Log the last error code of StatsLog failures

Test: builds and manual test
Bug: 80538532
Change-Id: I7f9d0e22b7ad4295dd787f6cb409bfb3342a7b27

libstats/include/stats_event_list.h

@@ -24,7 +24,7 @@ extern "C" {
 #endif
 void reset_log_context(android_log_context ctx);
 int write_to_logger(android_log_context context, log_id_t id);
-void note_log_drop();
+void note_log_drop(int error);
 void stats_log_close();
 
 #ifdef __cplusplus

libstats/stats_event_list.c

@@ -120,8 +120,8 @@ int write_to_logger(android_log_context ctx, log_id_t id) {
     return retValue;
 }
 
-void note_log_drop() {
-    statsdLoggerWrite.noteDrop();
+void note_log_drop(int error) {
+    statsdLoggerWrite.noteDrop(error);
 }
 
 void stats_log_close() {

libstats/statsd_writer.c

@@ -48,6 +48,7 @@
 
 static pthread_mutex_t log_init_lock = PTHREAD_MUTEX_INITIALIZER;
 static atomic_int dropped = 0;
+static atomic_int log_error = 0;
 
 void statsd_writer_init_lock() {
     /*
@@ -150,8 +151,9 @@ static int statsdAvailable() {
     return 1;
 }
 
-static void statsdNoteDrop() {
+static void statsdNoteDrop(int error) {
     atomic_fetch_add_explicit(&dropped, 1, memory_order_relaxed);
+    atomic_exchange_explicit(&log_error, error, memory_order_relaxed);
 }
 
 static int statsdWrite(struct timespec* ts, struct iovec* vec, size_t nr) {
@@ -202,7 +204,8 @@ static int statsdWrite(struct timespec* ts, struct iovec* vec, size_t nr) {
         if (snapshot) {
             android_log_event_int_t buffer;
             header.id = LOG_ID_STATS;
-            buffer.header.tag = htole32(LIBLOG_LOG_TAG);
+            // store the last log error in the tag field. This tag field is not used by statsd.
+            buffer.header.tag = htole32(atomic_load(&log_error));
             buffer.payload.type = EVENT_TYPE_INT;
             buffer.payload.data = htole32(snapshot);
 

libstats/statsd_writer.h

@@ -39,7 +39,7 @@ struct android_log_transport_write {
     /* write log to transport, returns number of bytes propagated, or -errno */
     int (*write)(struct timespec* ts, struct iovec* vec, size_t nr);
     /* note one log drop */
-    void (*noteDrop)();
+    void (*noteDrop)(int error);
 };
 
 #endif  // ANDROID_STATS_LOG_STATS_WRITER_H