nilfs2: fiemap support

This adds fiemap to nilfs.  Two new functions, nilfs_fiemap and
nilfs_find_uncommitted_extent are added.

nilfs_fiemap() implements the fiemap inode operation, and
nilfs_find_uncommitted_extent() helps to get a range of data blocks
whose physical location has not been determined.

nilfs_fiemap() collects extent information by looping through
nilfs_bmap_lookup_contig and nilfs_find_uncommitted_extent routines.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c
index c9a30d7..2f560c9 100644
--- a/fs/nilfs2/file.c
+++ b/fs/nilfs2/file.c
@@ -155,6 +155,7 @@
 	.truncate	= nilfs_truncate,
 	.setattr	= nilfs_setattr,
 	.permission     = nilfs_permission,
+	.fiemap		= nilfs_fiemap,
 };
 
 /* end of file */