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Subsystem · The driver framework

IOKit

A C++ object model that turns hardware into a tree of nodes, matched at boot and unloaded on demand.

apple-oss-distributions/xnuiokit/Kernel/IOService.cppStart reading the kernel source here.View on GitHub(line —)
IORegistry treeThe IORegistry is a parent/child tree of IOService instances rooted at the platform expert. Userspace attaches via IOUserClient.IORegistryEntryrootIOPlatformExperthardware bring-upIOPCIBridgeiokit / pciIOACPIPlatformExpertiokit / acpiAppleARMPMUiokit / armIOPlatformBatteryManagementiokit / batteryIOPCIDevicevendor 0x14e4IOPCIDevicevendor 0x8086AppleBCM43xxWi-Fi drivermatchesuserspace appIOServiceOpenIOConnectCallMethodIOUserClientiokit/Kernelmach_msgEvery node here is reachable from ioreg -l. Live tree, queried by anything (debugger, power manager, fan controller).
IOKit: structure at a glance.

Articles in this series

IOKit and the driver model: how a Mac talks to its hardware
Embedded C++, an object tree, and matching dictionaries — IOKit is how every driver on macOS gets loaded, paired with hardware, and called.
iokitdriverskernelxnu
DriverKit: how Apple is moving every driver out of the kernel
Same IOKit object model, userland process. Why kexts are dying, what DriverKit gives you, and how a USB driver actually crosses the boundary.
iokitdriverkitdriverskernel
Power management on macOS: IOPM, idle states, and wake from sleep
How XNU tells every driver to drop power when idle and bring it back when needed — the IORegistry-walked power graph, IOPMrootDomain, and the sleep/wake choreography.
iokitpower-managementiopmkernel
Interrupt handling in IOKit: from device IRQ to driver callback
The full path of an interrupt from the device asserting a line, through the AIC, through XNU's exception handler, to the driver's IOInterruptDispatchSource callback running on a workloop.
iokitinterruptsworkloopkernel
How a USB device gets driven on macOS
From plug-in to working app — IOUSBHost enumeration, IOKit matching, the DriverKit dext load, the user-space SDK. A complete trace of one device's journey through the stack.
iokitusbdriverkitkernel
IOSurface in depth: zero-copy between every coprocessor
The IOKit object that lets CPU, GPU, ANE, ISP, and media engines share the same physical pages. The unifying primitive behind unified memory's performance story.
iokitiosurfacegpumetal