The System Call Interface
Each process thread consists of a bound user/kernel thread pair (unless a user-space scheduler is used). This thread is executing instructions from either the process's user memory space or from the privileged memory space of a legitimate kernel system call at any one instance of time. In addition to the many process-based threads, at times the system is required to halt the execution of the currently scheduled thread and switch to a specific kernel-only thread for the performance of interrupt handling, scheduling, or a host of other operating system-related tasks.
The transition between these various modes of operation is the study of the system call interface and the interrupt system (see Figure 4-4). We discussed ...
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