Inline

[PATCH v4] ceph: Inline data support

This patch implements inline data support for Ceph.

Signed-off-by: Yunchuan Wen <yunchuanwen@ubuntukylin.com>
Signed-off-by: Li Wang <liwang@ubuntukylin.com>

Against v3:
Add the inline switch and make inline size tunable
Improve the back compatibility of mds from (9, 9) to (9, 6), provided the inline
feature is disabled until all mds upgraded to support inline   

Against v2:
Streamline the inline data migration with the subsequent read/write

Against v1:
With simplified process under multiple-writer case,
referred to
http://pad.ceph.com/p/mds-inline-data,
http://www.spinics.net/lists/ceph-devel/msg16018.html