So when I decided to write fuse-xfs —a userspace implementation of the —I wasn’t trying to build a production storage engine. I was trying to answer a single question: Can we take the soul of XFS (its allocation groups, B+tree extents, and delayed allocation) and lift it into userspace without losing its identity? Here’s what I learned. The Heresy: Userspace XFS XFS, designed by SGI in the ’90s, is a kernel beast . It assumes it owns the hardware. It assumes it can reorder writes, bypass the page cache when needed, and manipulate memory directly via kmem_cache . Porting that to userspace is not just difficult—it’s borderline heretical.
This is where the kernel-to-userspace shift gets interesting. In the kernel, XFS uses xfs_buf_t with b_ops for verification. In fuse-xfs , we just cast: fuse-xfs
And when someone asks, “Why would you run a filesystem in userspace?” — you’ll know the answer. So when I decided to write fuse-xfs —a
Or, Why I Spent a Weekend Reimplementing a Journaling Filesystem as a Debugging Tool The Heresy: Userspace XFS XFS, designed by SGI
But fuse-xfs isn’t a port. It’s a reconstruction .