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Linux File System

Linux File System. Li-Shien Chen. 基本概念. 檔案屬性. Inode. Link. 何謂連結 ? 將檔案取另一個名字 Hardlink ln /a/os1.txt /b/os2.txt. Hard Link. Hard Link 缺點. 不許應用在目錄上 會造成循環連結 不能跨檔案系統 會使得 Inode number 不唯一. Symbolic Link. Ln –s /a/os1.txt /b/os2.txt 與 Hard Link 的不同

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Linux File System

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  1. Linux File System Li-Shien Chen

  2. 基本概念

  3. 檔案屬性

  4. Inode

  5. Link • 何謂連結? 將檔案取另一個名字 • Hardlink ln /a/os1.txt /b/os2.txt

  6. Hard Link

  7. Hard Link 缺點 • 不許應用在目錄上 會造成循環連結 • 不能跨檔案系統 會使得Inode number不唯一

  8. Symbolic Link • Ln –s /a/os1.txt /b/os2.txt • 與Hard Link的不同 有自己的Inode節點

  9. Symbolic Link

  10. 傳統Unix系統 • 支援某一種特定檔案系統 • 無法存取其他的檔案系統 • 如何同時支援多個檔案系統

  11. 傳統Unix系統缺點

  12. 方案一

  13. 方案一的問題 • Kernel與檔案系統相依程度太高 • 造成應用程式的負擔 • 方案二 :為kernel與檔案系統提供一個標 準的連結介面

  14. 方案二

  15. Linux File System • 真正的檔案系統 • 如Ext2,FAT…等等 • Cache • 加快讀取檔案系統的速度 • Virtual File System Switch(VFS) • Kernel與真正檔案系統的介面

  16. Linux File System 架構

  17. The Buffer Cache

  18. The States of the Cache • Locked • Buffers that are locked, waiting to be written • Dirty • Dirty buffers. These contain new, valid data, and will be written but so far have not been scheduled to write

  19. The States of the Cache • Share • Shared buffers • Unshared • Buffers that were once shared but which are now not shared

  20. 檔案系統的表示 • Disk and Patition Layout • 在Linux裡， 檔案放的位置是以一個partition為單位的 • 在VFS裡， 每一個檔案系統是由其superblock來表示的

  21. VFS Superblock • Super_block結構 struct list_heads s_list; kdev_t s_dev; unsigned long s_blocksize; unsigned char s_blocksize_bits; unsigned char s_rd_only; unsigned char s_dirt;

  22. VFS Superblock struct file_system_type *type; unsigned long s_flags; unsigned long s_magic; struct dentry *s_root; struct super_operations *s_op

  23. 檔案的表示 • 使用者觀點: 絕對路徑 如 usr/src/linux/fs/file.c • VFS:以vfs inode(vnode)來表示

  24. Device Inode Number Mode User id times block size inode operations a pointer to a block of routine addresses count lock dirty file system specific VFS inode

  25. Registering the File Systems • Build Linux kernel : supported file systems • Build file systems as module

  26. 掛上檔案系統 • 利用 mount 或 mount_root() • 利用read_super()來初始superblock • $mount -t ext2 /dev/hda3 /mnt

  27. Example

  28. Mounting a File System • $mount -t iso9600 -o ro /dev/cdrom /mnt/cdrom • Search for the file system types( iso9600) • Allocate a VFS superblock and pass it the mount information to the superblock read routine

  29. A Mounted File System

  30. Unmount a File System • Check whether someone is using the FS • Check if the File System is dirty • write back • Return VFS superblock to kernel’s pool • vfsmount is unlinked fromvfsmntlist

  31. Reference • The Linux Kernel • Linux 核心研究篇 • http://www.linpus.com.tw • http://cat.ice.ntnu.edu.tw

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