This subtree contains the ZSTD library used in ZFS. It is heavily
cut-down by dropping any unneeded files, and combined into a single
file, but otherwise is intentionally unmodified. Please do not alter the
file containing the zstd library, besides upgrading to a newer ZSTD
release.
Tree structure:
zfs_zstd.c is the actual zzstd kernel
module.
lib/ contains the unmodified version of the
Zstandard library
zstd-in.c is our template file for generating the
single-file library
include/: This directory contains supplemental includes
for platform compatibility, which are not expected to be used by ZFS
elsewhere in the future. Thus we keep them private to ZSTD.
Updating ZSTD
To update ZSTD the following steps need to be taken:
Copy the files output by the following script to
module/zstd/lib/:
grep include [path to zstd]/contrib/single_file_libs/zstd-in.c | awk '{ print $2 }'
3. Remove debug.c, threading.c, and zstdmt_compress.c. 4. Update
Makefiles with resulting file lists.
Note: if the zstd library for zfs is updated to a newer version,
the macro list in include/zstd_compat_wrapper.h usually needs to be updated.
this can be done with some hand crafting of the output of the following
script (on the object file generated from the "single-file library" script in zstd's
contrib/single_file_libs):
`nm zstd.o | awk '{print "#define "$3 " zfs_" $3}' > macrotable`
## Altering ZSTD and breaking changes
If ZSTD made changes that break compatibility or you need to make breaking
changes to the way we handle ZSTD, it is required to maintain backwards
compatibility.
We already save the ZSTD version number within the block header to be used
to add future compatibility checks and/or fixes. However, currently it is
not actually used in such a way.
