Fuse-xfs Apr 2026

Want to understand delayed allocation? Step through xfs_iomap_write_delay() in userspace with printfs . Curious about AG btree splits? Corrupt an AG by writing random bytes and watch fuse-xfs segfault at the exact line of code where validation fails.

There’s a moment in every systems programmer’s life where they stare at a kernel panic, a corrupted superblock, or an unreachable inode, and think: “I wish I could just put a breakpoint inside the filesystem.” fuse-xfs

struct xfs_agf *agf = (struct xfs_agf *)(ag->map + XFS_AGF_OFFSET); if (be32_to_cpu(agf->agf_magicnum) != XFS_AGF_MAGIC) return -EINVAL; // or crash, which is more fun No buffer cache. No I/O scheduling. Just the filesystem’s raw data laid out in virtual memory. XFS’s extent B+tree is elegant: internal nodes point to other blocks, leaves point to extents. In kernel space, traversing it is cheap. In fuse-xfs , every bmap lookup might require reading several blocks—each of which is a pread() or a memory access, depending on your cache. Want to understand delayed allocation

Or, Why I Spent a Weekend Reimplementing a Journaling Filesystem as a Debugging Tool Corrupt an AG by writing random bytes and