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Comment by macshome | Hacker News Reader

Apple started replacing their own file system (and networking) kexts with user-mode file systems in macOS 13. Right now its locked up behind some private entitlements though. Hopefully they open it up more in the future.

For a quick overview check out a blog post on threedots. https://threedots.ovh/blog/2022/06/quick-look-at-user-mode-f...

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It’s certainly been interesting watching the multi-decade arc play out. With Mach as the origins, everything other than tasks (processes) schedule and virtual mem was out of kernel and done over Mach port comms. Then xnu via next step and later OS X linked much more in kernel and exposed specific data types using com+ in iokit. And now more and more is moving back out of the kernel.

io_urging networking on Linux is another similar move out to use space

Its my favorite part of watching the mac evolve. The man hours that has been used in the development is staggering.

The linked msdos source code on GitHub has since been rewritten by Apple /again/ [1], so the article is a bit out of date. This happened 3 months ago, and it now plugs into a private framework named FSKit.

I did not immediately see any private entitlements that restrict access to this API, nor is msdos.fs signed with special entitlements on my machine. Chances are this API works for any filesystem by dropping an appex into /Library/Filesystems. Looking forward to this being documented and made public eventually.

[1] https://github.com/apple-oss-distributions/msdosfs/blob/423d...

Thanks. I was aware of FAT being the first filesystem in userspace (maybe for iOS devices to mount SD cards?) but did not know it was open source or that FSKit existed. Maybe an enterprising hacker could dump the Obj-C header from that framework and start writing a FUSE translation layer.

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