System call Preliminary

System call System Programming
High efficiency, typically used in server applications.

System call: A set of functions provided by the operating system. Kernel functions, manipulating external resources.
System call is the interface provided by the kernel to the application, only the system provides the function, the user can call it, implement the corresponding function, do not provide the function, the operating system does not provide this function.

Operating system features: 1) management hardware, 2) abstract hardware.

There are three main contents in the System call section:
1) File: File I/O, file system.
2) Process thread: process, Thread, IPC
3) Protocol: Tcp,udp,socket (local)

Under Linux, the program has two privileged levels: User-state and kernel-state.
Power-level switching: The conversion of the kernel state and the user state, which is quite time consuming.

Privileged Pole reference: http://my.oschina.net/liubin/blog/27795

System call Preliminary