The Second Extended File System Internal Layout Dave Poirier [email protected] The Second Extended File SystemInternal Layout by Dave Poirier Copyright © 2001-2011 Dave Poirier Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license can be acquired electronically from http://www.fsf.org/licenses/fdl.html or by writing to 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Table of Contents About this book....................................................................................................................................... vii 1. Historical Background..........................................................................................................................1 2. Definitions...............................................................................................................................................2 2.1. Blocks..........................................................................................................................................2 2.2. Block Groups..............................................................................................................................3 2.3. Directories...................................................................................................................................3 2.4. Inodes..........................................................................................................................................4 2.5. Superblocks.................................................................................................................................4 2.6. Symbolic Links...........................................................................................................................5 3. Disk Organization..................................................................................................................................7 3.1. Superblock..................................................................................................................................8 3.1.1. s_inodes_count.............................................................................................................10 3.1.2. s_blocks_count.............................................................................................................10 3.1.3. s_r_blocks_count..........................................................................................................10 3.1.4. s_free_blocks_count.....................................................................................................11 3.1.5. s_free_inodes_count.....................................................................................................11 3.1.6. s_first_data_block.........................................................................................................11 3.1.7. s_log_block_size..........................................................................................................11 3.1.8. s_log_frag_size.............................................................................................................11 3.1.9. s_blocks_per_group......................................................................................................12 3.1.10. s_frags_per_group......................................................................................................12 3.1.11. s_inodes_per_group....................................................................................................12 3.1.12. s_mtime......................................................................................................................12 3.1.13. s_wtime.......................................................................................................................12 3.1.14. s_mnt_count...............................................................................................................13 3.1.15. s_max_mnt_count.......................................................................................................13 3.1.16. s_magic.......................................................................................................................13 3.1.17. s_state.........................................................................................................................13 3.1.18. s_errors.......................................................................................................................13 3.1.19. s_minor_rev_level......................................................................................................14 3.1.20. s_lastcheck..................................................................................................................14 3.1.21. s_checkinterval...........................................................................................................14 3.1.22. s_creator_os................................................................................................................14 3.1.23. s_rev_level..................................................................................................................14 3.1.24. s_def_resuid................................................................................................................15 3.1.25. s_def_resgid................................................................................................................15 3.1.26. s_first_ino...................................................................................................................15 3.1.27. s_inode_size...............................................................................................................15 3.1.28. s_block_group_nr.......................................................................................................15 3.1.29. s_feature_compat........................................................................................................16 3.1.30. s_feature_incompat.....................................................................................................16 3.1.31. s_feature_ro_compat..................................................................................................17 3.1.32. s_uuid.........................................................................................................................17 3.1.33. s_volume_name..........................................................................................................17 3.1.34. s_last_mounted...........................................................................................................17 iii 3.1.35. s_algo_bitmap.............................................................................................................18 3.1.36. s_prealloc_blocks.......................................................................................................18 3.1.37. s_prealloc_dir_blocks.................................................................................................18 3.1.38. s_journal_uuid............................................................................................................18 3.1.39. s_journal_inum...........................................................................................................19 3.1.40. s_journal_dev..............................................................................................................19 3.1.41. s_last_orphan..............................................................................................................19 3.1.42. s_hash_seed................................................................................................................19 3.1.43. s_def_hash_version....................................................................................................19 3.1.44. s_default_mount_options...........................................................................................19 3.1.45. s_first_meta_bg...........................................................................................................19 3.2. Block Group Descriptor Table..................................................................................................19 3.2.1. bg_block_bitmap..........................................................................................................20 3.2.2. bg_inode_bitmap..........................................................................................................20 3.2.3. bg_inode_table.............................................................................................................21 3.2.4. bg_free_blocks_count...................................................................................................21 3.2.5. bg_free_inodes_count...................................................................................................21 3.2.6. bg_used_dirs_count......................................................................................................21 3.2.7. bg_pad..........................................................................................................................21 3.2.8. bg_reserved...................................................................................................................21 3.3. Block Bitmap............................................................................................................................21