Add callback hack to find out when to reload system properties.

Every IBinder object can accept a new transaction to tell it that
it might want to reload system properties, and in the process
anyone can register a callback to be executed when this happens.

Use this to reload the trace property.

This is very much ONLY for debugging.

Change-Id: I55c67c46f8f3fa9073bef0dfaab4577ed1d47eb4

3 files changed, 10 insertions, 0 deletions

diff --git a/include/binder/IBinder.h b/include/binder/IBinder.h
index 81b56c2..8b84951 100644
--- a/include/binder/IBinder.h
+++ b/include/binder/IBinder.h
@@ -51,6 +51,7 @@ public:
         PING_TRANSACTION        = B_PACK_CHARS('_','P','N','G'),
         DUMP_TRANSACTION        = B_PACK_CHARS('_','D','M','P'),
         INTERFACE_TRANSACTION   = B_PACK_CHARS('_', 'N', 'T', 'F'),
+        SYSPROPS_TRANSACTION    = B_PACK_CHARS('_', 'S', 'P', 'R'),
 
         // Corresponds to TF_ONE_WAY -- an asynchronous call.
         FLAG_ONEWAY             = 0x00000001
diff --git a/include/utils/Trace.h b/include/utils/Trace.h
index 62f5d6b..984cd46 100644
--- a/include/utils/Trace.h
+++ b/include/utils/Trace.h
@@ -121,11 +121,16 @@ private:
         }
     }
 
+    static void changeCallback();
+
     // init opens the trace marker file for writing and reads the
     // atrace.tags.enableflags system property.  It does this only the first
     // time it is run, using sMutex for synchronization.
     static void init();
 
+    // retrieve the current value of the system property.
+    static void loadSystemProperty();
+
     // sIsReady is a boolean value indicating whether a call to init() has
     // completed in this process.  It is initialized to 0 and set to 1 when the
     // first init() call completes.  It is set to 1 even if a failure occurred
diff --git a/include/utils/misc.h b/include/utils/misc.h
index 23f2a4c..d7d5bc1 100644
--- a/include/utils/misc.h
+++ b/include/utils/misc.h
@@ -88,6 +88,10 @@ void strreverse(char* begin, char* end);
 void k_itoa(int value, char* str, int base);
 char* itoa(int val, int base);
 
+typedef void (*sysprop_change_callback)(void);
+void add_sysprop_change_callback(sysprop_change_callback cb, int priority);
+void report_sysprop_change();
+
 }; // namespace android
 
 #endif // _LIBS_UTILS_MISC_H