File Systems Intro

Notes

• A file is a collection of data recorded on secondary storage.
• It is basic to the operation of a computer.
• A file normally consists of
  • Blocks of data
  • A block of information
    • Size
    • Various times
    • Possibly a file type
    • Owner and access information.
• File systems normally support
  • Opening and Closing a file.
  • Reading and writing to a file
  • seeking a position within a file.
  • file deletion and truncation
• The interface between program/os/file
  • I am going with Kerrisk chapter 55.4
  • Each process has an open file table.
    • A pointer to the system wide file table.
    • Some information (very little, cloexec flag)
  • The kernel maintains a table of open files
    • The current offset (any process with that open file will referer to the same place in the file)
    • A set of status flages
      • open status (r, w, rw)
      • OS related (signal ( information)
      • A pointer to the i-node table in the kernel.
  • The kernel maintains a list of open i-nodes
    • File types and permissions
    • File locks
    • The inode number and file system.
  • from Kerrisk
• As you know, linux maitains the file system as a tree
  • File systems are mounted on this tree.
  • That is a lie, this is actually a digraph.
• Hard links
• soft lnks
• Directories
  • As we will see soon, linux does not keep the file name at the file leve.
  • Directories are simply well formatted files.
  • readdir returns a directory entry
    • reference
  • The Virtual File System
    • An interface for file systems operations.
    • A definition of functions
    • An interface implementation
  • Operations
    • open
    • read
    • write
    • lseek
    • close
    • truncate
    • stat
    • mount/umount
    • mmap
    • mkdir
    • link
    • unlink
    • symlink
    • rename.