Ex1: inode
 inode structure:
  -- metadata:
      Size of a file
      Owner's user id
      Permission:
        File type: directory, regular file or soft link.
        Access permission: how different users can access it.
      Timestamps: Access time, modification time and change time.
      Link count: How many files are associated with this inode.
  -- Pointers:
      Direct Pointer 1  --> data block
      Direct Pointer 2  --> data block
      ...
      Direct Pointer 12 --> data block
      Single Indirect Pointer --> indirect block:
                                  Pointer --> data block
                                  Pointer --> data block
                                  ...
                                  Pointer --> data block
      Double Indirect Pointer --> indirect block:
                                  Indirect Pointer --> indirect block:
                                                       Pointer --> data block
                                                       Pointer --> data block
                                                       ...
                                                       Pointer --> data block
                                  ...
                                  Indirect Pointer --> ditto
      Triple Indirect Pointer --> ...
 Question: Which factors determine many pointers one indirect block can hold?
 Question: Given this structure, can we have file of any size?
 Question: Say we have 512-byte block, 4-byte pointer, 12 direct pointers,
     1 single indirect pointer, 1 double, and 1 triple. How many regular
     files (no links) can we have? What is the maximum size of a file?

Ex2: Directories
  In a terminal, we first type:
  $ cd /

  Note that / is a file.
  Say we have the file *content* to '/' as:
      [name, i-number]
      <bin, 1021>
      <dev, 1022>
      <etc, 1023>
      <proc, 1024>
      ...
  Briefly describe the actions when we type:
  $ ls bin

Ex3: Problem for inodes and directories
  Consider a very simple file system for a tiny disk. Each sector on the disk
  holds 2 integers, and all data blocks, indirect blocks, and inodes are 1 disk
  sector in size (each contains 2 integers). All files stored on disk are
  interpreted as directories by the file system (there are no "data files"). The
  file system defines the layout for the following data types on disk:
      -- inode = 1 pointer to a data block + 1 pointer to indirect block
      -- indirect block = 2 pointers to data blocks
      -- directory = a regular file containing zero or more pairs of integers;
          the first integer of each pair is a file name and the second is the
          file's inumber

  The value "99" signifies a null pointer when referring to a disk block address
  or directory name. An empty directory has one disk block with the contents
  "99   99". The inumber for root directory is "/" is 0.

  The following data are stored on disk:

  inode array:
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 |11 |12 |13 |14 |15 |
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
  |10 | 7 |   | 8 |   |   | 3 |   |   |   |   |   |   |   |   |   |
  | 6 |99 |   |99 |   |   |99 |   |   |   |   |   |   |   |   |   |
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

  disk blocks:
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 |11 |12 |13 |14 |15 |
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
  |   |32 |   |96 |   |   | 1 |99 |99 |   |57 |   |   |   |   |   |
  |   | 3 |   | 1 |   |   |99 |99 |99 |   | 6 |   |   |   |   |   |
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

  1. How many entries can appear in a maximum-sized directory?
      (Each entry is a pair of integers)

  2. List all directories stored on this disk (full path names) along with the
      names of the files stored in each directory.

      +----------+----------+-----------------+-------------+---------------+
      | path     | i-number | indirect blocks | data blocks |    subdirs    |
      +----------+----------+-----------------+-------------+---------------+
      | /        |          |                 |             |               |
      +----------+----------+-----------------+-------------+---------------+
      |          |          |                 |             |               |
      +----------+----------+-----------------+-------------+---------------+
      |          |          |                 |             |               |
      +----------+----------+-----------------+-------------+---------------+
      |          |          |                 |             |               |
      +----------+----------+-----------------+-------------+---------------+
      |          |          |                 |             |               |
      +----------+----------+-----------------+-------------+---------------+

  3. Modify the above data structures to add an empty directory called "87"
      to directory "/"

Ex4: Hard/soft links
    pwd data:           /bin data
    +-----------+       +-----------+
    |           |       | cp - 1001 |
    +-----------+       +-----------+
    |...        |       |...        |

    inode 1001: link count: 1

    What will the above look like after we type? Any other changes else where?
    $ ln /bin/cp cc

    What will the above look like after we type? Any other changes else where?
    $ ln -s /bin/cp cc