[pnfs] [0/10] Add O_DIRECT support.

[Dean Hildebrand]

This patchset fixes a few bugs and adds O_DIRECT support for pNFS.  Sorry if you receive this twice.

1. 64bit bugfix
2. nfs4-only bugfix
3. Align try_to_commit interface with the other 2 try_to_xxx functions
4. Use enum for result of try_to_xxx funtions
5. Add NFSv41 support for O_DIRECT
6. NFSv4 change to isolate rpc specific code in separate functions.
7. Add direct I/O function to calculate length of i/o.
8. Add pnfs_use_rpc function.  This is needed for O_DIRECT. There are multiple ways this could be done, but since I'm not sure what is involved with doing O_DIRECT support for non-rpc layout drivers, this route seems the simplest for now.
9. Add read O_DIRECT support
10. Add write O_DIRECT support.



Dean