一博客中，一段的注释的解释：[From: http://blog.csdn.net/hustpzb/article/details/8525324]
/** * Access to the system diagnostic event record. System diagnostic events are * used to record certain system-level events (such as garbage collection, * activity manager state, system watchdogs, and other low level activity), * which may be automatically collected and analyzed during system development. * * <p>This is <b>not</b> the main "logcat" debugging log ({@link android.util.Log})! * These diagnostic events are for system integrators, not application authors. * * <p>Events use integer tag codes corresponding to /system/etc/event-log-tags. * They carry a payload of one or more int, long, or String values. The * event-log-tags file defines the payload contents for each type code. */
在Google Andorid代码中：
system/core/include/cutils/event_tag_map.h 第24行
其中另一博客亦有详细的介绍：[From: http://blog.csdn.net/darkengine/article/details/8477502]
总而言之，按个人理解，这个是用来设定、配置输出日志(event log)格式的。