code: private UfsStatus[] getChildrenInUFS(AlluxioURI alluxioUri)
        throws InvalidPathException, IOException {
      MountTable.Resolution resolution = mMountTable.resolve(alluxioUri);
      AlluxioURI ufsUri = resolution.getUri();
      try (CloseableResource<UnderFileSystem> ufsResource = resolution.acquireUfsResource()) {
        UnderFileSystem ufs = ufsResource.get();
        AlluxioURI curUri = ufsUri;
        while (curUri != null) {
          if (mListedDirectories.containsKey(curUri.toString())) {
            List<UfsStatus> childrenList = new ArrayList<>();
            for (UfsStatus childStatus : mListedDirectories.get(curUri.toString())) {
              String childPath = PathUtils.concatPath(curUri, childStatus.getName());
              String prefix = PathUtils.normalizePath(ufsUri.toString(), AlluxioURI.SEPARATOR);
              if (childPath.startsWith(prefix) && childPath.length() > prefix.length()) {
                UfsStatus newStatus = childStatus.copy();
                newStatus.setName(childPath.substring(prefix.length()));
                childrenList.add(newStatus);
              }
            }
            return trimIndirect(childrenList.toArray(new UfsStatus[childrenList.size()]));
          }
          curUri = curUri.getParent();
        }
        UfsStatus[] children =
            ufs.listStatus(ufsUri.toString(), ListOptions.defaults().setRecursive(true));
        // Assumption: multiple mounted UFSs cannot have the same ufsUri
        if (children == null) {
          return EMPTY_CHILDREN;
        }
        mListedDirectories.put(ufsUri.toString(), children);
        return trimIndirect(children);
      }
    }
docs: Get the children in under storage for given alluxio path.
  
  @param alluxioUri alluxio path
  @return the list of children in under storage
  @throws InvalidPathException if aluxioUri is invalid
  @throws IOException if a non-alluxio error occurs