Operating System Structure#

Operating-System Services#

• User interface (UI): 給 User 下指令
  • Graphic user interface (GUI): 圖形化介面
• Program Execution:
  • Process 的 normal/abnormal interrupt
  • load program to memory
• I/O Operation
• File-System Manipulation
  • 包含 access management
• Communication
  • Maybe in share memory or bus
• Error Detection
• Resource Allocation
• Accounting (Logging)
  • 紀錄
• Protection and Security

User and Operating-System Interface#

• Command interpreters:
  • Shell 就是一種直譯器
  • Shell script 就是 command 的組合
• GUI
• Application Programming Interface (API)

System call#

• System call 也是一種 OS 提供的 Interface

Application Programming Interface (API)#

• 為了 portability，通常不直接 call system call，不然有可能出問題
  • Windows 裡用 CreateProcess() 創建，但其實他不是 System call 他會呼叫 NTCreateProcess

System-Call Interface#

• 用查表的方法最快，在 kernel 裡有個 table 去到指定 system call 位置，執行後，透過 interface 回傳
• Caller 不需要知道底層在做啥，不然效率太低了

Parameter Passing#

1. In register
2. In memory
   • address 當作

• Linux 用 1&2 combine (5 個以上用 approach 2)

3. In stack (資料量更大)

Type of System call#

1. Process Control
   • create process, terminate process
   • load, execute
   • get process attributes, set process attributes
   • wait event, signal event
   • allocate and free memory
   • end, abort
   • Debugger
   • Lock shared data
2. File management
   • create file, delete file
   • open, close
   • read, write, reposition
   • get file attributes, set file attributes
3. Device management
   • request device, release device
   • read, write, reposition
   • get device attributes, set device attributes
   • logically attach or detach devices
4. 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
5. Communications
   • create, delete communication connection
   • send, receive messages
   • transfer status information
   • attach or detach remote devices
   • Message-passing model and shared-memory model
6. Protection
   • get file permissions, set file permissions

Linkers & Loaders#

• Compiler 會把 program compile 成一個 Relocatable Object File
• Linker 會把 Object File 跟其他 Obj file 去 combine 成一個 executable file
• 最後真正執行的是 Loader 會把其他 DLL (Dynamic Link Library) 合併進來，load 到 memory 裡

DLL 的出現是希望 executable file 不要太大

• 中間會有 Relocation 這個重新分配記憶體位置的步驟

Operating-System Structure#

Monolithic Structure#

• Simple (單純) but not necessarily easy

  • 所有功能都是同地位，System call 跟 hardware 都包在一起
  • Traditional Unix System Structure
  
  

  Monolithic Structure 2

  • Linux Structure
  

Layered Approach#

• Network
• 只能碰到自己的上層跟下層，越界碰不到

Microkernels#

• Kernel 要極小，除了最基本的其他都給 User mode 實現
• 安全，extendable 但 not efficient
• 用 Message Passing 傳資料

Modules#

• Loadable kernel modules (LKMs)
  • Kernel 有基本功能
  • Dynamic 的去加入一些東西
• 現在的系統通常都有實現這件事

Hybrid System#