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Zstd: Document update policy

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Add the Zstd update policy to the subtree README.

Also update the documented location of zstd-in.c to match upstream
changes, and normalize naming from 'ZSTD' to 'Zstd'.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Moch <mail@alexmoch.com>
Closes #18089
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Alexander Moch 2026-01-14 10:42:55 +01:00 committed by Brian Behlendorf
parent 2d5a9b6a4c
commit 28291536bc
1 changed files with 31 additions and 13 deletions
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module/zstd/README.md
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@ -1,11 +1,11 @@
# ZSTD-On-ZFS Library Manual
# Zstd-On-ZFS Library Manual
## Introduction
This subtree contains the ZSTD library used in ZFS. It is heavily cut-down by
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.
library, besides upgrading to a newer Zstd release.
Tree structure:
@ -14,25 +14,43 @@ Tree structure:
* `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.
future. Thus we keep them private to Zstd.
## Updating ZSTD
## Zstd update policy
To update ZSTD the following steps need to be taken:
Since the exact compressed byte stream may change between Zstd versions, updates
should follow this policy:
1. Grab the latest release of [ZSTD](https://github.com/facebook/zstd/releases).
1. Zstd may be updated, as needed, after a new .0 release is tagged.
2. Critical patches may be applied up until the next release freeze,
_potentially_ even updating to a newer upstream version.
3. The Zstd version will not be upgraded within a major release.
4. Multiple Zstd versions are not supported concurrently within a release.
5. The library import commit must be a clean, unmodified upstream import. Any
OpenZFS-specific integration or local adjustments go into follow-up commits.
6. Release notes should highlight Zstd updates and any expected impact (e.g.
changes in compression ratio/performance, and differences in compressed byte
streams which may affect deduplication or NOP writes).
## Updating Zstd
To update Zstd the following steps need to be taken:
1. Grab the latest release of [Zstd](https://github.com/facebook/zstd/releases).
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 }'`
```
grep include [path to zstd]/build/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`
5. Follow symbol renaming notes in `include/zstd_compat_wrapper.h`.
## Altering ZSTD and breaking changes
## 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
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
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.