Linux File System

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Linux File System

• Li-Shien Chen

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????
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????
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Inode
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Link

• ?????
• ?????????
• Hardlink
• ln /a/os1.txt /b/os2.txt

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Hard Link
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Hard Link ??

• ????????
• ???????
• ???????
• ???Inode number???

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Symbolic Link

• Ln s /a/os1.txt /b/os2.txt
• ?Hard Link???
• ????Inode??

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Symbolic Link
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??Unix??

• ???????????
• ???????????
• ????????????

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??Unix????
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???
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??????

• Kernel???????????
• ?????????
• ??? ?kernel??????????
• ??????

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???
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Linux File System

• ???????
• ?Ext2,FAT??
• Cache
• ???????????
• Virtual File System Switch(VFS)
• Kernel??????????

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Linux File System ??
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The Buffer Cache
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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

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The States of the Cache

• Share
• Shared buffers
• Unshared
• Buffers that were once shared but which are now
  not shared

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???????

• Disk and Patition Layout
• ?Linux?, ??????????partition????
• ?VFS?, ??????????superblock????

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VFS Superblock

• Super_block??
• 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

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VFS Superblock

• struct file_system_type type
• unsigned long s_flags
• unsigned long s_magic
• struct dentry s_root
• struct super_operations s_op

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?????

• ????? ????
• ? usr/src/linux/fs/file.c
• VFS?vfs inode(vnode)???

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VFS inode

• 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

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Registering the File Systems

• Build Linux kernel supported file systems
• Build file systems as module

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??????

• ?? mount ? mount_root()
• ??read_super()???superblock
• mount -t ext2 /dev/hda3 /mnt

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Example
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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

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A Mounted File System
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Unmount a File System

• Check whether someone is using the FS
• Check if the File System is dirty
• write back
• Return VFS superblock to kernels pool
• vfsmount is unlinked from vfsmntlist

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Reference

• The Linux Kernel
• Linux ?????
• http//www.linpus.com.tw
• http//cat.ice.ntnu.edu.tw