VFS fileop cleanups by collapsing AIO and vector IO

Hi Andrew,

Here is the updated set of patches for 2.6.17-rc6-mm2 with
autofs fixes. I made the series against latest -mm since, 
there are bunch of tweaks needed to suite -mm (xfs, ecryptfs, 
reiser4 etc). If you prefer against mainline (2.6.17-rc6) and 
want to merge yourself, let me know - I can post that set as well.

===========

These series of patches clean up and streamlines generic_file_*
interfaces in filemap.c.

First (3) patches collapses all the vectored IO support into
single set of file-operation method using aio_read/aio_write.
This work was originally suggested & started by Christoph Hellwig,
when Zach Brown tried to add vectored support for AIO.

Patch 4, sets all the filesystems .read/.write/.aio_read/.aio_write
methods correctly to allow us to cleanup most generic_file_*_read/write
interfaces in filemap.c

After this patch set, we should end up with ONLY following
read/write (exported) interfaces in filemap.c:

        generic_file_aio_read() - read handler
        generic_file_aio_write() - write handler
        generic_file_aio_write_nolock() - no lock write handler

Here is the summary:

[PATCH 1/4] Vectorize aio_read/aio_write methods

[PATCH 2/4] Remove readv/writev methods and use aio_read/aio_write
instead.

[PATCH 3/4] Core aio changes to support vectored AIO.

[PATCH 4/4] Streamline generic_file_* interfaces and filemap cleanups

BTW, Chuck Lever is actually re-arranging NFS DIO, AIO code to
fit into this model.


Thanks,
Badari