This patch try CoW support for a refcounted record.

the whole process will be:
1. Calculate how many clusters we need to CoW and where we start.
   Extents that are not completely encompassed by the write will
   be broken on 1MB boundaries.
2. Do CoW for the clusters with the help of page cache.
3. Change the b-tree structure with the new allocated clusters.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

Add 'Decrement refcount for delete' in to the normal truncate
process. So for a refcounted extent record, call refcount rec
decrementation instead of cluster free.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

Add function ocfs2_mark_extent_refcounted which can mark
an extent refcounted.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

    Given a physical cpos and length, decrement the refcount
in the tree. If the refcount for any portion of the extent goes
to zero, that portion is queued for freeing.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

    Given a physical cpos and length, increment the refcount
in the tree. If the extent has not been seen before, a refcount
record is created for it. Refcount records may be merged or
split by this operation.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

Now fs/ocfs2/alloc.c has more than 7000 lines. It contains our
basic b-tree operation. Although we have already make our b-tree
operation generic, the basic structrue ocfs2_path which is used
to iterate one b-tree branch is still static and limited to only
used in alloc.c. As refcount tree need them and I don't want to
add any more b-tree unrelated code to alloc.c, export them out.

Signed-off-by: Tao Ma <tao.ma@oracle.com> 

Add refcount b-tree as a new extent tree so that it can
use the b-tree to store and maniuplate ocfs2_refcount_rec.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

ocfs2_mark_extent_written actually does the following things:
1. check the parameters.
2. initialize the left_path and split_rec.
3. call __ocfs2_mark_extent_written. it will do:
   1) check the flags of unwritten
   2) do the real split work.
The whole process is packed tightly somehow. So this patch
will abstract 2 different functions so that future b-tree
operation can work with it.

1. __ocfs2_split_extent will accept path and split_rec and do
  the real split work.
2. ocfs2_change_extent_flag will accept a new flag and initialize
   path and split_rec.

So now ocfs2_mark_extent_written will do:
1. check the parameters.
2. call ocfs2_change_extent_flag.
   1) initalize the left_path and split_rec.
   2) check whether the new flags conflict with the old one.
   3) call __ocfs2_split_extent to do the split.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

Add a new operation eo_ocfs2_extent_contig int the extent tree's
operations vector. So that with the new refcount tree, We want
this so that refcount trees can always return CONTIG_NONE and
prevent extent merging.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

Add basic refcount tree root operation.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

Implement locking around struct ocfs2_refcount_tree.  This protects
all read/write operations on refcount trees.  ocfs2_refcount_tree
has its own lock and its own caching_info, protecting buffers among
multiple nodes.

User must call ocfs2_lock_refcount_tree before his operation on
the tree and unlock it after that.

ocfs2_refcount_trees are referenced by the block number of the
refcount tree root block, So we create an rb-tree on the ocfs2_super
to look them up.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

refcount tree should use its own caching info so that when
we downconvert the refcount tree lock, we can drop all the
cached buffer head.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

refcount tree lock resource is used to protect refcount
tree read/write among multiple nodes.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

In meta downconvert, we need to checkpoint the metadata in an inode.
For refcount tree, we also need it. So abstract the process out.

Signed-off-by: Tao Ma <tao.ma@oracle.com> 

Signed-off-by: Tao Ma <tao.ma@oracle.com>

Add metaecc and journal trigger for ocfs2_refcount_block.
Signed-off-by: Tao Ma <tao.ma@oracle.com>

Signed-off-by: Tao Ma <tao.ma@oracle.com>

With this commit, extent tree operations are divorced from inodes and
rely on ocfs2_caching_info.  Phew!
Signed-off-by: Joel Becker <joel.becker@oracle.com>

We only allow unwritten extents on data, so the toplevel
ocfs2_mark_extent_written() can use an inode all it wants.  But the
subfunction isn't even using the inode argument.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

Don't use a struct inode anymore.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

It already has an extent_tree.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

One more generic btree function that is isolated from struct inode.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

One more function that doesn't need a struct inode to pass to its
children.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

One more function down, no inode in the entire insert-extent chain.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

ocfs2_insert_extent() wants to insert a record into the extent map if
it's an inode data extent.  But since many btrees can call that
function, let's make it an op on ocfs2_extent_tree.  Other tree types
can leave it empty.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

It's not using it, so remove it from the parameter list.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

It already has an ocfs2_extent_tree and doesn't need the inode.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

We don't want struct inode in generic btree operations.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

Don't pass the inode in.  We don't want it around for generic btree
operations.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

They aren't using it, so remove it from their parameter lists.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

Another on the way to generic btree functions.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

Give it an ocfs2_extent_tree and it is happy.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

ocfs2_remove_extent() wants to truncate the extent map if it's
truncating an inode data extent.  But since many btrees can call that
function, let's make it an op on ocfs2_extent_tree.  Other tree types
can leave it empty.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

It's not using it anymore.  Remove it from the parameter list.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

ocfs2_grow_branch() not really using it other than to pass it to the
subfunctions ocfs2_shift_tree_depth(), ocfs2_find_branch_target(), and
ocfs2_add_branch().  The first two weren't it either, so they drop the
argument.  ocfs2_add_branch() only passed it to
ocfs2_adjust_rightmost_branch(), which drops the inode argument and uses
the ocfs2_extent_tree as well.

ocfs2_append_rec_to_path() can be take an ocfs2_extent_tree instead of
the inode.  The function ocfs2_adjust_rightmost_records() goes along for
the ride.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

It's not using it, so remove it from the parameter list.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

Drop it from the parameters - they already have ocfs2_extent_list.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

It already gets ocfs2_extent_tree, so we can just use that.  This chains
to the same modification for ocfs2_remove_rightmost_path() and
ocfs2_rotate_rightmost_leaf_left().
Signed-off-by: Joel Becker <joel.becker@oracle.com>

It already has struct ocfs2_extent_tree, which has the caching info.  So
we don't need to pass it struct inode.
Signed-off-by: Joel Becker <joel.becker@oracle.com>

It already has struct ocfs2_extent_tree, which has the caching info.  So
we don't need to pass it struct inode.
Signed-off-by: Joel Becker <joel.becker@oracle.com>