Fix kernel bug in INIT_LX_SIZE

https://moodle-app2.let.ethz.ch/mod/forum/discuss.php?d=100480

lib/aos/aos_rpc.c

@@ -126,34 +126,78 @@ aos_rpc_serial_putchar(struct aos_rpc *rpc, char c) {
     );
 }
 
-// putchar for terminal printing is too slow so we send buffers instead
+// putchar for terminal printing is too slow so we write buffers instead
-errval_t
+// the corresponding interface does not know about errors, just partial writes
+size_t
 aos_rpc_serial_write(struct aos_rpc *rpc, const char *buf, size_t buf_len) {
     errval_t err;
 
     // split the buffer into chunks for sending
+    size_t total_bytes = 0;
     while(buf_len > 0) {
-        size_t chunk_len = buf_len;
+        size_t chunk_len = MIN(buf_len, RPC_SHARED_SIZE);
-        if (chunk_len > RPC_SHARED_SIZE) {
-            chunk_len = RPC_SHARED_SIZE;
-        }
 
         memcpy(rpc->shared_mem, buf, chunk_len);
 
+        size_t written_bytes;
         err = do_aos_rpc(
             rpc, RPC_MTYPE_SERIAL_WRITE,
             NULL_CAP, chunk_len, 0, 0,
-            NULL, NULL, NULL, NULL
+            NULL, NULL, &written_bytes, NULL
         );
         if (err_is_fail(err)) {
-            return err;
+            return total_bytes;
+        }
+
+        total_bytes += written_bytes;
+
+        // if the receiver was not able to write all we have given, return for now
+        if (written_bytes < chunk_len) {
+            return total_bytes;
         }
 
         buf += chunk_len;
         buf_len -= chunk_len;
     }
 
-    return SYS_ERR_OK;
+    return total_bytes;
+}
+
+// getchar for terminal reading is too slow so we read buffers instead
+// the corresponding interface does not know about errors, just partial reads
+size_t
+aos_rpc_serial_read(struct aos_rpc *rpc, const char *buf, size_t buf_len) {
+    errval_t err;
+
+    // split the buffer into chunks for reading
+    size_t total_bytes = 0;
+    while(buf_len > 0) {
+        size_t chunk_len = MIN(buf_len, RPC_SHARED_SIZE);
+
+        memcpy(rpc->shared_mem, buf, chunk_len);
+
+        size_t written_bytes;
+        err = do_aos_rpc(
+            rpc, RPC_MTYPE_SERIAL_WRITE,
+            NULL_CAP, chunk_len, 0, 0,
+            NULL, NULL, &written_bytes, NULL
+        );
+        if (err_is_fail(err)) {
+            return total_bytes;
+        }
+
+        total_bytes += written_bytes;
+
+        // if the receiver was not able to write all we have given, return for now
+        if (written_bytes < chunk_len) {
+            return total_bytes;
+        }
+
+        buf += chunk_len;
+        buf_len -= chunk_len;
+    }
+
+    return total_bytes;
 }
 
 errval_t