Editing XNU (section)

===IOKit===
IOKit is the [[device driver]] framework, written in a subset of [[C++]] based on [[Embedded C++]].<ref>{{Cite web |url=http://osxbook.com/book/bonus/ancient/whatismacosx/arch_xnu.html |work=What is Mac OS X? |title=XNU: The Kernel |at=I/O Kit |quote=I/O Kit uses a restricted subset of C++ |author=Amit Singh |access-date=September 9, 2011 |archive-date=April 19, 2019 |archive-url=https://web.archive.org/web/20190419152142/http://osxbook.com/book/bonus/ancient/whatismacosx/arch_xnu.html |url-status=dead}}</ref> Using its [[object-oriented programming|object-oriented]] design, features common to any class of driver are provided within the framework, helping device drivers be written in less time and code. IOKit is multi-threaded, [[symmetric multiprocessing]] (SMP)-safe, and allows for hot-pluggable devices and automatic, dynamic device configuration.

Many drivers can be written to run in [[User space and kernel space|user mode]], which further enhances the stability of the system. If a driver running in user mode crashes, it will not crash the kernel. However, if a driver running in kernel mode crashes it will crash the kernel. Examples of drivers running in kernel mode include disk adapter and network adapter drivers, graphics drivers, drivers for Universal Serial Bus ([[USB]]) and [[FireWire]] [[Host controller interface (USB, Firewire)|host controllers]], and drivers for [[virtual machine]] software such as [[VirtualBox]], [[Parallels Desktop for Mac]], and [[VMware Fusion]]. In [[macOS Catalina]] and later releases, DriverKit allows some of those types of drivers to run in user mode.<ref>{{cite web|url=https://developer.apple.com/documentation/driverkit|title=DriverKit|website=Apple Developer}}</ref>