When syncing the log, if we fail to write log tree extent buffers, we mark
the log for a full commit and abort the transaction. However we don't need
to abort the transaction, all we really need to do is to make sure no one
can commit a superblock pointing to new log tree roots. Just because we
got a failure writing extent buffers for a log tree, it does not mean we
will also fail to do a transaction commit.

One particular case is if due to a bug somewhere, when writing log tree
extent buffers, the tree checker detects some corruption and the writeout
fails because of that. Aborting the transaction can be very disruptive for
a user, specially if the issue happened on a root filesystem. One example
is the scenario in the Link tag below, where an isolated corruption on log
tree leaves was causing transaction aborts when syncing the log.

Link: https://lore.kernel.org/linux-btrfs/ae169fc6-f504-28f0-a098-6fa6a4dfb612@leemhuis.info/
CC: stable@vger.kernel.org # 5.15+
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Signed-off-by: NFilipe Manana <fdmanana@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

[BUG]
Even with commit 81d5d614 ("btrfs: enhance unsupported compat RO
flags handling"), btrfs can still mount a fs with unsupported compat_ro
flags read-only, then remount it RW:

  # btrfs ins dump-super /dev/loop0 | grep compat_ro_flags -A 3
  compat_ro_flags		0x403
			( FREE_SPACE_TREE |
			  FREE_SPACE_TREE_VALID |
			  unknown flag: 0x400 )

  # mount /dev/loop0 /mnt/btrfs
  mount: /mnt/btrfs: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error.
         dmesg(1) may have more information after failed mount system call.
  ^^^ RW mount failed as expected ^^^

  # dmesg -t | tail -n5
  loop0: detected capacity change from 0 to 1048576
  BTRFS: device fsid cb5b82f5-0fdd-4d81-9b4b-78533c324afa devid 1 transid 7 /dev/loop0 scanned by mount (1146)
  BTRFS info (device loop0): using crc32c (crc32c-intel) checksum algorithm
  BTRFS info (device loop0): using free space tree
  BTRFS error (device loop0): cannot mount read-write because of unknown compat_ro features (0x403)
  BTRFS error (device loop0): open_ctree failed

  # mount /dev/loop0 -o ro /mnt/btrfs
  # mount -o remount,rw /mnt/btrfs
  ^^^ RW remount succeeded unexpectedly ^^^

[CAUSE]
Currently we use btrfs_check_features() to check compat_ro flags against
our current mount flags.

That function get reused between open_ctree() and btrfs_remount().

But for btrfs_remount(), the super block we passed in still has the old
mount flags, thus btrfs_check_features() still believes we're mounting
read-only.

[FIX]
Replace the existing @sb argument with @is_rw_mount.

As originally we only use @sb to determine if the mount is RW.

Now it's callers' responsibility to determine if the mount is RW, and
since there are only two callers, the check is pretty simple:

- caller in open_ctree()
  Just pass !sb_rdonly().

- caller in btrfs_remount()
  Pass !(*flags & SB_RDONLY), as our check should be against the new
  flags.

Now we can correctly reject the RW remount:

  # mount /dev/loop0 -o ro /mnt/btrfs
  # mount -o remount,rw /mnt/btrfs
  mount: /mnt/btrfs: mount point not mounted or bad option.
         dmesg(1) may have more information after failed mount system call.
  # dmesg -t | tail -n 1
  BTRFS error (device loop0: state M): cannot mount read-write because of unknown compat_ro features (0x403)
Reported-by: NChung-Chiang Cheng <shepjeng@gmail.com>
Fixes: 81d5d614 ("btrfs: enhance unsupported compat RO flags handling")
CC: stable@vger.kernel.org # 5.15+
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

From a recent regression report, we found that after commit 947a6299
("btrfs: move tree block parentness check into
validate_extent_buffer()") if we have a level mismatch (false alert
though), there is no error message at all.

This makes later debugging harder.  This patch will add the proper error
message for such case.

Link: https://lore.kernel.org/linux-btrfs/CABXGCsNzVxo4iq-tJSGm_kO1UggHXgq6CdcHDL=z5FL4njYXSQ@mail.gmail.com/Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

repair_io_failure ties directly into all the glory low-level details of
mapping a bio with a logic address to the actual physical location.
Move it right below btrfs_submit_bio to keep all the related logic
together.

Also move btrfs_repair_eb_io_failure to its caller in disk-io.c now that
repair_io_failure is available in a header.
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The code used by btrfs_submit_bio only interacts with the rest of
volumes.c through __btrfs_map_block (which itself is a more generic
version of two exported helpers) and does not really have anything
to do with volumes.c.  Create a new bio.c file and a bio.h header
going along with it for the btrfs_bio-based storage layer, which
will grow even more going forward.

Also update the file with my copyright notice given that a large
part of the moved code was written or rewritten by me.
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

[BUG]
If dev-replace failed to re-construct its data/metadata, the kernel
message would be incorrect for the missing device:

 BTRFS info (device dm-1): dev_replace from <missing disk> (devid 2) to /dev/mapper/test-scratch2 started
 BTRFS error (device dm-1): failed to rebuild valid logical 38862848 for dev (efault)

Note the above "dev (efault)" of the second line.
While the first line is properly reporting "<missing disk>".

[CAUSE]
Although dev-replace is using btrfs_dev_name(), the heavy lifting work
is still done by scrub (scrub is reused by both dev-replace and regular
scrub).

Unfortunately scrub code never uses btrfs_dev_name() helper, as it's
only declared locally inside dev-replace.c.

[FIX]
Fix the output by:

- Move the btrfs_dev_name() helper to volumes.h

- Use btrfs_dev_name() to replace open-coded rcu_str_deref() calls
  Only zoned code is not touched, as I'm not familiar with degraded
  zoned code.

- Constify return value and parameter

Now the output looks pretty sane:

 BTRFS info (device dm-1): dev_replace from <missing disk> (devid 2) to /dev/mapper/test-scratch2 started
 BTRFS error (device dm-1): failed to rebuild valid logical 38862848 for dev <missing disk>
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

[BACKGROUND]
Although both btrfs metadata and data has their read time verification
done at endio time (btrfs_validate_metadata_buffer() and
btrfs_verify_data_csum()), metadata has extra verification, mostly
parentness check including first key/transid/owner_root/level, done at
read_tree_block() and btrfs_read_extent_buffer().

On the other hand, all the data verification is done at endio context.

[ENHANCEMENT]
This patch will make a new union in btrfs_bio, taking the space of the
old data checksums, thus it will not increase the memory usage.

With that extra btrfs_tree_parent_check inside btrfs_bio, we can just
pass the check parameter into read_extent_buffer_pages(), and before
submitting the bio, we can copy the check structure into btrfs_bio.

And finally at endio time, we can grab btrfs_bio::parent_check and pass
it to validate_extent_buffer(), to move the remaining checks into it.

This brings the following benefits:

- Much simpler btrfs_read_extent_buffer()
  Now it only needs to iterate through all mirrors.

- Simpler read-time transid check
  Previously we go verify_parent_transid() after reading out the extent
  buffer.
  Now the transid check is done inside the endio function, no other
  code can modify the content.
  Thus no need to use the extent lock anymore.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

There are several different tree block parentness check parameters used
across several helpers:

- level
  Mandatory

- transid
  Under most cases it's mandatory, but there are several backref cases
  which skips this check.

- owner_root
- first_key
  Utilized by most top-down tree search routine. Otherwise can be
  skipped.

Those four members are not always mandatory checks, and some of them are
the same u64, which means if some arguments got swapped compiler will
not catch it.

Furthermore if we're going to further expand the parentness check, we
need to modify quite some helpers just to add one more parameter.

This patch will concentrate all these members into a structure called
btrfs_tree_parent_check, and pass that structure for the following
helpers:

- btrfs_read_extent_buffer()
- read_tree_block()
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

All callers except one pass NULL, so the parameter can be dropped and
the inode::io_tree initialization can be open coded.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The function is for internal interfaces so we should use the
btrfs_inode.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The function is for internal interfaces so we should use the
btrfs_inode.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The function is for internal interfaces so we should use the
btrfs_inode.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The function is for internal interfaces so we should use the
btrfs_inode.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The async bio submit is for internal interfaces so we should use the
btrfs_inode.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

After previous patches the unused parameters can be removed from
btree_submit_bio_start and btrfs_submit_bio_start as they don't need to
conform to the extent_submit_bio_start_t typedef.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

There's a callback function parameter for btrfs_wq_submit_bio that can
be one of: metadata, buffered data, direct io data. The callback
abstraction is unnecessary as we have all functions available.

Replace the parameter with a command that leads to a direct call in
run_one_async_start. The called functions can be then simplified and we
can also remove the extent_submit_bio_start_t typedef.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Since we have switched all raid56 workload to submit-and-wait method,
there is no use for btrfs_fs_info::endio_raid56_workers workqueue and
btrfs_raid_bio::end_io_work.

Remove them to save some memory.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Move these out of ctree.h into super.h to cut down on code in ctree.h.
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Move these out of ctree.h into scrub.h to cut down on code in ctree.h.
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Move these out of ctree.h into relocation.h to cut down on code in
ctree.h
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Move these out of ctree.h into uuid-tree.h to cut down on the code in
ctree.h.
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Now that the defrag code is all in one file, create a defrag.h and move
all the defrag related prototypes and helper out of ctree.h and into
defrag.h.
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Move all the root-tree.c prototypes to root-tree.h, and then update all
the necessary files to include the new header.
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Move all the extent tree related prototypes to extent-tree.h out of
ctree.h, and then go include it everywhere needed so everything
compiles.
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

This is a large patch, but because they're all macros it's impossible to
split up.  Simply copy all of the item accessors in ctree.h and paste
them in accessors.h, and then update any files to include the header so
everything compiles.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
[ reformat comments, style fixups ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Now that we're not using this code anywhere we can remove it as well as
the member from fs_info.

We don't have any mount options or on/off features that would utilize
the pending infrastructure, the last one was inode_cache.
There was a patchset [1] to enable some features from sysfs that would
break things if it would be set immediately. In case we'll need that
kind of logic again the patch can be reverted, but for the current use
it can be replaced by the single state bit to do the commit.

[1] https://lore.kernel.org/linux-btrfs/1422609654-19519-1-git-send-email-quwenruo@cn.fujitsu.com/Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
[ add note ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

We have several fs wide related helpers in ctree.h.  The bulk of these
are the incompat flag test helpers, but there are things such as
btrfs_fs_closing() and the read only helpers that also aren't directly
related to the ctree code.  Move these into a fs.h header, which will
serve as the location for file system wide related helpers.
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

There's a request to automatically enable async discard for capable
devices. We can do that, the async mode is designed to wait for larger
freed extents and is not intrusive, with limits to iops, kbps or latency.

The status and tunables will be exported in /sys/fs/btrfs/FSID/discard .

The automatic selection is done if there's at least one discard capable
device in the filesystem (not capable devices are skipped). Mounting
with any other discard option will honor that option, notably mounting
with nodiscard will keep it disabled.

Link: https://lore.kernel.org/linux-btrfs/CAEg-Je_b1YtdsCR0zS5XZ_SbvJgN70ezwvRwLiCZgDGLbeMB=w@mail.gmail.com/Reviewed-by: NBoris Burkov <boris@bur.io>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

This inline helper calls btrfs_fs_compat_ro(), which is defined in
another header.  To avoid weird header dependency problems move this
helper into disk-io.c with the rest of the global root helpers.
Reviewed-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Since leaf is already NULL, and no other branch will go to fail_unlock,
the fail_unlock label is useless and can be removed
Signed-off-by: NPeng Hao <flyingpeng@tencent.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

When performing seeding on a zoned filesystem it is necessary to
initialize each zoned device's btrfs_zoned_device_info structure,
otherwise mounting the filesystem will cause a NULL pointer dereference.

This was uncovered by fstests' testcase btrfs/163.

CC: stable@vger.kernel.org # 5.15+
Signed-off-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Previous commit a05d3c91 ("btrfs: check superblock to ensure the fs
was not modified at thaw time") only checks the content of the super
block, but it doesn't really check if the on-disk super block has a
matching checksum.

This patch will add the checksum verification to thaw time superblock
verification.

This involves the following extra changes:

- Export btrfs_check_super_csum()
  As we need to call it in super.c.

- Change the argument list of btrfs_check_super_csum()
  Instead of passing a char *, directly pass struct btrfs_super_block *
  pointer.

- Verify that our checksum type didn't change before checking the
  checksum value, like it's done at mount time

Fixes: a05d3c91 ("btrfs: check superblock to ensure the fs was not modified at thaw time")
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

[BUG]
When one user did a wrong attempt to clear block group tree, which can
not be done through mount option, by using "-o clear_cache,space_cache=v2",
it will cause the following error on a fs with block-group-tree feature:

  BTRFS info (device dm-1): force clearing of disk cache
  BTRFS info (device dm-1): using free space tree
  BTRFS info (device dm-1): clearing free space tree
  BTRFS info (device dm-1): clearing compat-ro feature flag for FREE_SPACE_TREE (0x1)
  BTRFS info (device dm-1): clearing compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)
  BTRFS error (device dm-1): block-group-tree feature requires fres-space-tree and no-holes
  BTRFS error (device dm-1): super block corruption detected before writing it to disk
  BTRFS: error (device dm-1) in write_all_supers:4318: errno=-117 Filesystem corrupted (unexpected superblock corruption detected)
  BTRFS warning (device dm-1: state E): Skipping commit of aborted transaction.

[CAUSE]
Although the dependency for block-group-tree feature is just an
artificial one (to reduce test matrix), we put the dependency check into
btrfs_validate_super().

This is too strict, and during space cache clearing, we will have a
window where free space tree is cleared, and we need to commit the super
block.

In that window, we had block group tree without v2 cache, and triggered
the artificial dependency check.

This is not necessary at all, especially for such a soft dependency.

[FIX]
Introduce a new helper, btrfs_check_features(), to do all the runtime
limitation checks, including:

- Unsupported incompat flags check

- Unsupported compat RO flags check

- Setting missing incompat flags

- Artificial feature dependency checks
  Currently only block group tree will rely on this.

- Subpage runtime check for v1 cache

With this helper, we can move quite some checks from
open_ctree()/btrfs_remount() into it, and just call it after
btrfs_parse_options().

Now "-o clear_cache,space_cache=v2" will not trigger the above error
anymore.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
[ edit messages ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

This exists to insert the btree_inode in the super blocks inode hash
table.  Since it's only used for the btree inode move the code to where
we use it in disk-io.c and remove the helper.
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

We only use this for normal inodes, so don't set it if we're not a
normal inode.
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Since commit 78361f64ff42 ("btrfs: remove unnecessary EXTENT_UPTODATE
state in buffered I/O path") we no longer check ->track_uptodate, remove
it.
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

We have two variants of lock/unlock extent, one set that takes a cached
state, another that does not.  This is slightly annoying, and generally
speaking there are only a few places where we don't have a cached state.
Simplify this by making lock_extent/unlock_extent the only variant and
make it take a cached state, then convert all the callers appropriately.
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Btrfs qgroup has a long history of bringing performance penalty in
btrfs_commit_transaction().

Although we tried our best to migrate such impact, there is still an
unsolved call site, btrfs_drop_snapshot().

This function will find the highest shared tree block and modify its
extent ownership to do a subvolume/snapshot dropping.

Such change will affect the whole subtree, and cause tons of qgroup
dirty extents and stall btrfs_commit_transaction().

To avoid such problem, here we introduce a new sysfs interface,
/sys/fs/btrfs/<uuid>/qgroups/drop_subptree_threshold, to determine at
whether and at which level we should skip qgroup accounting for subtree
dropping.

The default value is BTRFS_MAX_LEVEL, thus every subtree drop will go
through qgroup accounting, to ensure qgroup numbers are kept as
consistent as possible.

While for performance sensitive cases, add a way to change the values to
more reasonable values like 3, to make any subtree, which is at or higher
than level 3, to mark qgroup inconsistent and skip the accounting.

The cost is obvious, the qgroup number is no longer consistent, but at
least performance is more reasonable, and users have the control.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The problem of long mount time caused by block group item search is
already known for some time, and the solution of block group tree has
been proposed.

There is really no need to bound this feature into extent tree v2, just
introduce compat RO flag, BLOCK_GROUP_TREE, to correctly solve the
problem.

All the code handling block group root is already in the upstream
kernel, thus this patch really only needs to introduce the new compat RO
flag.

This patch introduces one extra artificial limitation on block group
tree feature, that free space cache v2 and no-holes feature must be
enabled to use this new compat RO feature.

This artificial requirement is mostly to reduce the test combinations,
and can be a guideline for future features, to mostly rely on the latest
default features.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The extent tree v2 needs a new root for storing all block group items,
the whole feature hasn't been finished yet so we can afford to do some
changes.

My initial proposal years ago just added a new tree rootid, and load it
from tree root, just like what we did for quota/free space tree/uuid/extent
roots.

But the extent tree v2 patches introduced a completely new way to store
block group tree root into super block which is arguably wasteful.

Currently there are only 3 trees stored in super blocks, and they all
have their valid reasons:

- Chunk root
  Needed for bootstrap.

- Tree root
  Really the entry point for all trees.

- Log root
  This is special as log root has to be updated out of existing
  transaction mechanism.

There is not even any reason to put block group root into super blocks,
the block group tree is updated at the same time as the old extent tree,
no need for extra bootstrap/out-of-transaction update.

So just move block group root from super block into tree root.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>