liblog: add android_log_logger_list management

Add list of android_log_logger_list entities as a way of
accessing the list of transport contexts from within
one of the transports.  This will enable us to iterate back
to an internal transport context which may house a last index
or signalling semaphore to propagate a wakeup on a blocking
read.

Test: gTest libcutils-tests, logd-unit-tests, liblog-unit-tests,
      logcat-unit-tests
Bug: 27405083
Change-Id: I0a5e793946c020d97ffe10192369998e4ed92a83
diff --git a/liblog/logger_read.c b/liblog/logger_read.c
index c3cb7ad..7e50a23 100644
--- a/liblog/logger_read.c
+++ b/liblog/logger_read.c
@@ -228,6 +228,13 @@
     LOGGER_LIST_FUNCTION(logger_list, -ENODEV, setPrune, buf, len);
 }
 
+LIBLOG_HIDDEN struct listnode __android_log_readers =
+    { &__android_log_readers, &__android_log_readers };
+#if !defined(_WIN32)
+LIBLOG_HIDDEN pthread_rwlock_t __android_log_readers_lock =
+    PTHREAD_RWLOCK_INITIALIZER;
+#endif
+
 LIBLOG_ABI_PUBLIC struct logger_list *android_logger_list_alloc(
         int mode,
         unsigned int tail,
@@ -246,6 +253,10 @@
     logger_list->tail = tail;
     logger_list->pid = pid;
 
+    logger_list_wrlock();
+    list_add_tail(&__android_log_readers, &logger_list->node);
+    logger_list_unlock();
+
     return (struct logger_list *)logger_list;
 }
 
@@ -267,6 +278,10 @@
     logger_list->start = start;
     logger_list->pid = pid;
 
+    logger_list_wrlock();
+    list_add_tail(&__android_log_readers, &logger_list->node);
+    logger_list_unlock();
+
     return (struct logger_list *)logger_list;
 }
 
@@ -502,6 +517,10 @@
         return;
     }
 
+    logger_list_wrlock();
+    list_remove(&logger_list_internal->node);
+    logger_list_unlock();
+
     while (!list_empty(&logger_list_internal->transport)) {
         struct listnode *node = list_head(&logger_list_internal->transport);
         struct android_log_transport_context *transp =