I have tried several times to import Hadoop trunk into Eclipse following the instructions in the BUILDING.txt file, but so far have not been able to get it to work.
If I use a fresh install of Eclipse 4.2.2, Eclipse will complain about an undefined M2_REPO environment variable. I discovered that this is defined automatically by the M2Eclipse plugin, and think that the BUILDING.txt doc should be updated to explain this.
After installing M2Eclipse I tried importing the code again, and now get over 2500 errors related to missing class dependencies. Many of these errors correspond to missing classes in the oah*.proto namespace, which makes me think that 'mvn eclipse:eclipse' is not triggering protoc.