This improves the comments at the top of many functions.  It didn't
dive into the guts of functions because I was trying to
avoid merging problems with the new allocator and back reference work.

extent-tree.c and volumes.c were both skipped, and there is definitely
more work todo in cleaning and commenting the code.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

btrfs_add_leaf_ref was doing checks on the objects it found in the
rbtree to make sure they were properly linked into the tree.  But, the field
it was checking can be safely changed outside of the tree spin lock.

The WARN_ON was for debugging the initial implementation and can be
safely removed.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

btrfs-vol -a /dev/xxx will zero the first and last two MB of the device.
The kernel code needs to wait for this IO to finish before it adds
the device.

btrfs metadata IO does not happen through the block device inode.  A
separate address space is used, allowing the zero filled buffer heads in
the block device inode to be written to disk after FS metadata starts
going down to the disk via the btrfs metadata inode.

The end result is zero filled metadata blocks after adding new devices
into the filesystem.

The fix is a simple filemap_write_and_wait on the block device inode
before actually inserting it into the pool of available devices.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

This patch updates the space balancing code to utilize the new
backref format.  Before, btrfs-vol -b would break any COW links
on data blocks or metadata.  This was slow and caused the amount
of space used to explode if a large number of snapshots were present.

The new code can keeps the sharing of all data extents and
most of the tree blocks.

To maintain the sharing of data extents, the space balance code uses
a seperate inode hold data extent pointers, then updates the references
to point to the new location.

To maintain the sharing of tree blocks, the space balance code uses
reloc trees to relocate tree blocks in reference counted roots.
There is one reloc tree for each subvol, and all reloc trees share
same root key objectid. Reloc trees are snapshots of the latest
committed roots of subvols (root->commit_root).

To relocate a tree block referenced by a subvol, there are two steps.
COW the block through subvol's reloc tree, then update block pointer in
the subvol to point to the new block. Since all reloc trees share
same root key objectid, doing special handing for tree blocks
owned by them is easy. Once a tree block has been COWed in one
reloc tree, we can use the resulting new block directly when the
same block is required to COW again through other reloc trees.
In this way, relocated tree blocks are shared between reloc trees,
so they are also shared between subvols.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

* Add an EXTENT_BOUNDARY state bit to keep the writepage code
from merging data extents that are in the process of being
relocated.  This allows us to do accounting for them properly.

* The balancing code relocates data extents indepdent of the underlying
inode.  The extent_map code was modified to properly account for
things moving around (invalidating extent_map caches in the inode).

* Don't take the drop_mutex in the create_subvol ioctl.  It isn't
required.

* Fix walking of the ordered extent list to avoid races with sys_unlink

* Change the lock ordering rules.  Transaction start goes outside
the drop_mutex.  This allows btrfs_commit_transaction to directly
drop the relocation trees.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Btrfs has a cache of reference counts in leaves, allowing it to
avoid reading tree leaves while deleting snapshots.  To reduce
contention with multiple subvolumes, this cache is private to each
subvolume.

This patch adds shared reference cache support. The new space
balancing code plays with multiple subvols at the same time, So
the old per-subvol reference cache is not well suited.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

* Reserved extent accounting:  reserved extents have been
allocated in the rbtrees that track free space but have not
been allocated on disk.  They were never properly accounted for
in the past, making it hard to know how much space was really free.

* btrfs_find_block_group used to return NULL for block groups that
had been removed by the space balancing code.  This made it hard
to account for space during the final stages of a balance run.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Btrfs metadata writeback is fairly expensive.  Once a tree block is written
it must be cowed before it can be changed again.  The btree writepages
code has a threshold based on a count of dirty btree bytes which is
updated as IO is sent out.

This changes btree_writepages to skip the writeout if there are less
than 32MB of dirty bytes from the btrees, improving performance
across many workloads.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

The code to free block groups needs to drop the space info spin lock
before calling btrfs_remove_free_space_cache (which can schedule).

This is safe because at unmount time, nobody else is going to play
with the block groups.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Btrfs had compatibility code for kernels back to 2.6.18.  These have
been removed, and will be maintained in a separate backport
git tree from now on.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

After a crash, the tree log code uses btrfs_alloc_logged_extent to
record allocations of data extents that it finds in the log tree.  These
come in basically random order, which does not fit how
btrfs_remove_free_space() expects to be called.

btrfs_remove_free_space was changed to support recording an extent
allocation in the middle of a region of free space.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Signed-off-by: Chris Mason <chris.mason@oracle.com>

btrfs had magic to put the chagneset id into a printk on module load.
This removes that from the Makefile and hardcodes the printk to print
"Btrfs"
Signed-off-by: Chris Mason <chris.mason@oracle.com>

The code to update the on disk i_size happens before the
ordered_extent record is removed.  So, it is possible for multiple
ordered_extent completion routines to run at the same time, and to
find each other in the ordered tree.

The end result is they both decide not to update disk_i_size, leaving
it too small.  This temporary fix just puts the updates inside
the extent_mutex.  A real solution would be stronger ordering of
disk_i_size updates against removing the ordered extent from the tree.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

This patch makes the back reference system to explicit record the
location of parent node for all types of extents. The location of
parent node is placed into the offset field of backref key. Every
time a tree block is balanced, the back references for the affected
lower level extents are updated.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Tree log blocks are only reserved, and should not ever get fully
allocated on disk.  This check makes sure they stay out of the
extent tree.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Tree blocks were using async bio submission, but the sum was still
being done directly during writepage.  This moves the checksumming
into the worker thread.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1) replace the per fs_info extent_io_tree that tracked free space with two
rb-trees per block group to track free space areas via offset and size.  The
reason to do this is because most allocations come with a hint byte where to
start, so we can usually find a chunk of free space at that hint byte to satisfy
the allocation and get good space packing.  If we cannot find free space at or
after the given offset we fall back on looking for a chunk of the given size as
close to that given offset as possible.  When we fall back on the size search we
also try to find a slot as close to the size we want as possible, to avoid
breaking small chunks off of huge areas if possible.

2) remove the extent_io_tree that tracked the block group cache from fs_info and
replaced it with an rb-tree thats tracks block group cache via offset.  also
added a per space_info list that tracks the block group cache for the particular
space so we can lookup related block groups easily.

3) cleaned up the allocation code to make it a little easier to read and a
little less complicated.  Basically there are 3 steps, first look from our
provided hint.  If we couldn't find from that given hint, start back at our
original search start and look for space from there.  If that fails try to
allocate space if we can and start looking again.  If not we're screwed and need
to start over again.

4) small fixes.  there were some issues in volumes.c where we wouldn't allocate
the rest of the disk.  fixed cow_file_range to actually pass the alloc_hint,
which has helped a good bit in making the fs_mark test I run have semi-normal
results as we run out of space.  Generally with data allocations we don't track
where we last allocated from, so everytime we did a data allocation we'd search
through every block group that we have looking for free space.  Now searching a
block group with no free space isn't terribly time consuming, it was causing a
slight degradation as we got more data block groups.  The alloc_hint has fixed
this slight degredation and made things semi-normal.

There is still one nagging problem I'm working on where we will get ENOSPC when
there is definitely plenty of space.  This only happens with metadata
allocations, and only when we are almost full.  So you generally hit the 85%
mark first, but sometimes you'll hit the BUG before you hit the 85% wall.  I'm
still tracking it down, but until then this seems to be pretty stable and make a
significant performance gain.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

cache block group had a few bugs in the error handling code,
this makes sure paths get properly released and the correct return value
goes out.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

It was incorrectly adding an extra sizeof(struct btrfs_item) and causing
false positives (oops)
Signed-off-by: Chris Mason <chris.mason@oracle.com>

I had incorrectly disabled the check for the block number being correct
in the header block.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

More testing has turned up a bug, disable this for now.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

This is the same way the transaction code makes sure that all the
other tree blocks are safely on disk.  There's an extent_io tree
for each root, and any blocks allocated to the tree logs are
recorded in that tree.

At tree-log sync, the extent_io tree is walked to flush down the
dirty pages and wait for them.

The main benefit is less time spent walking the tree log and skipping
clean pages, and getting sequential IO down to the drive.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

This changes the log tree copy code to use btrfs_insert_items and
to work in larger batches where possible.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Since tree log blocks get freed every transaction, they never really
need to be written to disk.  This skips the step where we update
metadata to record they were allocated.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Signed-off-by: Chris Mason <chris.mason@oracle.com>

Drop i_mutex during the commit

Don't bother doing the fsync at all unless the dir is marked as dirtied
and needing fsync in this transaction.  For directories, this means
that someone has unlinked a file from the dir without fsyncing the
file.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Signed-off-by: Chris Mason <chris.mason@oracle.com>

Signed-off-by: Chris Mason <chris.mason@oracle.com>

* Pin down data blocks to prevent them from being reallocated like so:

trans 1: allocate file extent
trans 2: free file extent
trans 3: free file extent during old snapshot deletion
trans 3: allocate file extent to new file
trans 3: fsync new file

Before the tree logging code, this was legal because the fsync
would commit the transation that did the final data extent free
and the transaction that allocated the extent to the new file
at the same time.

With the tree logging code, the tree log subtransaction can commit
before the transaction that freed the extent.  If we crash,
we're left with two different files using the extent.

* Don't wait in start_transaction if log replay is going on.  This
avoids deadlocks from iput while we're cleaning up link counts in the
replay code.

* Don't deadlock in replay_one_name by trying to read an inode off
the disk while holding paths for the directory

* Hold the buffer lock while we mark a buffer as written.  This
closes a race where someone is changing a buffer while we write it.
They are supposed to mark it dirty again after they change it, but
this violates the cow rules.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

---
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Orphan items use BTRFS_ORPHAN_OBJECTID (-5UUL) as key objectid. This
affects the find free objectid functions, inode objectid can easily
overflow after orphan file cleanup.

---
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Fix a bunch of trivial sparse complaints.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

btrfs_ilookup is unused, which is good because a normal filesystem
should never have to use ilookup anyway.  Remove it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Add two missing endianess conversions in this function, found by sparse.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

d_obtain_alias is intended as a tailcall that can pass in errors encoded
in the inode pointer if needed, so use it that way instead of
duplicating the error handling.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Signed-off-by: Chris Mason <chris.mason@oracle.com>

File syncs and directory syncs are optimized by copying their
items into a special (copy-on-write) log tree.  There is one log tree per
subvolume and the btrfs super block points to a tree of log tree roots.

After a crash, items are copied out of the log tree and back into the
subvolume.  See tree-log.c for all the details.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Signed-off-by: Chris Mason <chris.mason@oracle.com>