Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Linux File System


Published on

Published in: Technology
  • ⇒⇒⇒ ⇐⇐⇐ has really great writers to help you get the grades you need, they are fast and do great research. Support will always contact you if there is any confusion with the requirements of your paper so they can make sure you are getting exactly what you need.
    Are you sure you want to  Yes  No
    Your message goes here
  • There is a useful site for you that will help you to write a perfect and valuable essay and so on. Check out, please ⇒ ⇐
    Are you sure you want to  Yes  No
    Your message goes here
  • I’ve personally never heard of companies who can produce a paper for you until word got around among my college groupmates. My professor asked me to write a research paper based on a field I have no idea about. My research skills are also very poor. So, I thought I’d give it a try. I chose a writer who matched my writing style and fulfilled every requirement I proposed. I turned my paper in and I actually got a good grade. I highly recommend ⇒ ⇐
    Are you sure you want to  Yes  No
    Your message goes here
  • Hello! I do no use writing service very often, only when I really have problems. But this one, I like best of all. The team of writers operates very quickly. It's called ⇒ ⇐ Hope this helps!
    Are you sure you want to  Yes  No
    Your message goes here
  • Dating direct: ❶❶❶ ❶❶❶
    Are you sure you want to  Yes  No
    Your message goes here

Linux File System

  1. 1. Linux File System© 2010 Anil Kumar Pugalia <> All Rights Reserved.
  2. 2. What to Expect?Ws of a File SystemThree Levels of File System © 2010 Anil Kumar Pugalia <> 2 All Rights Reserved.
  3. 3. What is a File System?Mechanism of Organizing our Data Labelling by Names, Easy Access, ...Algorithm to Achieve the DesiredOrganization Ability to Store, Retrieve, Search, Sort, ...Data Structures to Achieve the DesiredPerformance © 2010 Anil Kumar Pugalia <> 3 All Rights Reserved.
  4. 4. Why we need a File System?Preserve Data for Later Access Update DiscardTag Data for Categorizing Easy & Fast LookupFast & Reliable Data Management by Optimized Operations © 2010 Anil Kumar Pugalia <> 4 All Rights Reserved.
  5. 5. File System DecodedThree things at three levels Hardware Space – The Physical Organization of Data on the Storage Devices Kernel Space – Drivers to decode & access the data from the Physical Organization User Space – All what you see from / - The User ViewWhich ever it be, it basically does Organize our data For easy access by tagging For fast maintenance by optimizing © 2010 Anil Kumar Pugalia <> 5 All Rights Reserved.
  6. 6. Hardware Space File System © 2010 Anil Kumar Pugalia <> 6 All Rights Reserved.
  7. 7. The Hard Disk Tracks SectorsDisk orPlatter © 2010 Anil Kumar Pugalia <> 7 All Rights Reserved.
  8. 8. The Hard Disk Spindle Heads . .Cylinder . . . . © 2010 Anil Kumar Pugalia <> 8 All Rights Reserved.
  9. 9. Understanding a Hard DiskExample (Hard Disk) Heads (or Platters): 0 – 9 Tracks (or Cylinders): 0 – 24 Sectors: 1 – 64Size of the Hard Disk 10 x 25 x 64 x 512 bytes = 8000KiBDevice independent numbering (h, t, s) → 64 * (10 * t + h) + s → (1 - 16000) © 2010 Anil Kumar Pugalia <> 9 All Rights Reserved.
  10. 10. Partitioning a Hard DiskFirst Sector – Master Boot Record (MBR) Contains Boot Info Contains Physical Partition TableMaximum Physical Partitions: 4 At max 1 as Extended Partition Rest as Primary PartitionExtended could be further partitioned into Logical PartitionsIn each partition First Sector – Boot Record (BR) Remaining for File System / Format Extended Partition BR contains the Logical Partition Table © 2010 Anil Kumar Pugalia <> 10 All Rights Reserved.
  11. 11. Placement of a Hardware FSEach Partition contains a File System Raw (no FS) OrganizedOrganized one is initialized by the correspondingFormating“Partition Type is to OS” W95*, DOS*, BSD*, Solaris*, Linux, ...“Format Type is to File System” ext2, ext3, vfat, ntfs, jffs2, …Particular Partition Types support only Particular FileSystem Types © 2010 Anil Kumar Pugalia <> 11 All Rights Reserved.
  12. 12. Design a FSLets Take 1 PartitionWith 16 blocks of 2 sectors eachSize = 16 x 2 x 512 bytes = 16KBGiven 3 data pieces Source Code – 2.5KB Image – 8KB Document – 2KBPlace optimally for further operations © 2010 Anil Kumar Pugalia <> 12 All Rights Reserved.
  13. 13. Kernel Space File System© 2010 Anil Kumar Pugalia <> 13 All Rights Reserved.
  14. 14. Kernel Space File SystemHas 2 Roles to Play Decode the Hardware FS Layout to access data (by implementing your logic in s/w) Interface that with the User Space FS to give you a unified view, as you all see at /First part: ext2, ext3, vfat, ntfs, jffs2, … Also called the File System modulesSecond part: VFS Kernel provides VFS to achieve the virtual user view So, FS module should actually interact with VFS © 2010 Anil Kumar Pugalia <> 14 All Rights Reserved.
  15. 15. Linux specific File SystemsInitial Linux: Minix FSAs Linux matured: Extended (ext) FS1994: Second Extended (ext2) FSLatest: Third Extended (ext3) FSFeatures Introduced: Access Control Lists (ACL) Block Fragmentation Logical Deletion Journaling © 2010 Anil Kumar Pugalia <> 15 All Rights Reserved.
  16. 16. Linux FS Data StructuresSuper block – Stores filesystem meta dataInode – Stores file meta dataDirectory Entry – Stores file name & inodenumberInode & Data block Bitmap – Bitmap fortracking usage status of the variousblocksGroup Entry – Stores information ofgroups of Data Storage © 2010 Anil Kumar Pugalia <> 16 All Rights Reserved.
  17. 17. Linux FS TransitionsChoosing Optimal Block Size (from 1KiB to4KiB), depending on the expected average filelengthChoosing Number of InodesPartition Groups: Each group includes DataBlocks and Inodes stored in adjacent tracksPreallocating Disk Data Blocks to Regular FilesFast Symbolic Links © 2010 Anil Kumar Pugalia <> 17 All Rights Reserved.
  18. 18. File System related CommandsFile and Inode information – statHardlinks and Softlinks – ln & ln -sMounting filesystem – mount & umountCreating special files – mknod, mkfifoPermission related – chmodOwnership related – chown, chgrpTimestamp related – touch © 2010 Anil Kumar Pugalia <> 18 All Rights Reserved.
  19. 19. Case Study: ext2/ext3© 2010 Anil Kumar Pugalia <> 19 All Rights Reserved.
  20. 20. ext2/ext3: Disk Data Structure Boot Block group 0 ... Block group n blockSuper Group Data block Inode Inode Data blocksblock Descriptors Bitmap Bitmap Table1 block n blocks 1 block 1 block n blocks n blocks Superblock and Group Descriptors are duplicated in each Block Group Superblock and Group Descriptors in Block Group 0 are used by the kernel © 2010 Anil Kumar Pugalia <> 20 All Rights Reserved.
  21. 21. ext2/ext3: Superblockunsigned long s_frag_size; /* Size of a fragment in bytes */unsigned long s_frags_per_block; /* Number of fragments per block */unsigned long s_inodes_per_block; /* Number of inodes per block */unsigned long s_frags_per_group; /* Number of fragments in a group */unsigned long s_blocks_per_group; /* Number of blocks in a group */unsigned long s_inodes_per_group; /* Number of inodes in a group */unsigned long s_itb_per_group; /* Number of inode table blocks per group */unsigned long s_gdb_count; /* Number of group descriptor blocks */unsigned long s_desc_per_block; /* Number of group descriptors per block */unsigned long s_groups_count; /* Number of groups in the fs */... © 2010 Anil Kumar Pugalia <> 21 All Rights Reserved.
  22. 22. ext2/ext3: Group Descriptor__le32 bg_block_bitmap; /* Blocks bitmap block number */__le32 bg_inode_bitmap; /* Inodes bitmap block number */__le32 bg_inode_table; /* Inodes table first block number */__le16 bg_free_blocks_count; /* Free blocks in the group */__le16 bg_free_inodes_count; /* Free inodes in the group */__le16 bg_used_dirs_count; /* Directories in the group */__le16 bg_pad; /* Alignment to word */__le32 bg_reserved[3]; /* Nulls to pad out 24 bytes */ © 2010 Anil Kumar Pugalia <> 22 All Rights Reserved.
  23. 23. ext2/ext3: Inode EntryInode Table consists of Inode Entries. An Inode Entry is as follows __le16 i_mode; /* File type & access rights */ __le16 i_uid; /* Low 16 bits of owner uid */ __le32 i_size; /* File size in bytes */ __le32 i_atime; /* Last file access time */ __le32 i_ctime; /* File creation time */ __le32 i_mtime; /* Last file contents modification time */ __le32 i_dtime; /* File deletion time */ __le16 i_gid; /* Low 16 bits of group id */ __le16 i_links_count; /* Hard links counter */ __le32 i_blocks; /* Number of data blocks of the file */ __le32 i_flags; /* File flags */ union osd1; /* OS specific information */ __le32 i_block[12 + 3]; /* Pointers to data blocks */ ... © 2010 Anil Kumar Pugalia <> 23 All Rights Reserved.
  24. 24. ext2/ext3: File TypesFile Types supportedFile Type Value Description0 Unknown1 Regular2 Directory3 Character Device4 Block Device5 Named Pipe6 Socket7 Symbolic Link © 2010 Anil Kumar Pugalia <> 24 All Rights Reserved.
  25. 25. ext2/ext3: Directory EntryDirectory is a File, with Data Blockscontaining Directory EntriesA Directory Entry is as follows __le32 inode; /* Inode number */ __le16 rec_len; /* Directory entry length */ __u8 name_len; /* Name length */ __u8 file_type; /* File type */ char name[255]; /* File name */ © 2010 Anil Kumar Pugalia <> 25 All Rights Reserved.
  26. 26. Virtual File System© 2010 Anil Kumar Pugalia <> 26 All Rights Reserved.
  27. 27. VFS SpecificsInherited from the Linux specific FSPromoted to a super set of various FSProvides a unified view to the UserDefault values for various attributes owner, group, permissions, …File Types Same seven types as in ext2/ext3 © 2010 Anil Kumar Pugalia <> 27 All Rights Reserved.
  28. 28. Virtual File System Interactions User Space File System View @ / VFS .... ext2 .... vfat .... Partition 0 Partition 1 ... Partition N ... © 2010 Anil Kumar Pugalia <> 28 All Rights Reserved.
  29. 29. Virtual File System Internals d r Super Block Directory Entry Table Inode Table> FS Meta Data> Root Inode Number > File Name > Inode Number > File Meta Data > File Data Block Nos Data Block © 2010 Anil Kumar Pugalia <> 29 All Rights Reserved.
  30. 30. Recall: User Space File System © 2010 Anil Kumar Pugalia <> 30 All Rights Reserved.
  31. 31. / & the System Directories/bin, /sbin - system binaries/applications/var - logs, mails/proc, /sys - “virtual” windows into the kernel/etc - configuration files/lib - shared system libraries/dev - device files/boot - Linux kernel and boot related binary files/opt - for third-party packages/root, /home - home directory for super user & other users/usr - user space related files and dirs (binaries, libraries, ...)/tmp - scratch pad/mnt - mount points © 2010 Anil Kumar Pugalia <> 31 All Rights Reserved.
  32. 32. What all have we learnt?Ws of a File SystemThree Levels of File System Hardware Space Kernel Space User Space © 2010 Anil Kumar Pugalia <> 32 All Rights Reserved.
  33. 33. Any Queries?© 2010 Anil Kumar Pugalia <> 33 All Rights Reserved.