[PATCH v2 0/4] erofs: introduce on-disk compression configurations

[Gao Xiang via Linux-erofs <linux-erofs@lists.ozlabs.org>]

From: Gao Xiang <hsiangkao@redhat.com>

Hi folks,

When we provides support for different algorithms or big pcluster, it'd
be necessary to record some configuration in the per-fs basis.

For example, when big pcluster feature for lz4 is enabled, we need to
know the largest pclustersize in the whole fs instance to adjust per-CPU
buffers in advance, which will be used to handle in-place decompression
failure for inplace IO then. And we also need to record global arguments
(e.g. dict_size) for the upcoming LZMA algorithm support.

Therefore, this patchset introduces a new INCOMPAT feature called
COMPR_CFGS, which provides an available algorithm bitmap in the sb
and a variable array list to store corresponding arguments for each
available algorithms.

Since such a INCOMPAT sb feature will be introduced, it'd be better to
reuse such bit for BIGPCLUSTER feature as well since BIGPCLUSTER feature
depends on COMPR_CFGS and will be released together with COMPR_CFGS.

If COMPR_CFGS is disabled, the field of available algorithm bitmap would
become a lz4_max_distance (which is now reserved as 0), and max_distance
can be safely ignored for old kernels since 64k lz4 dictionary is always
enough even new images could reduce the sliding window.

Thanks,
Gao Xiang

Changes since v1:
 - [2/4] add a comment on lz4_max_distance (Chao);
 - [4/4] fix a misplaced label (Chao);
 - [4/4] enable COMPR_CFGS with BIG_PCLUSTER later since they share
         the same bit.

Gao Xiang (3):
  erofs: introduce erofs_sb_has_xxx() helpers
  erofs: introduce on-disk lz4 fs configurations
  erofs: add on-disk compression configurations

Huang Jianan (1):
  erofs: support adjust lz4 history window size

 fs/erofs/decompressor.c |  35 ++++++++--
 fs/erofs/erofs_fs.h     |  20 +++++-
 fs/erofs/internal.h     |  33 +++++++++
 fs/erofs/super.c        | 147 +++++++++++++++++++++++++++++++++++++++-
 4 files changed, 224 insertions(+), 11 deletions(-)

-- 
2.20.1