Tagged: #xnu

clonefile, fclonefileat, fs_snapshot — three syscalls that let you copy 50 GB in 50 milliseconds. Here's what happens under each one, and what doesn't get copied.

What changed in XNU when Apple shipped its own ARM silicon — P/E cores, APRR page-permission switching, the AMX matrix coprocessor, and Rosetta 2.

Same IOKit object model, userland process. Why kexts are dying, what DriverKit gives you, and how a USB driver actually crosses the boundary.

POSIX says signals are per-process. Mach says everything is a thread. Here's how XNU bridges the two — pending masks, delivery threads, the AST mechanism, and exception ports.

Real-time, fixed-priority, timeshare, idle — four scheduling classes, 128 priorities, and a QoS layer on top. Here's how XNU picks a thread to put on a core.

Apple File System, the format under every modern Mac: how it lays out blocks, how it gets snapshots almost for free, and why your /System is read-only at the cryptographic level.

Embedded C++, an object tree, and matching dictionaries — IOKit is how every driver on macOS gets loaded, paired with hardware, and called.

Tasks, ports, messages, and rights — the IPC primitive that quietly carries every IPC on your Mac, from XPC to drag-and-drop.

Processes, file descriptors, signals, sockets — the FreeBSD-derived layer that sits on top of Mach and makes macOS pass POSIX.

Every macOS process gets a private address space it can't possibly afford. Here's how XNU gives it one anyway — pmap, vm_map, the compressor, and jetsam.