# Operating System Structures

## Operating System Services


Providing functions that are helpful to users:

- **User Interface (UI)**
- GUI (Graphical User Interface)
- Touch-screen interface
- CLI (Command Line Interface)
- **Program execution**
- **I/O operations**
- **File system manipulation**
- **Communications**
- Shared memory
- Messaging passing
- **Error detection**

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- OS functions for ensuring the efficient operation of the system.
- System with multiple processes can gain efficiency by sharing the computer resources among the different processes.
- **Resource allocation**
- **Logging**
- **Protection and security**

## System Calls

### Application Programming Service

- API (Application Programming Interface)
- Application developers design program according to an API.
- Example of standard API
- System call interface

Three methods are used to pass parameters to the OS:

- Put in the ==registers==
- Put the ==block, table in memory==
- The address of the block is passed as a parameter in a register
- （這張圖看不懂正常）
- Put in a ==stack==
- Push
- Pop

### Types of System Calls

System calls can be grouped into six categories:

- **Process control**
- create process, terminate process
- load, execute
- get process attributes, set process attributes
- wait event, signal event
- allocate and free memory
- **File manipulation**
- create file, delete file
- open, close
- read, write, reposition
- get and set file attributes
- **Device manipulation**
- request device, release device
- read, write, reposition
- get device attributes, set device attributes
- logically attach or detach devices
- **Information maintenance**
- get time or date, set time or date
- get system data, set system data
- get process, file, or device attributes
- set process, file, or device attributes
- **Communications**
- create, delete communication connection
- send, receive messages
- transfer status information
- attach and detach remote devices
- Message-passing model
- Shared memory model
- **Protection**
- Get file permissions
- Set file permissions

## System Services (System Utilities)

- Provide a convenient environment for program development and execution.
- Categories
- File management
- Status information
- File modification
- Programming language support
- Program loading execution
- Communications
- Background services

## Linkers and Loaders


## Why Applications are Operating System Specific

An application can run on multiple OS in one of three ways:

- The application can be written in an interpreted language that has an **interpreter** available for multiple OSs.
- The application can be written in a language that includes a **virtual machine** containing the running application.
- The application developer can use a standard language or API in which the **compiler** generates binaries in a machine-specific and OS-specific language.

## Operating System Design and Implementation

### Design Goals

- User goals
- convenient to use, easy to learn, reliable, safe, and fast
- System goals
- easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient

### Mechanisms and Policies

（考點？）

- Mechanisms 機制
- determine ==how== to do something
- Policies 政策
- determine ==what== will be done

### Implementation

- In assembly language
- In C
- In C++

## Operating System Structure

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### Monolithic Structure

Place all of the functionality of the kernel into a single, static binary file that runs in a singe address space.

- UNIX
- Linux

### Layer Approach


- The OS is broken into a number of layers (Fig 2.14)
- The bottom layer (layer 0) is the hardware
- The highest layer (layer N) is the user interface
- The layers are selected such that each uses functions (operations) and services of only lower-level layers.
- Simplifying debugging and system verification

### Microkernal


(Fig 2.15)

Removing all **nonessential** components from the kernel and implementing them as system and user-level programs.

- Benefits
- Easier to extend
- Easier to port
- More secure
- More reliable
- Disadvantage
- Performance can suffer from due to increased system-function overhead

### Modules

Loadable kernel modules:

- The kernel has a set of core components and links in additional services via modules, either at boot time or during run time.
- The kernel provides core services while other services are implemented ==dynamically==.
- Linking services dynamically.

### Hybrid Systems

- Combining different structures, resulting in hybrid systems.
- Address performance, security, usability issues.

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## Building and Booting an Operating System

### Operating System Generation

- System generation
- The system must then be configured or generated for each specific computer site

### System Boot

- Booting
- The procedure of starting a computer by loading a kernel.
- The boot process proceeds as follows
1. A small piece of code known as the **bootstrap program** or **bootstrap loader** locates the kernel.
2. The kernel is loaded into memory and started.
3. The kernel initializes hardware.
4. The root file system is mounted.

## Operating System Debugging

- Debugging
- Finding and fixing errors in a system, both in hardware and software.
- Performance tuning
- Improving performance by removing processing bottlenecks.

### Failure Analysis

- Log file
- Core dump
- Crash dump

### Performance Monitoring and Tuning


### Tracing

### BCC


[BPF Compiler Collection](https://github.com/iovisor/bcc)