Operating Systems: Practice 1

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Operating Systems Practice 1

• July 8, 2004

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Overview

• Administration
• Introduction
• File I/O
• Tips for Windows OS.
• Kernel and User modes

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Administration

• TA Alex Shulman
• E-mail shulmana_at_post.tau.ac.il
• Office Hours Thursday 1330 1430
• Location Shrieber 10
• Website
• http//www.cs.tau.ac.il/shulmana/
• http//www.cs.tau.ac.il/shulmana/courses/OS_Summe
  r_04/

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Exercises

• Weekly exercises
• Programming language C
• Singleton submission
• Assignments are 20 of total grade
• Final exam usually contains 1-2 question
  regarding the exercises.
• http//www.cs.tau.ac.il/shulmana/courses/ OS_Su
  mmer_04/Assignments.php

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Submission Guidelines

• Submit
• A printout of the exercise (to me or to box 251).
• An electronic version.
• Consult
• http//www.cs.tau.ac.il/shulmana/courses/ OS_S
  ummer_04/subgd.php

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Electronic Submission

• Location
• Directory os04c under your home directory.
• Subdirectory assign/
• E.g. Exercise 1 /os04c/assign1/
• E.g. Exercise 2 /os04c/assign2/
• Submit all .c files, .h files if and makefile.
• Do not touch or change the files you submit after
  the deadline due.

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Electronic Submission

• Permissionschmod 705 chmod 705 /software1
  chmod 705 /software1/assign1 chmod 705
  /software1/assign1/

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Electronic Submission

• File Headers
• / .....
• Full Name your-full-name
• Id No your-id
• User Name your-user-name
• Assignment No the-assignment-number
• ..... /

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References

• Operating Systems Sivan Toledo (Akademon, 2001)
• Operating System Concepts  Abraham Silberschatz,
  Baer Peter Galvin, Greg Gagne (John Wiley Sons,
  2001)
• Advanced Programming in the UNIX Environment  W.
  Richard Stevens (Addison Wesley, 1992)
• Understanding the Linux Kernel  Daniel P. Bovet,
  Marco Cesati (O'Reilly, 2000)

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Introduction
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Programs and processes

• A program is an executable file residing on disk.
  
• An executing instance of a program is called a
  process.
• Every process has a unique identifier, a
  nonnegative integer.

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Operating System
Operating System - coordinates access to physical
resources CPU, disk, I/O devices etc.
Services Memory management Protection Scheduling
File System and more
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Operating Systems

• Unix/Linux
• Windows
• Real-Time Operating Systems (e.g VxWorks,
  PSOS).
• Mainframes (e.g. VM of IBM)

Practices Scope
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File I/O
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Disk Access
Application Code
User Process
ltstdiogt etc.
C Library Functions
File System
File management
Segments
Kernel
Storage
Disk block
Driver
Disk1
Disk2
Disk3
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System Calls

• System Call is a request to the operating
  system to perform some activity.
• System calls are expensive. A system call
  requires the computer to
• save its state
• the operating system take control of the CPU
• the operating system performs some function
• the operating system save its state
• the operating system give control of the CPU back
  to you.

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System Calls

• File Manipulation
• Process Control
• Device Manipulation
• Information

Application Code
C Library Functions
User Process
System Calls
Kernel
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System Calls and Library Functions
Application Code
fopen,fclose, printf, fgetc, getchar,
User Process
C Library Functions
open, close, read, write, seek
File System
Kernel
. . .
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File descriptors

• Each file is referred to by file descriptors
  non negative integers.
• The kernel returns a file descriptor to the
  process, upon open or create commands.
• The file descriptor is used by other operation
  that refer to the file (e.g. read, write)

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Open/Close System Calls

• Open system call - is used to convert a pathname
  into a file descriptor.
• int open(const char pathname, int flags, int
  mode)
• Close system call - closes a file descriptor,
  so that it may be reused. Any locks held on
  the file it was associated with, and owned by the
  process, are removed.
• int close(int filedes)

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Unix Help

• man ltcommandgt
• man 1 General System Info.
• gt man 1 grep
• man 2 System Calls
• gt man 1 open
• man 3 Linux Programmer's Manual
• gt man 3 printf

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xman
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Read System Call

• Read system call- attempts to read up to
  count
• bytes from file descriptor fd into the buffer
• starting at buf.
• int read(int fd, void buf, int count)
• Return Value
• On success, the number of bytes read is
  returned.
• The file position is advanced by this number.
• The returned number may be smaller than the
  number of bytes requested .

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Write System Call

• Write system call-writes up to count bytes to
  the file
• referenced by the file descriptor fd from the
  buffer
• starting at buf.
• int write(int fd, void buf, int count)
• Return Value
• On success, the number of bytes written is
  returned. The returned number may be smaller than
  the number of bytes requested .

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Standard Input, Output and Error
Unix shells associate file descriptor0 standard
input, 1 standard output, 2 standard error

• include ltfcntl.hgt
• int main(void)
• char c
• while (read(0, c, 1) 1) write(1, c, 1)
  return 0

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Lseek System Call

• Reposition the file offset.
• File offset a non-negative integer that
  measures the number of bytes from the beginning
  of the file.
• Read and write operations start at the current
  file offset and increment it by the number of
  bytes read or written.
• By default, this offset is initialized to 0 when
  a file is opened, unless the O_APPEND option is
  specified.

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lseek

• off_t lseek(int filedes, off_t offset, int
  whence)
• Returns new file offset if OK, -1 on error.
• The interpretation of the offset depends on the
  value
• of the whence argument
• SEEK_SET offset bytes from beginning of file
• SEEK_CUR current value offset
• SEEK_END size of file offset

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Potential Problems
Process 1
Process 2
1. Seek 3. Read
2. Seek 4. Read
File
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File system calls exercise 1

• Implementing a Windows CopyFile procedure.
• The program should use the system calls described
  except for lseek.
• Copying should be performed using a buffer size
  of n bytes.

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CopyFile Function
lpExistingFileName - the name of an existing
file. lpNewFileName - the name of the new file.
bFailIfExists - If TRUE and the new file
exists, the function fails. If FALSE and the new
file exists, the function overwrites the existing
file and succeeds.
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MSDN Help
http//msdn.microsoft.com/
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SDK

• Microsoft Windows Software Development Kit
  (SDK).
• An Application Programming Interface (API)
  designed for anyone who wants to develop a
  Windows Media.
• Allows to programmatically manage a Windows Media
  server to send digital media content to clients
  on both unicast and multicast-enabled networks.

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Windows Tips

• include ltwindows.hgt
• include ltstdio.hgt
• int main(int argc, LPTSTR argv)
• .

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Windows Data Types

• LPVOID a pointer to void.
• LPTSTR - a 32-bit pointer to a character string.
• DWORD - a 32-bit unsigned integer
• CHAR - an 8-bit Windows (ANSI) character.
• All Win32 objects are identified by variables of
  type
• HANDLE, and a single generic CloseHandle
• function applies to most objects.

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Error Codes

• Windows System error codes, as DWORDs, can be
  obtained at any point using GetLastError.
• Unix Global variable errno provides information
  about the Unix function call failure.
• gt man errno

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Kernel Monitoring