Merge tag 'for-5.5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux

Pull btrfs updates from David Sterba:
 "User visible changes:
   - new block group profiles: RAID1 with 3- and 4- copies
       - RAID1 in btrfs has always 2 copies, now add support for 3 and 4
       - this is an incompat feature (named RAID1C34)
       - recommended use of RAID1C3 is replacement of RAID6 profile on
         metadata, this brings a more reliable resiliency against 2
         device loss/damage

   - support for new checksums
       - per-filesystem, set at mkfs time
       - fast hash (crc32c successor): xxhash, 64bit digest
       - strong hashes (both 256bit): sha256 (slower, FIPS), blake2b
         (faster)
       - the blake2b module goes via the crypto tree, btrfs.ko has a
         soft dependency

   - speed up lseek, don't take inode locks unnecessarily, this can
     speed up parallel SEEK_CUR/SEEK_SET/SEEK_END by 80%

   - send:
       - allow clone operations within the same file
       - limit maximum number of sent clone references to avoid slow
         backref walking

   - error message improvements: device scan prints process name and PID

  Core changes:
   - cleanups
       - remove unique workqueue helpers, used to provide a way to avoid
         deadlocks in the workqueue code, now done in a simpler way
       - remove lots of indirect function calls in compression code
       - extent IO tree code moved out of extent_io.c
       - cleanup backup superblock handling at mount time
       - transaction life cycle documentation and cleanups
       - locking code cleanups, annotations and documentation
       - add more cold, const, pure function attributes
       - removal of unused or redundant struct members or variables

   - new tree-checker sanity tests
       - try to detect missing INODE_ITEM, cross-reference checks of
         DIR_ITEM, DIR_INDEX, INODE_REF, and XATTR_* items

   - remove own bio scheduling code (used to avoid checksum submissions
     being stuck behind other IO), replaced by cgroup controller-based
     code to allow better control and avoid priority inversions in cases
     where the custom and cgroup scheduling disagreed

  Fixes:
   - avoid getting stuck during cyclic writebacks

   - fix trimming of ranges crossing block group boundaries

   - fix rename exchange on subvolumes, all involved subvolumes need to
     be recorded in the transaction"

* tag 'for-5.5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux: (137 commits)
  btrfs: drop bdev argument from submit_extent_page
  btrfs: remove extent_map::bdev
  btrfs: drop bio_set_dev where not needed
  btrfs: get bdev directly from fs_devices in submit_extent_page
  btrfs: record all roots for rename exchange on a subvol
  Btrfs: fix block group remaining RO forever after error during device replace
  btrfs: scrub: Don't check free space before marking a block group RO
  btrfs: change btrfs_fs_devices::rotating to bool
  btrfs: change btrfs_fs_devices::seeding to bool
  btrfs: rename btrfs_block_group_cache
  btrfs: block-group: Reuse the item key from caller of read_one_block_group()
  btrfs: block-group: Refactor btrfs_read_block_groups()
  btrfs: document extent buffer locking
  btrfs: access eb::blocking_writers according to ACCESS_ONCE policies
  btrfs: set blocking_writers directly, no increment or decrement
  btrfs: merge blocking_writers branches in btrfs_tree_read_lock
  btrfs: drop incompat bit for raid1c34 after last block group is gone
  btrfs: add incompat for raid1 with 3, 4 copies
  btrfs: add support for 4-copy replication (raid1c4)
  btrfs: add support for 3-copy replication (raid1c3)
  ...