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January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma
The Process API,
Limited Direct Execution
Wes J. Lloyd
Institute of Technology
University of Washington - Tacoma
TCSS 422: OPERATING SYSTEMS
Feedback from 1/
Homework 0 Questions
Class Activity 1
Operating system design goals
Chapter 5: C Linux Process API
Chapter 6: Limited Direct Execution
Virtualizing the CPU
January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. OBJECTIVES
Please complete the Virtual Machine Survey if wanting
an Institute of Technology hosted Ubuntu 16.04 VM
https://goo.gl/forms/XAxxuZtut5o707Ip January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. VIRTUAL MACHINE SURVEY
What are fork() and exec() used for?
fork() - splits a running process into two process
It’s like CLONING a process
exec() is used to “run” another program from an existing process
Can control: standard in (stdin)
standard out (stdout)
standard err (stderr)
Capture input/output to the external program.
January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. SELECTED FEEDBACK FROM 1/
What are examples of when to launch new processes?
Memory is not shared (heap or stack)
Code is shared
Fork + Exec heap, stack, code not shared
And launch new threads?
Memory is shared (heap and code)
Not stack based memory
January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. FEEDBACK - 2 What are these three different states? RUNNING READY BLOCKED January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. FEEDBACK - 3
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Redirect s tdout
./myscript.sh > output.txt
Redirect s tdout and std err
./myscript.sh > output.txt 2> output.err
Redirect s tdout and stderr to s ame file
./myscript.sh > alloutput.txt 2>&
./myscript.sh > alloutput.txt 2>alloutput.txt
January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. LINUX OUTPUT REDIRECTION
Do I have to read the book chapter carefully or just skim
through before coming to class?
Can a sample format submission be provided for
assignment 0?
You went too fast
Please interrupt!
Throw tomatoes
January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. FEEDBACK - 5 CH. 2: INTRODUCTION TO OPERATING SYSTEMS January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3.
ABSTRACTING THE HARDWARE
Makes programming code easier to write
Automate sharing resources – save programmer burden
PROVIDE HIGH PERFORMANCE
Minimize overhead from OS abstraction
(Virtualization of CPU, RAM, I/O)
Share resources fairly
Attempt to tradeoff performance vs. fairness consider
priority
PROVIDE ISOLATION
User programs can’t interfere with each other’s virtual
machines, the underlying OS, or the sharing of resources
January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. SUMMARY: OPERATING SYSTEM DESIGN GOALS
RELIABILIT Y
OS must not crash, 24/7 Up-time
Poor user programs must not bring down the system:
Blue Screen
Other Issues:
Energy-efficiency
Security (of data)
Cloud: Virtual Machines
January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. SUMMARY: OPERATING SYSTEM DESIGN GOALS - 2 ABSTRACTING THE HARDWARE PROVIDE HIGH PERFORMANCE PROVIDE ISOLATION RELIABILIT Y January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. OPERATING SYSTEM DESIGN GOALS
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January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3. EXEC EXAMPLE - 2 … execvp(myargs[ 0 ], myargs); // runs word count } else^ printf("this { shouldn’t print out");// parent goes down this path (main) int printf("hello, wc = wait(NULL); I am parent of %d (wc:%d) (pid:%d)\n", }^ rc, wc, (int)^ getpid()); }^ return^0 ; prompt> hello world ./p3 (pid:29383) hello, 29 107 I 1030 am childp3.c (pid:29384) hello, prompt> I am parent of 29384 (wc:29384) (pid:29383) January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3. EXEC WITH FILE REDIRECTION (OUTPUT) #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h> #include <fcntl.h> #include <sys/wait.h> int main(int argc, char *argv[]){ int if (rc <rc = fork(); 0 ) { // fork failed; exit fprintf(stderr, exit( 1 ); "fork failed\n"); } else if close(STDOUT_FILENO); (rc == 0 ) { // child: redirect standard output to a file open("./p4.output", O_CREAT|O_WRONLY|O_TRUNC, … S_IRWXU); January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3. FILE MODE BITS S_IRWXU read, write, execute/search by owner S_IRUSR read permission, owner S_IWUSR write permission, owner S_IXUSR execute/search permission, owner S_IRWXG read, write, execute/search by group S_IRGRP read permission, group S_IWGRP write permission, group S_IXGRP execute/search permission, group S_IRWXO read, write, execute/search by others S_IROTH read permission, others S_IWOTH write permission, others January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3. EXEC W/ FILE REDIRECTION (OUTPUT) - 2 … // now exec "wc"... char myargs[ *myargs[ 0 ] = strdup("wc"); 3 ]; // program: "wc" (word count) myargs[ myargs[ 12 ]] = strdup("p4.c");= NULL; // argument:// marks end fileof array to count } else^ execvp(myargs[ { 0 ],^ myargs);^ // parent// runs goes down this path (main)^ word^ count }^ int^ wc^ = wait(NULL); }^ return^0 ; prompt> ./p4 prompt> cat p4.output 32 109 prompt> 846 p4.c January 10, 2018 TCSS422: Operating Systems [Winter 2018] Institute of Technology, University of Washington - Tacoma L3. CH. 6: LIMITED DIRECT EXECUTION January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3.
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How does the CPU support running so many jobs
simultaneously?
Time Sharing
Tradeoffs:
Performance
Excessive overhead
Control
Fairness
Security
Both HW and OS support
is used
January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3.
VIRTUALIZING THE CPU
What if programs could directly control the CPU / system?
January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3.
COMPUTER BOOT SEQUENCE:
OS WITH DIRECT EXECUTION
OS Program
1. Create entry for process list
2. Allocate memory for
program
3. Load program into memory
4. Set up stack with argc /
argv
5. Clear registers
6. Execute call main()
9. Free memory of process
10. Remove from process list
7. Run main()
8. Execute return from main()
Without limits on running programs,
the OS wouldn’t be in control of anything
and would “just be a library”
With direct execution:
How does the OS stop a program from running, and switch
to another to support time sharing?
How do programs share disks and perform I/O if they are
given direct control? Do they know about each other?
With direct execution, how can dynamic memory structures
such as linked lists grow over time?
January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3.
DIRECT EXECUTION - 2
Too little control:
No security
No time sharing
Too much control:
Too much OS overhead
Poor performance for compute & I/O
Complex APIs (system calls), difficult to use
January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3.
CONTROL TRADEOFF
January 10, 2018 TCSS422: Operating Systems [Spring 2017] Institute of Technology, University of Washington - Tacoma L3.
CONTEXT SWITCHING OVERHEAD
QUESTIONS
