CSCI 4061 HW08: mmap() / Basic Signals and Handlers

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                            HW 08 QUESTIONS
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- Name: (FILL THIS in)
- NetID: (THE kauf0095 IN kauf0095@umn.edu)

Write your answers to the questions below directly in this text file.
HW quiz questions will be related to the questions in this file.


PROBLEM 1: Binary File Format w/ Read
=====================================

A
~

  Compile all programs in the directory `binfiles/' with the provided
  `Makefile'.  Run the command
  ,----
  | ./make_dept_directory cse_depts.dat
  `----

  to create the `cse_depts.dat' binary file. Examine the source code for
  this program along with the header `department.h'.
  - What system calls are used in `make_dept_directory.c' to create this
    file?
  - How is the `sizeof()' operator used to simplify some of the
    computations in `make_dept_directory.c'?
  - What data is in `cse_depts.dat' and how is it ordered?


B
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  Run the `print_department_read' program which takes a binary data file
  and a department code to print.  Show a few examples of running this
  program with the valid command line arguments. Include in your demo
  runs that
  - Use the `cse_depts.dat' with known and unknown department codes
  - Use a file other than `cse_depts.dat'


C
~

  Study the source code for `print_department_read' and describe how it
  initially prints the table of offsets shown below.
  ,----
  | Dept Name: CS Offset: 104
  | Dept Name: EE Offset: 2152
  | Dept Name: IT Offset: 3688
  `----
  What specific sequence of calls leads to this information?


D
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  What system call is used to skip immediately to the location in the
  file where desired contacts are located? What arguments does this
  system call take? Consult the manual entry for this function to find
  out how else it can be used.


PROBLEM 2: mmap() and binary files
==================================

  An alternative to using standard I/O functions is "memory mapped"
  files through the system call `mmap()'. The program
  `print_department_mmap.c' provides the functionality as the previous
  `print_department_read.c' but uses a different mechanism.


(A)
~~~

  Early in `print_department_mmap.c' an `open()' call is used as in the
  previous program but it is followed shortly by a call to `mmap()' in
  the lines
  ,----
  |   char *file_bytes =
  |     mmap(NULL, size, PROT_READ, MAP_SHARED,
  |          fd, 0);
  `----
  Look up reference documentation on `mmap()' and describe some of the
  arguments to it including the `NULL' and `size' arguments. Also
  describe its return value.


(B)
~~~

  The initial setup of the program uses `mmap()' to assign a pointer to
  variable `char *file_bytes'.  This pointer will refer directly to the
  bytes of the binary file.

  Examine the lines
  ,----
  |   ////////////////////////////////////////////////////////////////////////////////
  |   // CHECK the file_header_t struct for integrity, size of department array
  |   file_header_t *header = (file_header_t *) file_bytes; // binary header struct is first thing in the file
  `----

  Explain what is happening here: what value will the variable `header'
  get and how is it used in subsequent lines.


(C)
~~~

  After finishing with the file header, the next section of the program
  begins with the following.
  ,----
  |   ////////////////////////////////////////////////////////////////////////////////
  |   // SEARCH the array of department offsets for the department named
  |   // on the command line
  | 
  |   dept_offset_t *offsets =           // after file header, array of dept_offset_t structures
  |     (dept_offset_t *) (file_bytes + sizeof(file_header_t));
  | 
  `----

  Explain what value the `offsets_arr' variable is assigned and how it
  is used in the remainder of the SEARCH section.


(D)
~~~

  The final phase of the program begins below
  ,----
  |   ////////////////////////////////////////////////////////////////////////////////
  |   // PRINT out all personnel in the specified department
  |   ...
  |   contact_t *dept_contacts = (contact_t *) (file_bytes + offset);
  `----
  Describe what value `dept_contacts' is assigned and how the final
  phase uses it.


PROBLEM 3: `birth_death.c'
==========================

A
~

  Compile `circle_of_life.c' to the program `circle_of_life' and run
  it. Examine the results and feel free to terminate execution
  early. Examine the source code if desired though it is merely a
  print/sleep loop.

  Compile `birth_death.c' to the program `birth_death'. This program is
  invoked with two arguments, another program name and a "lifetime"
  which is an integer number of seconds. Run it like
  ,----
  | $> ./birth_death ./circle_of_life 4
  `----

  and show the output below.


B
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  Examine the source code for `birth_death.c' and determine the system
  call the parent program (`birth_death') uses to send signals to the
  child program. Paste this line below and explain which signal is being
  sent.


C
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  `birth_death.c' waits for a child to finish then outputs what signal
  caused it to be terminated if that was the cause of death. Paste the
  lines of code which determine if a child was terminated due to a
  signal below and mention the macros used for this purpose.


D
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  Compile the program `no_interruptions.c' and run it with
  `birth_death'. Show your results below.

  Note that you may need to send signals to `no_interruptions' to
  forcibly end it. The `pkill' command is useful for this as in
  ,----
  | pkill no_inter        # send TERM signal to proc name matching "no_inter"
  | pkill -KILL no_inter  # send KILL signal to proc name matching "no_inter"
  `----


E
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  Examine the `no_interruptions.c' code and describe how it is able to
  avoid being killed when receiving the interrupt and TERM signals. Show
  the lines of code used to accomplish this signal handling.