Split system_properties.cpp into its component pieces

system_properties.cpp is a little bit unmanageable in its current
form, and is overdue for a refactoring into more clearly defined
components.

Of particular interest, is creating of a Contexts interface that
handles mapping of system property name -> SEContext and its
associated prop_area, and creating two classes that implement the
current and legacy functionality.  This is needed as there will likely
be a third even newer way to do this mapping.

Bug: 36001741
Test: boot bullhead, system property unit tests
Change-Id: Ie75ec6fea1a95f90813918f54669d533e51327c6
diff --git a/libc/system_properties/context_node.h b/libc/system_properties/context_node.h
new file mode 100644
index 0000000..1c6cbbb
--- /dev/null
+++ b/libc/system_properties/context_node.h
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef SYSTEM_PROPERTIES_CONTEXT_NODE_H
+#define SYSTEM_PROPERTIES_CONTEXT_NODE_H
+
+#include "private/bionic_lock.h"
+
+#include "prop_area.h"
+
+class ContextNode {
+ public:
+  ContextNode(const char* context) : context_(context), pa_(nullptr), no_access_(false) {
+    lock_.init(false);
+  }
+  ~ContextNode() {
+    Unmap();
+  }
+  bool Open(bool access_rw, bool* fsetxattr_failed);
+  bool CheckAccessAndOpen();
+  void ResetAccess();
+
+  const char* context() const {
+    return context_;
+  }
+  prop_area* pa() {
+    return pa_;
+  }
+
+ private:
+  bool CheckAccess();
+  void Unmap();
+
+  Lock lock_;
+  const char* context_;
+  prop_area* pa_;
+  bool no_access_;
+};
+
+#endif