In blocklayout driver. There are two things happening
while layoutcommit/cleanup.
1. the modified extents are encoded.
2. On cleanup the extents are put back on the layout rw
   extents list, for reads.

In the new system where actual xdr encoding is done in
encode_layoutcommit() directly into xdr buffer, these are
the new commit stages:

1. On setup_layoutcommit, the range is adjusted as before
   and a structure is allocated for communication with
   bl_encode_layoutcommit && bl_cleanup_layoutcommit
   (Generic layer provides a void-star to hang it on)

2. bl_encode_layoutcommit is called to do the actual
   encoding directly into xdr. The commit-extent-list is not
   freed and is stored on above structure.
   FIXME: The code is not yet converted to the new XDR cleanup

3. On cleanup the commit-extent-list is put back by a call
   to set_to_rw() as before, but with no need for XDR decoding
   of the list as before. And the commit-extent-list is freed.
   Finally allocated structure is freed.

[rm inode and pnfs_layout_hdr args from cleanup_layoutcommit()]
Signed-off-by: NJim Rees <rees@umich.edu>
[pnfsblock: introduce bl_committing list]
Signed-off-by: NPeng Tao <peng_tao@emc.com>
[pnfsblock: SQUASHME: adjust to API change]
Signed-off-by: NFred Isaman <iisaman@citi.umich.edu>
[blocklayout: encode_layoutcommit implementation]
Signed-off-by: NBoaz Harrosh <bharrosh@panasas.com>
[pnfsblock: fix bug setting up layoutcommit.]
Signed-off-by: NTao Guo <guotao@nrchpc.ac.cn>
[pnfsblock: cleanup_layoutcommit wants a status parameter]
Signed-off-by: NBoaz Harrosh <bharrosh@panasas.com>
Signed-off-by: NBenny Halevy <bhalevy@panasas.com>
Signed-off-by: NBenny Halevy <bhalevy@tonian.com>
Signed-off-by: NJim Rees <rees@umich.edu>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>