btrfs: introduce a new experimental feature, RAID56_VSL

The new feature stands for RAID56 Variable Stripe Length, however the VSL part is not implemented yet, thus the whole feature is still hidden behind experimental, and there are definitely works left to properly split the 1st patch.

But for now, this series can pass most fstests cases.
The failing ones are all related to mixed block groups, which can not be created nor mounted with this new feature.

The roadmap for the full RAID56 VSL implementation is split into two parts:

- Introduce a new datasize member
This series.

An fs with data_size 8K and sectorsize 4K will act like a fs with sectorsize 8K.
Meaning the minimal write size is 8K for data.

However the checksum is still calculated based sectorsize, meanwhile we can still recover each corrupted 4K sector inside a 8K data block.

The idea and implementation is not that complex, we're just reusing the existing bs > ps support to handle it (on 4K page sized systems).

But the challenge is the details where some part of the code still requires sectorsize (checksum related), meanwhile every other location goes datasize for data.

- Introduce a new RAID56_VSL chunk type
It will have the following requirements:

* Can have up to (datasize / sectorsize) data stripes

* The number of data stripes are always power of 2 This is only for every RAID56_VSL chunk, users can still have whatever number of devices in the fs.

* The full stripe length is always datasize

This allows every data write to be full stripe aligned. And for read repair/scrub, we can still locate and recover a single sector inside a RAID56 stripe.

This is less flex than the traditional RAID56, which has no limit on the number of data stripes, but has the write-hole problem. And will require users to determine the maximum device numbers at mkfs time, without any way to change to another datasize.

But the second part is pretty easy to implement.

As the digest shows, the biggest problem is the first patch, which is touching over 200 sectorsize users, and is definitely the source of all bugs I hit and fixed so far.

If anyone has a better way to address the rename, I'm all ears.

Qu Wenruo (2):
btrfs: split sectorsize into datasize and sectorsize
btrfs: implement a new incompat feature, raid56_vsl

 fs/btrfs/accessors.h                   |   2 +
 fs/btrfs/bio.c                         |  16 +++-
 fs/btrfs/block-group.c                 |   2 +-
 fs/btrfs/btrfs_inode.h                 |  10 +++
 fs/btrfs/compression.c                 |  12 +--
 fs/btrfs/defrag.c                      |  14 +--
 fs/btrfs/delalloc-space.c              |  22 ++---
 fs/btrfs/direct-io.c                   |   6 +-
 fs/btrfs/disk-io.c                     |  43 +++++++---
 fs/btrfs/extent-io-tree.c              |   2 +-
 fs/btrfs/extent-tree.c                 |   4 +-
 fs/btrfs/extent_io.c                   |  62 +++++++-------
 fs/btrfs/extent_map.c                  |   2 +-
 fs/btrfs/fiemap.c                      |   2 +-
 fs/btrfs/file-item.c                   |  22 +++--
 fs/btrfs/file.c                        |  72 ++++++++--------
 fs/btrfs/fs.h                          |  27 ++++--
 fs/btrfs/inode-item.c                  |   6 +-
 fs/btrfs/inode.c                       | 113 +++++++++++++------------
 fs/btrfs/ioctl.c                       |  12 +--
 fs/btrfs/lzo.c                         |  14 +--
 fs/btrfs/reflink.c                     |  16 ++--
 fs/btrfs/relocation.c                  |  16 ++--
 fs/btrfs/send.c                        |   4 +-
 fs/btrfs/subpage.c                     |  96 +++++++++++++++------
 fs/btrfs/subpage.h                     |   2 +-
 fs/btrfs/super.c                       |   8 +-
 fs/btrfs/sysfs.c                       |   8 +-
 fs/btrfs/tests/btrfs-tests.c           |   6 +-
 fs/btrfs/tests/free-space-tree-tests.c |   2 +-
 fs/btrfs/tree-checker.c                |   2 +-
 fs/btrfs/tree-log.c                    |   6 +-
 fs/btrfs/volumes.c                     |   2 +-
 fs/btrfs/zlib.c                        |   6 +-
 fs/btrfs/zoned.c                       |   4 +-
 fs/btrfs/zstd.c                        |   8 +-
 include/uapi/linux/btrfs.h             |  22 +++++
 include/uapi/linux/btrfs_tree.h        |   3 +-
 38 files changed, 403 insertions(+), 273 deletions(-)

2.55.0