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File system interface (Directory and Disk Structure (Storage structure…

- - - - Search file
      - create file
      - delete file
      - list directory
      - rename file
      - traverse file system
  - - - All file in a directory
        
        Limited
        
        slow search
  - - - Each directory can be composed of directories or files
      - Two types of path
        
        Absolute
        
        begins in root and follows from there
        
        Relative
        
        Begins in current directory
  - - - n copies and an original shared copy
        
        allows for concurrency
        
        contains linking from copy to original
  - - - Need cycle detecting algorithm
        
        Garbage collection
- - - - Name
      - Identifier
      - Type
      - Location
      - Size
      - Protection
      - Time, date and user information
  - - - two steps
        
        Space must be found
        
        The new entry must be made
    - - System call with file name and information
        
        Must keep a writer pointer open
    - - System call that specifies name and where to put it
        
        Keeps a read pointer open
    - - Directory is searched
        
        current-file-position pointer is repositioned
        
        file seek
        
        logical
    - - Directory is searched, space is marked as free
    - - Keeping attributes
        
        removes content
    - - Table which contains all open files and their information
      - Includes an open count associated with each file to indicate how many processes have the file open.
    - - Pointer
      - count
      - Disk location
      - access rights
        
        Locking
        
        Prevents files from being deleted while in use or modified by multiple instances
        
        can be
        
        optional
        
        Mandatory
  - - - Usually split in name and type
      - UNIX uses magic number
        
        roughly indicates file type
  - - - Expects certain structure from certain file types
  - - - This helps physical search
- - - - Read_next()
  - - - Fixed-length logical sectors
        
        Relative block number
        
        offset
        
        We keep current position
  - - - Construction of index
        
        Database use this approach
- - - - Where the fs will be attached
  - - - if found
        
        mounted under Volume
  - - - A letter for each drive
        
        General graph under each letter
- - - - user level
      - group level
  - - - Machine containting files
        
        server
        
        specifies files on a directory level
      - Machine seeking access
        
        client
        
        security
        
        authentication
    - - Easier to manage than client server
        
        Unified access
        
        uses DNS
        
        host-name-to-network-address
        
        Username/password/user Id/ Group ID
      - yellow pages
        
        centralized information
        
        microsoft uses
        
        CIFS
        
        Active directory
        
        Grouping information
      - Industry moving
        
        LDAP
    - - metadata and corruption
      - Recovery mode
        
        State information is stored
        
        NFS
        
        Stateless dfs
    - - Manual
      - DFS
      - World Wide Web
  - - - Writes to an open file are visible to other users who have an open session
      - Users can share pointer of curren location
    - - OpenAFS
        
        Writes to an open file are not visible immeadiately
        
        Once a file is closed, chanfes are visible only in sessions starting
    - - Once a file is created it can't be modified
- - - - Users allowed for access types
      - Consequences
        
        tedious
        
        variable sized directory entry
        
        fix
        
        condensed version
        
        three types
        
        owner
        
        group
        
        everyone