Current refcounttree codes actually didn't writeback the new pages out in
write-back mode, due to a bug of always passing a ZERO number of clusters
to 'ocfs2_cow_sync_writeback', the patch tries to pass a proper one in.
Signed-off-by: NTristan Ye <tristan.ye@oracle.com>
Cc: stable@kernel.org
Signed-off-by: NJoel Becker <jlbec@evilplan.org>

This patch change mutex_lock to a new subclass and
add a new inode lock subclass for the target inode
which caused this lockdep warning.

=============================================
[ INFO: possible recursive locking detected ]
2.6.35+ #5
---------------------------------------------
reflink/11086 is trying to acquire lock:
 (Meta){+++++.}, at: [<ffffffffa06f9d65>] ocfs2_reflink_ioctl+0x898/0x1229 [ocfs2]

but task is already holding lock:
 (Meta){+++++.}, at: [<ffffffffa06f9aa0>] ocfs2_reflink_ioctl+0x5d3/0x1229 [ocfs2]

other info that might help us debug this:
6 locks held by reflink/11086:
 #0:  (&sb->s_type->i_mutex_key#15/1){+.+.+.}, at: [<ffffffff820e09ec>] lookup_create+0x26/0x97
 #1:  (&sb->s_type->i_mutex_key#15){+.+.+.}, at: [<ffffffffa06f99a0>] ocfs2_reflink_ioctl+0x4d3/0x1229 [ocfs2]
 #2:  (Meta){+++++.}, at: [<ffffffffa06f9aa0>] ocfs2_reflink_ioctl+0x5d3/0x1229 [ocfs2]
 #3:  (&oi->ip_xattr_sem){+.+.+.}, at: [<ffffffffa06f9b58>] ocfs2_reflink_ioctl+0x68b/0x1229 [ocfs2]
 #4:  (&oi->ip_alloc_sem){+.+.+.}, at: [<ffffffffa06f9b67>] ocfs2_reflink_ioctl+0x69a/0x1229 [ocfs2]
 #5:  (&sb->s_type->i_mutex_key#15/2){+.+...}, at: [<ffffffffa06f9d4f>] ocfs2_reflink_ioctl+0x882/0x1229 [ocfs2]

stack backtrace:
Pid: 11086, comm: reflink Not tainted 2.6.35+ #5
Call Trace:
 [<ffffffff82063dd9>] validate_chain+0x56e/0xd68
 [<ffffffff82062275>] ? mark_held_locks+0x49/0x69
 [<ffffffff82064d6d>] __lock_acquire+0x79a/0x7f1
 [<ffffffff82065a81>] lock_acquire+0xc6/0xed
 [<ffffffffa06f9d65>] ? ocfs2_reflink_ioctl+0x898/0x1229 [ocfs2]
 [<ffffffffa06c9ade>] __ocfs2_cluster_lock+0x975/0xa0d [ocfs2]
 [<ffffffffa06f9d65>] ? ocfs2_reflink_ioctl+0x898/0x1229 [ocfs2]
 [<ffffffffa06e107b>] ? ocfs2_wait_for_recovery+0x15/0x8a [ocfs2]
 [<ffffffffa06cb6ea>] ocfs2_inode_lock_full_nested+0x1ac/0xdc5 [ocfs2]
 [<ffffffffa06f9d65>] ? ocfs2_reflink_ioctl+0x898/0x1229 [ocfs2]
 [<ffffffff820623a0>] ? trace_hardirqs_on_caller+0x10b/0x12f
 [<ffffffff82060193>] ? debug_mutex_free_waiter+0x4f/0x53
 [<ffffffffa06f9d65>] ocfs2_reflink_ioctl+0x898/0x1229 [ocfs2]
 [<ffffffffa06ce24a>] ? ocfs2_file_lock_res_init+0x66/0x78 [ocfs2]
 [<ffffffff820bb2d2>] ? might_fault+0x40/0x8d
 [<ffffffffa06df9f6>] ocfs2_ioctl+0x61a/0x656 [ocfs2]
 [<ffffffff820ee5d3>] ? mntput_no_expire+0x1d/0xb0
 [<ffffffff820e07b3>] ? path_put+0x2c/0x31
 [<ffffffff820e53ac>] vfs_ioctl+0x2a/0x9d
 [<ffffffff820e5903>] do_vfs_ioctl+0x45d/0x4ae
 [<ffffffff8233a7f6>] ? _raw_spin_unlock+0x26/0x2a
 [<ffffffff8200299c>] ? sysret_check+0x27/0x62
 [<ffffffff820e59ab>] sys_ioctl+0x57/0x7a
 [<ffffffff8200296b>] system_call_fastpath+0x16/0x1b
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

We cannot call grab_cache_page() when holding filesystem locks or with
a transaction started as grab_cache_page() calls page allocation with
GFP_KERNEL flag and thus page reclaim can recurse back into the filesystem
causing deadlocks or various assertion failures. We have to use
find_or_create_page() instead and pass it GFP_NOFS as we do with other
allocations.
Acked-by: NMark Fasheh <mfasheh@suse.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NTao Ma <tao.ma@oracle.com>

In CoW, when we meet with a readahead page, we know
it is time to move the readahead window. So carry
out a new readahead.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

Add a new function ocfs2_readahead_for_cow so that
we start readahead before we start our CoW.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

Add a new parameter 'struct file *' to ocfs2_refcount_cow
so that we can add readahead support later.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

The refcount record calculation in ocfs2_calc_refcount_meta_credits
is too optimistic that we can always allocate contiguous clusters
and handle an already existed refcount rec as a whole. Actually
because of file system fragmentation, we may have the chance to split
a refcount record into 3 parts during the transaction. So consider
the worst case in record calculation.

Cc: stable@kernel.org
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

During CoW, the pages after i_size don't contain valid data, so there's
no need to read and duplicate them.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

ocfs2's allocation unit is the cluster.  This can be larger than a block
or even a memory page.  This means that a file may have many blocks in
its last extent that are beyond the block containing i_size.  There also
may be more unwritten extents after that.

When ocfs2 grows a file, it zeros the entire cluster in order to ensure
future i_size growth will see cleared blocks.  Unfortunately,
block_write_full_page() drops the pages past i_size.  This means that
ocfs2 is actually leaking garbage data into the tail end of that last
cluster.  This is a bug.

We adjust ocfs2_write_begin_nolock() and ocfs2_extend_file() to detect
when a write or truncate is past i_size.  They will use
ocfs2_zero_extend() to ensure the data is properly zeroed.

Older versions of ocfs2_zero_extend() simply zeroed every block between
i_size and the zeroing position.  This presumes three things:

1) There is allocation for all of these blocks.
2) The extents are not unwritten.
3) The extents are not refcounted.

(1) and (2) hold true for non-sparse filesystems, which used to be the
only users of ocfs2_zero_extend().  (3) is another bug.

Since we're now using ocfs2_zero_extend() for sparse filesystems as
well, we teach ocfs2_zero_extend() to check every extent between
i_size and the zeroing position.  If the extent is unwritten, it is
ignored.  If it is refcounted, it is CoWed.  Then it is zeroed.
Signed-off-by: NJoel Becker <joel.becker@oracle.com>
Cc: stable@kernel.org

Truncate is just a special case of punching holes(from new i_size to
end), we therefore could take advantage of the existing
ocfs2_remove_btree_range() to reduce the comlexity and redundancy in
alloc.c.  The goal here is to make truncate more generic and
straightforward.

Several functions only used by ocfs2_commit_truncate() will smiply be
removed.

ocfs2_remove_btree_range() was originally used by the hole punching
code, which didn't take refcount trees into account (definitely a bug).
We therefore need to change that func a bit to handle refcount trees.
It must take the refcount lock, calculate and reserve blocks for
refcount tree changes, and decrease refcounts at the end.  We replace 
ocfs2_lock_allocators() here by adding a new func
ocfs2_reserve_blocks_for_rec_trunc() which accepts some extra blocks to
reserve.  This will not hurt any other code using
ocfs2_remove_btree_range() (such as dir truncate and hole punching).

I merged the following steps into one patch since they may be
logically doing one thing, though I know it looks a little bit fat
to review.

1). Remove redundant code used by ocfs2_commit_truncate(), since we're
    moving to ocfs2_remove_btree_range anyway.

2). Add a new func ocfs2_reserve_blocks_for_rec_trunc() for purpose of
    accepting some extra blocks to reserve.

3). Change ocfs2_prepare_refcount_change_for_del() a bit to fit our
    needs.  It's safe to do this since it's only being called by
    truncate.

4). Change ocfs2_remove_btree_range() a bit to take refcount case into
    account.

5). Finally, we change ocfs2_commit_truncate() to call
    ocfs2_remove_btree_range() in a proper way.

The patch has been tested normally for sanity check, stress tests
with heavier workload will be expected.

Based on this patch, fixing the punching holes bug will be fairly easy.
Signed-off-by: NTristan Ye <tristan.ye@oracle.com>
Acked-by: NMark Fasheh <mfasheh@suse.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

In ocfs2, we use ocfs2_extend_trans() to extend a journal handle's
blocks. But if jbd2_journal_extend() fails, it will only restart
with the the new number of blocks.  This tends to be awkward since
in most cases we want additional reserved blocks. It makes our code
harder to mantain since the caller can't be sure all the original
blocks will not be accessed and dirtied again.  There are 15 callers
of ocfs2_extend_trans() in fs/ocfs2, and 12 of them have to add
h_buffer_credits before they call ocfs2_extend_trans().  This makes
ocfs2_extend_trans() really extend atop the original block count.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

jbd[2]_journal_dirty_metadata() only returns 0.  It's been returning 0
since before the kernel moved to git.  There is no point in checking
this error.

ocfs2_journal_dirty() has been faithfully returning the status since the
beginning.  All over ocfs2, we have blocks of code checking this can't
fail status.  In the past few years, we've tried to avoid adding these
checks, because they are pointless.  But anyone who looks at our code
assumes they are needed.

Finally, ocfs2_journal_dirty() is made a void function.  All error
checking is removed from other files.  We'll BUG_ON() the status of
jbd2_journal_dirty_metadata() just in case they change it someday.  They
won't.
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

In reflink we update the id info on the disk but forgot to update
the corresponding information in the VFS inode.  Update them
accordingly when we want to preserve the attributes.
Reported-by: NJeff Liu <jeff.liu@oracle.com>
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Cc: <stable@kernel.org>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h

percpu.h is included by sched.h and module.h and thus ends up being
included when building most .c files.  percpu.h includes slab.h which
in turn includes gfp.h making everything defined by the two files
universally available and complicating inclusion dependencies.

percpu.h -> slab.h dependency is about to be removed.  Prepare for
this change by updating users of gfp and slab facilities include those
headers directly instead of assuming availability.  As this conversion
needs to touch large number of source files, the following script is
used as the basis of conversion.

  http://userweb.kernel.org/~tj/misc/slabh-sweep.py

The script does the followings.

* Scan files for gfp and slab usages and update includes such that
  only the necessary includes are there.  ie. if only gfp is used,
  gfp.h, if slab is used, slab.h.

* When the script inserts a new include, it looks at the include
  blocks and try to put the new include such that its order conforms
  to its surrounding.  It's put in the include block which contains
  core kernel includes, in the same order that the rest are ordered -
  alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
  doesn't seem to be any matching order.

* If the script can't find a place to put a new include (mostly
  because the file doesn't have fitting include block), it prints out
  an error message indicating which .h file needs to be added to the
  file.

The conversion was done in the following steps.

1. The initial automatic conversion of all .c files updated slightly
   over 4000 files, deleting around 700 includes and adding ~480 gfp.h
   and ~3000 slab.h inclusions.  The script emitted errors for ~400
   files.

2. Each error was manually checked.  Some didn't need the inclusion,
   some needed manual addition while adding it to implementation .h or
   embedding .c file was more appropriate for others.  This step added
   inclusions to around 150 files.

3. The script was run again and the output was compared to the edits
   from #2 to make sure no file was left behind.

4. Several build tests were done and a couple of problems were fixed.
   e.g. lib/decompress_*.c used malloc/free() wrappers around slab
   APIs requiring slab.h to be added manually.

5. The script was run on all .h files but without automatically
   editing them as sprinkling gfp.h and slab.h inclusions around .h
   files could easily lead to inclusion dependency hell.  Most gfp.h
   inclusion directives were ignored as stuff from gfp.h was usually
   wildly available and often used in preprocessor macros.  Each
   slab.h inclusion directive was examined and added manually as
   necessary.

6. percpu.h was updated not to include slab.h.

7. Build test were done on the following configurations and failures
   were fixed.  CONFIG_GCOV_KERNEL was turned off for all tests (as my
   distributed build env didn't work with gcov compiles) and a few
   more options had to be turned off depending on archs to make things
   build (like ipr on powerpc/64 which failed due to missing writeq).

   * x86 and x86_64 UP and SMP allmodconfig and a custom test config.
   * powerpc and powerpc64 SMP allmodconfig
   * sparc and sparc64 SMP allmodconfig
   * ia64 SMP allmodconfig
   * s390 SMP allmodconfig
   * alpha SMP allmodconfig
   * um on x86_64 SMP allmodconfig

8. percpu.h modifications were reverted so that it could be applied as
   a separate patch and serve as bisection point.

Given the fact that I had only a couple of failures from tests on step
6, I'm fairly confident about the coverage of this conversion patch.
If there is a breakage, it's likely to be something in one of the arch
headers which should be easily discoverable easily on most builds of
the specific arch.
Signed-off-by: NTejun Heo <tj@kernel.org>
Guess-its-ok-by: NChristoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>

In case the block we are going to free is allocated from
a discontiguous block group, we have to use suballoc_loc
to be the right group.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

Get the suballoc_loc from ocfs2_claim_new_inode() or
ocfs2_claim_metadata().  Store it on the appropriate field of the block
we just allocated.
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

They all take an ocfs2_alloc_context, which has the allocation inode.
Signed-off-by: NJoel Becker <joel.becker@oracle.com>
Signed-off-by: NTao Ma <tao.ma@oracle.com>

In reflink, we need to upate i_blocks for the target inode.
Reported-by: NJie Liu <jeff.liu@oracle.com>
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

Get rid of the initialize dquot operation - it is now always called from
the filesystem and if a filesystem really needs it's own (which none
currently does) it can just call into it's own routine directly.

Rename the now static low-level dquot_initialize helper to __dquot_initialize
and vfs_dq_init to dquot_initialize to have a consistent namespace.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJan Kara <jack@suse.cz>

This patch add extent block (metadata) stealing mechanism for
extent allocation. This mechanism is same as the inode stealing.
if no room in slot specific extent_alloc, we will try to
allocate extent block from the next slot.
Signed-off-by: NTiger Yang <tiger.yang@oracle.com>
Acked-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

In CoW, we have to make sure that the page is already written
out to the disk. So we have a BUG_ON(PageDirty(page)).

In ppc platform we have pagesize=64K, so if the cs=4K, if the
file have fragmented clusters, we will map the page many times.
See this file as an example.
Tree Depth: 0   Count: 19   Next Free Rec: 14
	## Offset        Clusters       Block#          Flags
	0  0             4              2164864         0x2 Refcounted
	1  4             2              9302792         0x2 Refcounted
...

We have to replace the extent recs one by one, so the page with index 0
will be mapped and dirtied twice.

I'd like to leave the BUG_ON there while adding a check so that in
case we meet with an error in other platforms, we can find it easily.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

In ocfs2_duplicate_clusters_by_page, we calculate map_end
by shifting page_index. But actually in case we meet with
a large offset(say in a i686 box, poff_t is only 32 bits
and page_index=2056240), we will overflow. So change the
type of page_index to loff_t.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

That is "success", "unknown", "through", "performance", "[re|un]mapping"
, "access", "default", "reasonable", "[con]currently", "temperature"
, "channel", "[un]used", "application", "example","hierarchy", "therefore"
, "[over|under]flow", "contiguous", "threshold", "enough" and others.
Signed-off-by: NAndré Goddard Rosa <andre.goddard@gmail.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

sparse check finds some endian problem and some other minor issues.
There is an obsolete function which should be removed.
So this patch resolve all these.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

ocfs2 refcount tree is stored as an extent tree while
the leaf ocfs2_refcount_rec points to a refcount block.

The following step can trip a kernel panic.
mkfs.ocfs2 -b 512 -C 1M --fs-features=refcount $DEVICE
mount -t ocfs2 $DEVICE $MNT_DIR
FILE_NAME=$RANDOM
FILE_NAME_1=$RANDOM
FILE_REF="${FILE_NAME}_ref"
FILE_REF_1="${FILE_NAME}_ref_1"
for((i=0;i<305;i++))
do
# /mnt/1048576 is a file with 1048576 sizes.
cat /mnt/1048576 >> $MNT_DIR/$FILE_NAME
cat /mnt/1048576 >> $MNT_DIR/$FILE_NAME_1
done
for((i=0;i<3;i++))
do
cat /mnt/1048576 >> $MNT_DIR/$FILE_NAME
done

for((i=0;i<2;i++))
do
cat /mnt/1048576 >> $MNT_DIR/$FILE_NAME
cat /mnt/1048576 >> $MNT_DIR/$FILE_NAME_1
done

cat /mnt/1048576 >> $MNT_DIR/$FILE_NAME

for((i=0;i<11;i++))
do
cat /mnt/1048576 >> $MNT_DIR/$FILE_NAME
cat /mnt/1048576 >> $MNT_DIR/$FILE_NAME_1
done
reflink $MNT_DIR/$FILE_NAME $MNT_DIR/$FILE_REF
# write_f is a program which will write some bytes to a file at offset.
# write_f -f file_name -l offset -w write_bytes.
./write_f -f $MNT_DIR/$FILE_REF -l $[310*1048576] -w 4096
./write_f -f $MNT_DIR/$FILE_REF -l $[306*1048576] -w 4096
./write_f -f $MNT_DIR/$FILE_REF -l $[311*1048576] -w 4096
./write_f -f $MNT_DIR/$FILE_NAME -l $[310*1048576] -w 4096
./write_f -f $MNT_DIR/$FILE_NAME -l $[311*1048576] -w 4096
reflink $MNT_DIR/$FILE_NAME $MNT_DIR/$FILE_REF_1
./write_f -f $MNT_DIR/$FILE_NAME -l $[311*1048576] -w 4096
#kernel panic here.

The reason is that if the ocfs2_extent_rec is the last record
in a leaf extent block, the old solution fails to find the
suitable end cpos. So this patch try to walk through the b-tree,
find the next sub root and get the c_pos the next sub-tree starts
from.

btw, I have runned tristan's test case against the patched kernel
for several days and this type of kernel panic never happens again.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

The old reflink fails to handle inodes with inline data and will oops
if it encounters them.  This patch copies inline data to the new inode.
Extended attributes may still be refcounted.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>
Tested-by: NTristan Ye <tristan.ye@oracle.com>

As its name ocfs2_complete_reflink indicates, it should
be called after all the work for reflink is done, so
it really should be called after we reflink xattr
successfully.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>
Tested-by: NTristan Ye <tristan.ye@oracle.com>

The ioctl will take 3 parameters: old_path, new_path and
preserve and call vfs_reflink. It is useful when we backport
reflink features to old kernels.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

Implement ocfs2_reflink.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

reflink has 2 options for the destination file:
1. snapshot: reflink will attempt to preserve ownership, permissions,
   and all other security state in order to create a full snapshot.
2. new file: it will acquire the data extent sharing but will see the
   file's security state and attributes initialized as a new file.

So add the option to ocfs2.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

Actually the whole reflink will touch refcount tree 2 times:
1. It will add the clusters in the extent record to the tree if it
   isn't refcounted before.
2. It will add 1 refcount to these clusters when it add these
   extent records to the tree.

So actually we shouldn't do merge in the 1st operation since the 2nd
one will soon be called and we may have to split it again. Do a merge
first and split soon is a waste of time. So we only merge in the 2nd
round. This is done by adding a new internal __ocfs2_increase_refcount
and call it with "not-merge" for 1st refcount operation in reflink.

This also has a side-effect that we don't need to worry too much about
the metadata allocation in the 2nd round since it will only merge and
no split will happen for those records.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

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

Now with xattr refcount support, we need to check whether
we have xattr refcounted before we remove the refcount tree.

Now the mechanism is:
1) Check whether i_clusters == 0, if no, exit.
2) check whether we have i_xattr_loc in dinode. if yes, exit.
2) Check whether we have inline xattr stored outside, if yes, exit.
4) Remove the tree.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

In ocfs2, when xattr's value is larger than OCFS2_XATTR_INLINE_SIZE,
it will be kept outside of the blocks we store xattr entry. And they
are stored in a b-tree also. So this patch try to attach all these
clusters to refcount tree also.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

In order to make 2 transcation(xattr and cow) independent with each other,
we CoW the whole xattr out in case we are setting them.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

We currently use pagecache to duplicate clusters in CoW,
but it isn't suitable for xattr case. So abstract it out
so that the caller can decide which method it use.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

A reflink creates a snapshot of a file, that means the attributes
must be identical except for three exceptions - nlink, ino, and ctime.

As for time changes, Here is a brief description:

1. Source file:
   1) atime: Ignore. Let the lazy atime code handle that.
   2) mtime: don't touch.
   3) ctime: If we change the tree (adding REFCOUNTED to at least one
             extent), update it.
2. Destination file:
   1) atime: ignore.
   2) mtime: we want it to appear identical to the source.
   3) ctime: update.

The idea here is that an ls -l will show the same time for the
src and target - it shows mtime.  Backup software like rsync and tar
will treat the new file correctly too.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

2 major functions are added in this patch.

ocfs2_attach_refcount_tree will create a new refcount tree to the
old file if it doesn't have one and insert all the extent records
to the tree if they are not refcounted.

ocfs2_create_reflink_node will:
1. set the refcount tree to the new file.
2. call ocfs2_duplicate_extent_list which will iterate all the
   extents for the old file, insert it to the new file and increase
   the corresponding referennce count.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

When we truncate a file to a specific size which resides in a reflinked
cluster, we need to CoW it since ocfs2_zero_range_for_truncate will
zero the space after the size(just another type of write).

So we add a "max_cpos" in ocfs2_refcount_cow so that it will stop when
it hit the max cluster offset.
Signed-off-by: NTao Ma <tao.ma@oracle.com>

During CoW, if the old extent record is refcounted, we allocate
som new clusters and do CoW. Actually we can have some improvement
here. If the old extent has refcount=1, that means now it is only
used by this file. So we don't need to allocate new clusters, just
remove the refcounted flag and it is OK. We also have to remove
it from the refcount tree while not deleting it.
Signed-off-by: NTao Ma <tao.ma@oracle.com>