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234e9605c1
It's much nicer to import from upstream this way, and compiles faster too. Everything in lib/ is unmodified 1.4.5. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Rich Ercolani <rincebrain@gmail.com> Closes #12978
48 lines
1.9 KiB
Markdown
48 lines
1.9 KiB
Markdown
# ZSTD-On-ZFS Library Manual
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## Introduction
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This subtree contains the ZSTD library used in ZFS. It is heavily cut-down by
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dropping any unneeded files, and combined into a single file, but otherwise is
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intentionally unmodified. Please do not alter the file containing the zstd
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library, besides upgrading to a newer ZSTD release.
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Tree structure:
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* `zfs_zstd.c` is the actual `zzstd` kernel module.
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* `lib/` contains the unmodified version of the `Zstandard` library
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* `zstd-in.c` is our template file for generating the single-file library
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* `include/`: This directory contains supplemental includes for platform
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compatibility, which are not expected to be used by ZFS elsewhere in the
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future. Thus we keep them private to ZSTD.
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## Updating ZSTD
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To update ZSTD the following steps need to be taken:
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1. Grab the latest release of [ZSTD](https://github.com/facebook/zstd/releases).
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2. Copy the files output by the following script to `module/zstd/lib/`:
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`grep include [path to zstd]/contrib/single_file_libs/zstd-in.c | awk '{ print $2 }'`
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3. Remove debug.c, threading.c, and zstdmt_compress.c.
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4. Update Makefiles with resulting file lists.
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~~~
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Note: if the zstd library for zfs is updated to a newer version,
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the macro list in include/zstd_compat_wrapper.h usually needs to be updated.
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this can be done with some hand crafting of the output of the following
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script (on the object file generated from the "single-file library" script in zstd's
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contrib/single_file_libs):
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`nm zstd.o | awk '{print "#define "$3 " zfs_" $3}' > macrotable`
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## Altering ZSTD and breaking changes
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If ZSTD made changes that break compatibility or you need to make breaking
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changes to the way we handle ZSTD, it is required to maintain backwards
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compatibility.
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We already save the ZSTD version number within the block header to be used
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to add future compatibility checks and/or fixes. However, currently it is
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not actually used in such a way.
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