Published at LXer:

In Linux you run processes in two different modes of execution. There is userspace (aka user mode) which you run your everyday applications, like Firefox, Pidgin, irssi. From the kernel’s point of view, this is unprivileged mode, meaning user space applications don’t have access to hardware, or bits of the system critical to its function. The next mode is kernelspace, in this mode a process runs in privileged mode, giving it access to hardware and low-level system processes. In this article I show how to write a kernel module.

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