In this case it could use the Linux crypto API, which already has ZSTD support and provides compress/decompress functions. But that is exported as GPLv2 so ZFS

In this case it could use the Linux crypto API, which already has ZSTD support and provides compress/decompress functions. But that is exported as GPLv2 so ZFS needs to do its own thing. And idk if the API is sufficient w.r.t. to e.g. workspace management/reuse. W.r.t. to ZSTD: The usual thing is to provide a zlib compatible API, which ZSTD does ( https://github.com/facebook/zstd/tree/dev/zlibWrapper https://github.com/facebook/zstd/tree/dev/zlibWrapper ). But the ZSTD zlib compatibility layer causes lower performance, so it is better to use it directly. Maybe all future compression algorithms can provide a ZSTD compatible API, so we have to do less work in the future?