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opnsense-src/sys/contrib/openzfs/module/zstd/README.md
Martin Matuska 716fd348e0 zfs: merge openzfs/zfs@c0cf6ed67 
Notable upstream pull request merges:
  #10662 zvol_wait: Ignore locked zvols
  #12789 Improve log spacemap load time
  #12812 Improved zpool status output, list all affected datasets
  #13277 FreeBSD: Use NDFREE_PNBUF if available
  #13302 Make zfs_max_recordsize default to 16M
  #13311 Fix error handling in FreeBSD's get/putpages VOPs
  #13345 FreeBSD: Fix translation from ABD to physical pages
  #13373 zfs: holds: dequadratify
  #13375 Corrected edge case in uncompressed ARC->L2ARC handling
  #13388 Improve mg_aliquot math
  #13405 Reduce dbuf_find() lock contention
  #13406 FreeBSD: use zero_region instead of allocating a dedicated page

Obtained from:	OpenZFS
OpenZFS commit:	c0cf6ed679
2022-05-19 00:55:59 +02:00

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ZSTD-On-ZFS Library Manual

Introduction

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 are the actual zfs kernel module hooks.
  • 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:

  1. Grab the latest release of ZSTD.
  2. 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.
  5. Follow symbol renaming notes in include/zstd_compat_wrapper.h

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.