Fair enough, though you can’t really understand how BTRFS works without reading the GPLed Linux source while ZFS has some separate disk format documentation. Don’t know that anyone would sue you though.

Its not unreasonable to look at the source code to understand the disk format to then create an independent driver. So long as you are not directly copying code (or in this case, paraphrasing C to Rust.)

More importantly though, Linux or the Linux Foundation are unlikely to file a lawsuit without clear evidence of infringement, whereas Oracle by their nature will have filed lawsuits and a dozen motions if they catch even a whiff of possible infringement.

I wouldn't touch Oracle IP with a 50' fibreglass pole while wearing rubber boots.