Is the Solaris Porting Layer really due to a licensing issue or just a ZFS portability issue? FreeBSD's ZFS implementation reportedly has a similar portability shim.¹ The new OpenZFS implementations for Windows and macOS each have their own Solaris Porting Layer, too.
If what you want is just snapshotting and you want something that's in the mainline kernel, I guess there's BTRFS. Bcachefs seems to be coming along nicely, but who knows when it'll really be ready.
If what you want is just snapshotting and you want something that's in the mainline kernel, I guess there's BTRFS. Bcachefs seems to be coming along nicely, but who knows when it'll really be ready.
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1: https://papers.freebsd.org/2019/BSDCan/jude-The_Future_of_Op...