libbinder: Better oneway function logs.

For manually written/some backends. At least the C++ backend doesn't
pipe oneway errors into libbinder, so won't have the log there yet.

Bug: 160191455
Test: binderLibTest
Change-Id: I96c8b46044e5abc1a61812a998e5fabbb1859984
diff --git a/libs/binder/IPCThreadState.cpp b/libs/binder/IPCThreadState.cpp
index d4c7acf..7d01e0b 100644
--- a/libs/binder/IPCThreadState.cpp
+++ b/libs/binder/IPCThreadState.cpp
@@ -1248,10 +1248,22 @@
                 constexpr uint32_t kForwardReplyFlags = TF_CLEAR_BUF;
                 sendReply(reply, (tr.flags & kForwardReplyFlags));
             } else {
-                if (error != OK || reply.dataSize() != 0) {
-                    alog << "oneway function results will be dropped but finished with status "
-                         << statusToString(error)
-                         << " and parcel size " << reply.dataSize() << endl;
+                if (error != OK) {
+                    alog << "oneway function results for code " << tr.code
+                         << " on binder at "
+                         << reinterpret_cast<void*>(tr.target.ptr)
+                         << " will be dropped but finished with status "
+                         << statusToString(error);
+
+                    // ideally we could log this even when error == OK, but it
+                    // causes too much logspam because some manually-written
+                    // interfaces have clients that call methods which always
+                    // write results, sometimes as oneway methods.
+                    if (reply.dataSize() != 0) {
+                         alog << " and reply parcel size " << reply.dataSize();
+                    }
+
+                    alog << endl;
                 }
                 LOG_ONEWAY("NOT sending reply to %d!", mCallingPid);
             }
diff --git a/libs/binder/tests/binderLibTest.cpp b/libs/binder/tests/binderLibTest.cpp
index 0f7d159..a5261e5 100644
--- a/libs/binder/tests/binderLibTest.cpp
+++ b/libs/binder/tests/binderLibTest.cpp
@@ -404,6 +404,13 @@
     EXPECT_EQ(NO_ERROR, ret);
 }
 
+TEST_F(BinderLibTest, NopTransactionOneway) {
+    status_t ret;
+    Parcel data, reply;
+    ret = m_server->transact(BINDER_LIB_TEST_NOP_TRANSACTION, data, &reply, TF_ONE_WAY);
+    EXPECT_EQ(NO_ERROR, ret);
+}
+
 TEST_F(BinderLibTest, NopTransactionClear) {
     status_t ret;
     Parcel data, reply;
@@ -1182,9 +1189,6 @@
         virtual status_t onTransact(uint32_t code,
                                     const Parcel& data, Parcel* reply,
                                     uint32_t flags = 0) {
-            //printf("%s: code %d\n", __func__, code);
-            (void)flags;
-
             if (getuid() != (uid_t)IPCThreadState::self()->getCallingUid()) {
                 return PERMISSION_DENIED;
             }
@@ -1258,8 +1262,12 @@
                 return NO_ERROR;
             case BINDER_LIB_TEST_NOP_TRANSACTION_WAIT:
                 usleep(5000);
-                return NO_ERROR;
+                [[fallthrough]];
             case BINDER_LIB_TEST_NOP_TRANSACTION:
+                // oneway error codes should be ignored
+                if (flags & TF_ONE_WAY) {
+                    return UNKNOWN_ERROR;
+                }
                 return NO_ERROR;
             case BINDER_LIB_TEST_DELAYED_CALL_BACK: {
                 // Note: this transaction is only designed for use with a