POSIX: Add code for shuffling file descriptors.

base/file_descriptor_shuffle.cc

+// Copyright (c) 2009 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.
+
+#include "base/file_descriptor_shuffle.h"
+
+#include <errno.h>
+#include <unistd.h>
+
+#include "base/logging.h"
+
+namespace base {
+
+bool PerformInjectiveMultimap(const InjectiveMultimap& m_in,
+                              InjectionDelegate* delegate) {
+  InjectiveMultimap m(m_in);
+  std::vector<int> extra_fds;
+
+  for (InjectiveMultimap::iterator i = m.begin(); i != m.end(); ++i) {
+    int temp_fd = -1;
+
+    // We DCHECK the injectiveness of the mapping.
+    for (InjectiveMultimap::iterator j = i + 1; j != m.end(); ++j)
+      DCHECK(i->dest != j->dest);
+
+    const bool is_identity = i->source == i->dest;
+
+    for (InjectiveMultimap::iterator j = i + 1; j != m.end(); ++j) {
+      if (!is_identity && i->dest == j->source) {
+        if (temp_fd == -1) {
+          if (!delegate->Duplicate(&temp_fd, i->dest))
+            return false;
+          extra_fds.push_back(temp_fd);
+        }
+
+        j->source = temp_fd;
+        j->close = false;
+      }
+
+      if (i->close && i->source == j->dest)
+        i->close = false;
+
+      if (i->close && i->source == j->source) {
+        i->close = false;
+        j->close = true;
+      }
+    }
+
+    if (!is_identity) {
+      if (!delegate->Move(i->source, i->dest))
+        return false;
+    }
+
+    if (!is_identity && i->close)
+      delegate->Close(i->source);
+  }
+
+  for (std::vector<int>::const_iterator
+       i = extra_fds.begin(); i != extra_fds.end(); ++i) {
+    delegate->Close(*i);
+  }
+
+  return true;
+}
+
+bool FileDescriptorTableInjection::Duplicate(int* result, int fd) {
+  do {
+    *result = dup(fd);
+  } while(*result == -1 && errno == EINTR);
+
+  return *result >= 0;
+}
+
+bool FileDescriptorTableInjection::Move(int src, int dest) {
+  int result;
+
+  do {
+    result = dup2(src, dest);
+  } while (result == -1 && errno == EINTR);
+
+  return result != -1;
+}
+
+void FileDescriptorTableInjection::Close(int fd) {
+  int result;
+
+  do {
+    result = close(fd);
+  } while (result == -1 && errno == EINTR);
+}
+
+}  // namespace base