[DISCUSS] Porting truncate to branch 2.

[Konstantin Shvachko <sh...@gmail.com>]

Hey devs,

This is to discuss whether new truncate feature should be ported to branch
2.
Colin suggested in HDFS-3071 that we merge it in a week or two. Makes sense
to me too.
That way we can get it out in one of the next releases.
Please raise your issues, concerns, or support here.

Do we need to vote on back-porting features from trunk?

There are a few things to complete for truncate. Some already in progress.
And I don't think these should hold the merging of the core feature:
- Add truncate to FileSystem interface and as a new shell command.
HDFS-7057.
- TestCLI for truncate. HDFS-7058.
- Truncate documentation
- Add truncate operation to TestDFSIO and SLive

Thanks,
--Konst