Merge "Improve docs for the tzdata file" am: acf7059a96

Original change: https://android-review.googlesource.com/c/platform/system/timezone/+/1478316

Change-Id: I4c30b8de13f4a2d54aff4518259ef4413b9ded2e
diff --git a/output_data/iana/Android.bp b/output_data/iana/Android.bp
index 650549a..2dd51b9 100644
--- a/output_data/iana/Android.bp
+++ b/output_data/iana/Android.bp
@@ -12,16 +12,25 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// Build rules related to the tzdata file.
+// tzdata is a binary file used by bionic functions like mktime / localtime and
+// Android's implementation of java.util.TimeZone, ZoneInfoDb. Both these users
+// look for the file in multiple locations. Also see the com.android.tzdata
+// APEX definition.
+
+// The on-device version of the tzdata file in /system/usr/share/zoneinfo/
+// This is the ultimate fallback for bionic for situations where the
+// tzdata APEX is not mounted. For example, bionic in initd. It is also
+// referenced by old copies of bionic that may be statically linked
+// via the NDK. It is no longer used by ZoneInfoDb.
 prebuilt_usr_share {
     name: "tzdata",
     src: "tzdata",
     sub_dir: "zoneinfo",
 }
 
-// A host version of the tzdata module for use by
-// hostdex rules.
-
-// Simulate /system
+// The host version of the tzdata file equivalent to the definition above.
+// Used by bionic on host; bionic is being increasingly used on host for tooling.
 prebuilt_usr_share_host {
     name: "tzdata_host",
     src: "tzdata",