Linux Kernel Structure

Linux kernel structure

• Operating System is a resource manager

• Resource

  Physical resource	Abstract resource
  CPU	Task
  Memory	Segment, Page
  Disk	File
  Network	Communication protocol, Packet

  • Abstract resource only
    • Security
    • Access control

• Linux kernel’s conceptual structure

  

  Linux kernel offers services in the user space with system calls through the system call interfaces.

  • Linux Kernel (Conceptual Structure)
    • Task Manager
      • Task creation
      • Task execution
      • State transition
      • Scheduling
      • Signal Handling
      • Inter Process Communication
    • Memory Manager
      • Physical memory management
      • Virtual memory management
      • Segmentation
      • Paging
      • Page fault handling
    • File System
      • File creation
      • Access control
      • inode management
      • Directory management
      • Super block management
    • Network Manager
      • Socket interface
      • TCP/IP communication protocol
    • Device Drive Manager
      • Manage device drivers for Disk, Terminal, CD, Network card, etc.
• Linux kernel source level structure

  • Source tree under “/usr/src/kernels/” (branch “linux-4.19.y”)

    

    • /kernel directory
      • Implementation of the Task manager
      • HW dependent task managing logics are in /arch/$(ARCH)/kernel.
        • $(ARCH) is i386, arm, etc.
    • /arch directory
      • Acronym of “architecture”
      • /arch/$(ARCH)/kernel
        • $(ARCH) is i386(Intel), arm (Advanced RISC Machine), 68 series(Motorolla), Sparc(SUN), PPC(Power PC, IBM) etc.
          • /arch/x86

          Source Directory	Description
          /arch/x86/boot	bootstrap code for system booting
          /arch/x86/kernel	HW dependent task manage code like context switch
          /arch/x86/mm	HW dependent memory manage code like page fault handling
          /arch/x86/lib	library function code used by the kernel
          /arch/x86/math-emu	FPU(Floating Point Unit) emulator

    • /fs directory
      • System call implementation like open(), read(), write()
      • At least 60 different file systems are available for Linux
        • Representative file systems are ext2, ext3, ext4, nfs, fat, proc, sysfs, devfs, isofs, ntfs, reiserfs, f2fs, xfs, etc.
      • Virtual File System for offering consistent interface for user
    • /mm directory
      • Implementation of the Memory manager
      • Physical memory management
      • Virtual memory management
      • Memory object allocated for each task management
    • /driver directory
      • Implementation of the Device manager
      • Management and virtualization of Disk, Terminal, Network card, etc.
      • 3 different device drivers
        • Block Device Driver accessed by the file system
        • Character Device Driver accessed by user application program through its device file
        • Network Device Driver accessed by TCP/IP
      • Others: 3 categories are not enough because of many kinds of different devices like USB, LCD, DSP, Sound, etc.
    • /net directory
      • Decent portion of the whole linux kernel source amount
      • Many different network protocols are available like TCP/IP, UNIX domain communication protocol, 802.11, IPX, RPC, AppleTalk, bluetooth, etc.
      • Implementation of Abstract layer of many different communication protocol
      • Implementation of Socket offering user interface
    • /ipc directory
      • Implementation of Inter-Process Communication supported by linux kernel
      • Representative IPCs are PIPE(/fs), Signal(/kernel), SYS V IPC, Socket(/net), etc.
      • Implementation of message passing, shared memory, semaphore, etc.
    • /init directory
      • Implementation of main start function to initialize the kernel
      • /arch/$(ARCH)/kernel:
        • HW dependent initialization at “head.S” and “mics.c”
        • Global kernel initialization at start_kernel()
    • /include directory
      • Linux kernel headers at /include/linux
      • HW dependent headers at /include/asm-$(ARCH)
    • other directory
      • /Documentation directory for descriptions
      • /lib directory for implementation of kernel library functions
      • /scripts directory for scripts used when configure and compile the kernel

    Physical resource	Abstract resource	Conceptual Manager	Source directory
    CPU	Task	Task Manager	/kernel
    Memory	Segment, Page	Memory Manager	/mm
    Disk	File	File System	/fs
    Network	Communication protocol, Packet	Network Manager	/ipc
    Devices	Device drivers for each devices	Device Manager	/driver

Linux kernel compile

• For new version of linux kernel, just compile and reboot the new kernel.

  	hello.out	kernel
  executable	hello.out	bzImage or zImage
  stored at	file system	memory
  access level	user level	kernel level
  compile	gcc	gcc with make file

• 3 steps for making linux kernel

  1. Kernel configuration
  2. Kernel compile
  3. Kernel installation