mirror of
https://git.proxmox.com/git/mirror_zfs.git
synced 2024-12-26 03:09:34 +03:00
184df27eef
For Linux, when zfs is compiled as an in kernel static variant and the in kernel zstd library is compiled statically into the kernel a symbol collision will occur. This wrapper header renames all of the relevant zstd functions to avoid this problem. Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Sebastian Gottschall <s.gottschall@dd-wrt.com> Closes #10775
66 lines
2.5 KiB
Markdown
66 lines
2.5 KiB
Markdown
# 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` is the actual `zzstd` kernel module.
|
|
* `lib/` contains the the unmodified, [_"amalgamated"_](https://github.com/facebook/zstd/blob/dev/contrib/single_file_libs/README.md)
|
|
version of the `Zstandard` library, generated from our template file
|
|
* `zstd-in.c` is our template file for generating the 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](https://github.com/facebook/zstd/releases).
|
|
2. Update `module/zstd/zstd-in.c` if required. (see
|
|
`zstd/contrib/single_file_libs/zstd-in.c` in the zstd repository)
|
|
3. Generate the "single-file-library" and put it to `module/zstd/lib/`.
|
|
4. Copy the following files to `module/zstd/lib/`:
|
|
- `zstd/lib/zstd.h`
|
|
- `zstd/lib/common/zstd_errors.h`
|
|
|
|
This can be done using a few shell commands from inside the zfs repo:
|
|
|
|
~~~sh
|
|
cd PATH/TO/ZFS
|
|
|
|
url="https://github.com/facebook/zstd"
|
|
release="$(curl -s "${url}"/releases/latest | grep -oP '(?<=v)[\d\.]+')"
|
|
zstd="/tmp/zstd-${release}/"
|
|
|
|
wget -O /tmp/zstd.tar.gz \
|
|
"${url}/releases/download/v${release}/zstd-${release}.tar.gz"
|
|
tar -C /tmp -xzf /tmp/zstd.tar.gz
|
|
|
|
cp ${zstd}/lib/zstd.h module/zstd/lib/
|
|
cp ${zstd}/lib/zstd_errors.h module/zstd/lib/
|
|
${zstd}/contrib/single_file_libs/combine.sh \
|
|
-r ${zstd}/lib -o module/zstd/lib/zstd.c module/zstd/zstd-in.c
|
|
~~~
|
|
|
|
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: 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.
|