit, because these may be based on the file descriptor limit set by
   // setrlimit(), and higher-numbered file descriptors may have been opened
   // prior to the limit being lowered. For Mac OS X, see 10.9.2
   // Libc-997.90.3/gen/FreeBSD/sysconf.c sysconf() and 10.9.4
   // xnu-2422.110.17/bsd/kern/kern_descrip.c getdtablesize(), which both return
   // the current RLIMIT_NOFILE value, not the maximum possible file descriptor.
   int max_fd = std::max(static_cast<int>(sysconf(_SC_OPEN_MAX)), OPEN_MAX);
   max_fd = std::max(max_fd, getdtablesize());
 
   for (int entry_fd = fd; entry_fd < max_fd; ++entry_fd) {
-    CloseNowOrOnExec(entry_fd, true);
+    if (entry_fd != preserve_fd) {
+      CloseNowOrOnExec(entry_fd, true);
+    }
   }
 }
 
 }  // namespace crashpad