Merge git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable

Merge git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable

* git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable: (864 commits)
  Btrfs: explicitly mark the tree log root for writeback
  Btrfs: Drop the hardware crc32c asm code
  Btrfs: Add Documentation/filesystem/btrfs.txt, remove old COPYING
  Btrfs: kmap_atomic(KM_USER0) is safe for btrfs_readpage_end_io_hook
  Btrfs: Don't use kmap_atomic(..., KM_IRQ0) during checksum verifies
  Btrfs: tree logging checksum fixes
  Btrfs: don't change file extent's ram_bytes in btrfs_drop_extents
  Btrfs: Use btrfs_join_transaction to avoid deadlocks during snapshot creation
  Btrfs: drop remaining LINUX_KERNEL_VERSION checks and compat code
  Btrfs: drop EXPORT symbols from extent_io.c
  Btrfs: Fix checkpatch.pl warnings
  Btrfs: Fix free block discard calls down to the block layer
  Btrfs: avoid orphan inode caused by log replay
  Btrfs: avoid potential super block corruption
  Btrfs: do not call kfree if kmalloc failed in btrfs_sysfs_add_super
  Btrfs: fix a memory leak in btrfs_get_sb
  Btrfs: Fix typo in clear_state_cb
  Btrfs: Fix memset length in btrfs_file_write
  Btrfs: update directory's size when creating subvol/snapshot
  Btrfs: add permission checks to the ioctls
  ...