Create a bootstat library for external C and C++ programs

bootstat.h

Index: bootstat.h
diff --git a/bootstat.h b/bootstat.h
index d198061a93ed3d3dec1ad0ce28124e0554960b44..d6b13d225e61fd0bbcb5f25c4c662281991eaaff 100644
--- a/bootstat.h
+++ b/bootstat.h
@@ -2,6 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// Public API for the C and C++ bindings to the Chromium OS
+// 'bootstat' facility.  The facility is a simple timestamp
+// mechanism to associate a named event with the time that it
+// occurred and with other relevant statistics.
+
 #ifndef BOOTSTAT_H_
 #define BOOTSTAT_H_
 
@@ -9,9 +14,29 @@
 extern "C" {
 #endif
 
-extern void bootstat_log(const char *);
+//
+// Length of the longest valid string naming an event, including the
+// terminating NUL character.  Clients of bootstat_log() can use
+// this value for the size of buffers to hold event names; names
+// that exceed this buffer size will be truncated.
+//
+// This value is arbitrarily chosen, but see comments in
+// bootstat_log.c regarding implementation assumptions for this
+// value.
+//
+#define BOOTSTAT_MAX_EVENT_LEN  64
+
+// Log an event.  Event names should be composed of characters drawn
+// from this subset of 7-bit ASCII:  Letters (upper- or lower-case),
+// digits, dot ('.'), dash ('-'), and underscore ('_').  Case is
+// significant.  Behavior in the presence of other characters is
+// unspecified - Caveat Emptor!
+//
+// Applications are responsible for establishing higher-level naming
+// conventions to prevent name collisions.
+extern void bootstat_log(const char* event_name);
 
 #if defined(__cplusplus)
 }
 #endif
-#endif // BOOTSTAT_H_
+#endif  // BOOTSTAT_H_