I agree with Suresh and Jing that DFSConfigKeys is not a public API so that it should not be used outside HDFS. On the other hand, the conf property key is a public API. For example,
public static final String DFS_BLOCK_SIZE_KEY = "dfs.blocksize";
DFS_BLOCK_SIZE_KEY is not a public API. Projects outside HDFS should not use DFSConfigKeys.DFS_BLOCK_SIZE_KEY. However, the value "dfs.blocksize" is a public API as it is defined in hdfs-default.xml.
In the long term, Slider should eliminate referencing DFSConfigKeys. In the short term, I don't mind adding back the previously removed constants as deprecated. Sounds good?