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New system calls are added pretty rarely. Most new kernel functionality can be reached through a few general mechanisms: File descriptors are a very general feature for resource management. Custom actions on file descriptors happen through ioctl. Interactions are also possible through the proc filesystem and its variant sysfs for hardware- and driver-...


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Forget about real mode, that's just a detail of the x86 architecture and it's just there for compatibility with 1980's processors. The processor indeed has a flag that indicates the current privilege level. The details of that flag vary between processor types but to keep things simple just think of it as two settings: user and kernel. There are processor ...



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