Btrfs: [PATCH] extent_map: provide generic bmap

generic_bmap is completely trivial, while the extent to bh mapping in
btrfs is rather complex.  So provide a extent_bmap instead that takes
a get_extent callback and can be used by filesystem using the extent_map
code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --cc fs/btrfs/extent_map.c
Simple merge

diff --cc fs/btrfs/extent_map.h
Simple merge

diff --cc fs/btrfs/inode.c
Simple merge