This adds mode argument to nilfs_btnode_submit_block() function and
allows it to issue a read-ahead request.

An optional submit_ptr argument is also added to store the actual
block address for which bio is sent.  submit_ptr is used for a series
of read-ahead requests, and helps to decide if each requested block is
continous to the previous one on disk.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

This removes the obsolete nilfs_btnode_get() function and makes
nilfs_btree_get_block() directly call nilfs_btnode_submit_block().

This expansion will provide better opportunity for code optimization.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

This removes the obsolete argument from nilfs_btnode_submit_block().
This will complete separating a create function of btree node.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

Adds a separate routine for creating a btree node block.  This is a
preparation to reduce the depth of function calls during submitting
btree node buffer.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

Previously, default_backing_dev_info was used for the mapping of btree
node caches.  This uses device dependent backing_dev_info to allow
detailed control of the device for the btree node pages.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

This adds routines for B-tree node buffers.
Signed-off-by: NSeiji Kihara <kihara.seiji@lab.ntt.co.jp>
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>