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Linux Filesystems

Linux Filesystems. 9662815 林承諺 9662822 關啟邦. Linux Filesystems: The Virtual Filesystem. Outline. VFS Filesystem Types Common File Model Structure of VFS Mount Path lookup open read. VFS- Virtual Files System. To Support various native filesystems

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Linux Filesystems

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  1. Linux Filesystems 9662815 林承諺 9662822 關啟邦

  2. Linux Filesystems: The Virtual Filesystem

  3. Outline • VFS • Filesystem Types • Common File Model • Structure of VFS • Mount • Path lookup • open • read

  4. VFS- Virtual Files System • To Support various native filesystems • To allow access to files of other operating systems • Provide uniform ways of manipulating files, directories, and other objects • The kernel supports more than 40 filesystems.

  5. VFS

  6. VFS $cp /floppy/TEST /tmp/test Understanding the Linux Kernel 3rd Ed

  7. Filesystem Types • Disk-based filesystems • Storing files on nonvolatile media • Ext2/3, Reiserfs, FAT, and ISO9660 • Make use of block-oriented media • Network filesystems • Permit access to data on a computer attached to the local computer via a network

  8. Filesystem Types • All operations on files in this filesystem are carried out over a network connection • NFS, Coda, AFS, NCP(Novell) • Virtual filesystems (Special filesystems) • Generated in the kernel itself • Requires no storage space on any kind of hardware device • A simple interface to access the contents of some kernel data structure • /proc

  9. The Common File Model • Supports a uniform view of the objects in the filesystem. • A structure model consisting of all components that mirror a powerful filesystem • The model exists only virtually and must be adapted to each filesystem using a variety of objects with function pointers

  10. The Common File Model • Inode Object • Information about a specific file • Inode number • Store in filesystem control block • File Object • Interaction between an open file and a process • Only in kernel memory

  11. The Common File Model • Superblock Object • Information concerning a mounted filesystem • Store in filesystem control block • Dentry Object • Directory entry cache • Provide quick access to the results of a previous full lookup operation • Establish a link between a filename and its inode

  12. Inode Object linux/include/linux/fs.h Device file

  13. Inode lists • Each inode has a i_list to store the inode on a list • State of inode • inode_unused • Valid but no longer active inodes • inode_in_use • Used but unchanged inodes • i_count >0, i_nlink >0 • Dirty inodes • invalidate_inodes fs/inode.c

  14. Inode Operations linux/include/linux/fs.h

  15. File Objects linux/include/linux/fs.h

  16. File Operations linux/include/linux/fs.h

  17. Superblock Object linux/include/linux/fs.h

  18. Superblock operations linux/include/linux/fs.h

  19. Dentry Object linux/include/linux/dcache.h

  20. Dentry Operations linux/include/linux/dcache.h

  21. Interplay of VFS components

  22. Registering Filesystems linux/fs/filesystem.c

  23. Registering Filesystems linux/include/linux/fs.h

  24. Mount

  25. sys_mount linux/fs/namespace.c

  26. do_mount linux/fs/namespace.c

  27. do_new_mount

  28. do_new_mount linux/fs/namespace.c

  29. do_kern_mount linux/fs/super.c

  30. vfs_kern_mount linux/fs/super.c

  31. Mount rootfs

  32. mount_root linux/init/do_mounts.c

  33. mount_block_root linux/init/do_mounts.c

  34. do_mount_root linux/init/do_mounts.c

  35. Path lookup

  36. __link_path_walk linux/fs/namei.c

  37. __link_path_walk linux/fs/namei.c

  38. __link_path_walk linux/fs/namei.c

  39. do_lookup linux/fs/namei.c

  40. follow_link linux/fs/hostfs/hostfs_kern.c

  41. Opening Files

  42. sys_open linux/fs/open.c

  43. do_sys_open linux/fs/open.c

  44. Reading Files

  45. sys_read linux/fs/read_write.c

  46. vfs_read linux/fs/read_write.c

  47. Reference • Linux-2.6.29 • Professional Linux Kernel Architecture • Understanding the Linux Kernel • IBM developWorks kernel anatomy series

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