Add support for serialized property contexts

This adds support for reading a serialized
/dev/__properties__/property_info file, which contains a
serialized trie that maps property names to the SELinux context to
which they belong.

Performance wise on walleye, this change reduces the start up cost in
libc from ~3000us to ~430us.  On a benchmark that calls
__system_property_find() for each property set on the system, it
reduces the time per iteration from ~650us to ~292us.

Bug: 36001741
Test: Boot bullhead, walleye, run unit tests
Test: Benchmark initialization and lookup performance

Change-Id: I0887a3a7da88eb51b6d1bd494fa5bce593423599

1 files changed, 7 insertions, 1 deletions

diff --git a/libc/system_properties/context_node.h b/libc/system_properties/context_node.h
index 1c6cbbb8e..769b85332 100644
--- a/libc/system_properties/context_node.h
+++ b/libc/system_properties/context_node.h
@@ -41,9 +41,16 @@ class ContextNode {
   ~ContextNode() {
     Unmap();
   }
+
+  ContextNode(const ContextNode&) = delete;
+  ContextNode(ContextNode&&) = delete;
+  void operator=(const ContextNode&) = delete;
+  void operator=(const ContextNode&&) = delete;
+
   bool Open(bool access_rw, bool* fsetxattr_failed);
   bool CheckAccessAndOpen();
   void ResetAccess();
+  void Unmap();
 
   const char* context() const {
     return context_;
@@ -54,7 +61,6 @@ class ContextNode {
 
  private:
   bool CheckAccess();
-  void Unmap();
 
   Lock lock_;
   const char* context_;