btrfs: make subpage handling be feature full

[CHANGLOG]
v1:
- Merge previous two patches into one
- Re-order the patches so preparation/fixes are always before feature
  enablement
- Update the commit message of the first patch
  So that we do not focus on the out-of-tree part, but explain why it's
  not ideal in the first place (double page zeroing), and just mention
  the behavior change in the future.

Since the introduction of btrfs subapge support in v5.15, there are
quite some limitations:

- No RAID56 support
  Added in v5.19.

- No memory efficient scrub support
  Added in v6.4.

- No block perfect compressed write support
  Previously btrfs requires the dirty range to be fully page aligned, or
  it will skip compression completely.

  Added in v6.13.

- Various subpage related error handling fixes
  Added in v6.14.

- No support to create inline data extent
- No partial uptodate page support
  This is a long existing optimization supported by EXT4/XFS and
  is required to pass generic/563 with subpage block size.

The last two are addressed in this patchset.

And since all features are implemented for subpage cases, the long
existing experimental warning message can be dropped, as it is already
causing a lot of concerns for users who checks the dmesg carefully.

Qu Wenruo (7):
  btrfs: prevent inline data extents read from touching blocks beyond
    its range
  btrfs: fix the qgroup data free range for inline data extents
  btrfs: introduce a read path dedicated extent lock helper
  btrfs: make btrfs_do_readpage() to do block-by-block read
  btrfs: allow buffered write to avoid full page read if it's block
    aligned
  btrfs: allow inline data extents creation if block size < page size
  btrfs: remove the subpage related warning message

 fs/btrfs/defrag.c       |   2 +-
 fs/btrfs/direct-io.c    |   2 +-
 fs/btrfs/disk-io.c      |   5 -
 fs/btrfs/extent_io.c    | 224 +++++++++++++++++++++++++++++++++++-----
 fs/btrfs/file.c         |   9 +-
 fs/btrfs/inode.c        |  34 +++---
 fs/btrfs/ordered-data.c |  29 ++++--
 fs/btrfs/ordered-data.h |   3 +-
 8 files changed, 239 insertions(+), 69 deletions(-)

-- 
2.48.1