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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