Problem reported by lars_francke on
HDFS-11596. We can no longer easily start a namenode and datanode from the source directory without doing a full build per the wiki instructions: https://wiki.apache.org/hadoop/HowToSetupYourDevelopmentEnvironment
This is because we don't have a top-level dist for HDFS. $HADOOP_YARN_HOME for instance can be set to hadoop-yarn-project/target, but $HADOOP_HDFS_HOME goes into the submodule: hadoop-hdfs-project/hadoop-hdfs/target. This means it's missing the files from the sibling hadoop-hdfs-client module (which is required by the namenode), but also other siblings like nfs and httpfs.
So, I think the right fix is doing the dist stitching at the hadoop-hdfs-project level where we can aggregate all the child modules, and pointing $HADOOP_HDFS_HOME at this directory.