Investigate Apple's FSKit as a FUSE replacement

[mmmarcos]

FSKit is a new framework introduced by Apple for implementing user-space file systems on macOS. It intends to replace the old approach based on FUSE (Filesystem in Userspace). FSKit is available since macOS 14 (Sonoma) as a private framework, but it has been officially integrated and documented since macOS 15.4.

macFUSE (the driver required to support Parsec mountpoints on macOS) integrates FSKit backend since v5.0 allowing file systems to run entirely in user space on macOS 26. This eliminates the need to reboot into recovery mode to activate kernel extensions. To mount a file system with the FSKit backend, use the -o backend=fskit option.

This is not currently supported by the fuser crate, see cberner/fuser#306.

Some things to consider for a POC (non-exhaustive list):

• Make sure there is no cache or that it can be disabled: cache is not wanted in our case since the data should not remain on disk after Parsec logout/quit.
• We might want to check fskit-rs
• Assess risk of vendor lock-in

[mmmarcos]

According to this article (in French):

FUSE-T, another implementation of FUSE on macOS (which does not require a kernel extension, unlike macFUSE), will steer clear of FSKit in the short term. After a discussion with an Apple engineer, its developer believes that the new framework is not relevant at this time. In this exchange, the Cupertino employee pointed out that FSKit was not designed for network volumes, while stating that he was well aware of this request.