DOCSLIB.ORG

Process Manager Ext2fs Proc Devfs Process Management Memory Manager Scheduler Minix Nfs Msdos Memory Management Signaling

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Process Manager Ext2fs Proc Devfs Process Management Memory Manager Scheduler Minix Nfs Msdos Memory Management Signaling Embedded Systems Prof. Myung-Eui Lee (A-405) [email protected] Embedded Systems 1-1 KUT Linux Structure l Linux Structure proc1 proc2 proc3 proc4 proc5 procn User Space System Call Interface Filesystem Manager Process Manager Ext2fs proc devfs Process Management Memory Manager Scheduler minix nfs msdos Memory Management Signaling Buffer Cache Kernel Space Device Manager Network Manager char block Ipv6 ethernet Console KBD SCSI CD-ROM PCI network ….. Device Interface dev1 dev2 dev3 dev4 devn Embedded Systems 1-2 KUT Linux Structure l Linux Structure Applications: Graphics UI, Compilers, Media player UI Text UI = Shell: sh, csh, ksh, bash, tcsh, zsh Compiler libraries (libc.a) API System Shared Libraries (System Call Interface) Memory File Process management management management Kernel Device Drives BIOS Computer Hardware Embedded Systems 1-3 KUT System Call Interface Standard C Lib. System Call C program invoking printf() library call, API – System call – OS Relationship which calls write() system call ar –t /usr/lib/libc.a | grep printf /usr/src/linux-2.4/arch/i386/kernel/entry.S Embedded Systems 1-4 KUT System Call l System calls define the programmer interface to Linux system » Interface between user-level processes and hardware devices u CPU, memory, disks etc. » Make programming easier u Let kernel take care of hardware-specific issues » Increase system security u Let kernel check requested service via system call » Provide portability u Maintain interface but change functional implementation l Roughly five categories of system calls in Linux » Process control » File management * 288 system calls » Device management refer to slide #6 » Information maintenance » Communication Embedded Systems 1-5 KUT System Call l Invoked by executing int or swi instruction » CPU switches to kernel mode & executes a kernel function x86 : movl %eax, 2 ; system call number int $0x80 ARM : swi 2 ; system call number l Linux files relating to system call » /usr/src/linux-2.4/arch/i386/kernel/entry.S x86 host #408 /pxa270/kernel/linux-2.6…/arch/arm/kernel/calls.S ARM target #17 u System call and low-level fault handling routines u ENTRY(sys_call_table) » /usr/src/linux-2.4/include/asm-i386/unistd.h x86 host /pxa270/kernel/linux-2.6…/include/asm-arm/unistd.h ARM target u System call numbers and macros Embedded Systems 1-6 KUT ARM System Call l ARM System Call Example An example to write a short file on disk SWI_Exit EQU 0x01 SWI_Write EQU 0x04 SWI_Open EQU 0x05 SWI_Close EQU 0x06 write_only EQU 4 ; mode 4 = open to write ENTRY ; mark first instruction to execute start ADR r0, filename ; r0 points to string MOV r1, #write_only ; file attribute for write only SWI SWI_Open ; open a file for writing MOV r5, r0 ; save file-handle in r5 ADR r1, string ; point to a string MOV r2, #14 ; 14 characters long SWI SWI_Write ; write to file MOV r0, r5 ; restore file-handle SWI SWI_Close ; close the file SWI SWI_Exit filename = "test.txt",0 string = "Hello World!",&0a,&0d END Embedded Systems 1-7 KUT System Call l System Call Handling kernel user task ENTRY(system_call) /* arch/i386/kernel/entry.S */ main() SAVE_ALL { . …. … fork() idt_table call *SYMBOL_NAME(sys_call_table)(,%eax,2) } 0x0 divide_error() …. debug() ret_from_sys_call (schedule, signal, bh_active, nmi() nested interrupt handling) libc.a . sys_call_table … …. fork() { …. 1 sys_exit() movl %eax, 2 0x80 int $0x80 system_call() 2 sys_fork() sys_fork() …. …. sys_read () } 3 /* arch/i386/kernel/process.c */ . … 4 sys_write () /* kernel/fork.c */ …. Embedded Systems 1-8 KUT Process l Program » Structured set of commands stored in an executable file on a file system » Executed to create a process l Process » Program running in memory and on the CPU (active program) » Modern systems allow ‘multiprogramming’ (i.e., several processes exist concurrently) » Each process requires an allocation of cpu time, in order to make forward progress » The OS must do ‘scheduling’ of cpu time » Each process also needs the use of other system facilities (memory, files, devices) » The terms job (batch system) and process is almost used interchangeably Embedded Systems 1-9 KUT Process l A process includes Process in memory » text section : program » stack » data section » heap l User process » Process begun by a user that runs on a terminal (tty) l Daemon process » System process » Not associated with a terminal l Process ID (PID) top, ps -el » Unique identifier assigned to every process as it begins » Processes are identified by their process identifier, an integer Embedded Systems 1-10 KUT Process l Child processes » Refers to a process that was started by another process (parent process) l Parent processes » Process that has started other processes (child processes) l Parent Process ID (PPID) ps -el » The PID of the parent process that created the current process l Processes communicate via pipes (IPC) » Queues of bytes between two processes that are accessed by a file descriptor Embedded Systems 1-11 KUT Process l Process System Call » Creation : fork system call creates new process u the process that calls fork() is parent, the new process is child u fork() is calling sys_fork() → do_fork() in /kernel/fork.c u “cloning flags” : man clone /usr/src/linux-2.4/include/linux/sched.h #39 » Execution : exec system call is used after a fork to execute the process » Exit : exit terminates process and free all resources u Calling exit() → sys_exit() → do_exit () explicit kernel/exit.c u The child is turned into a zombie process until the parent makes the call to wait Refer to → When a process finishes execution, it will have an exit status to Slide #26 report to its parent process. Because of this last little bit of information, the process will remain in the operating system’s process table as a zombie process. indicating that it is not to be scheduled for further execution, but that it cannot be completely removed (and its process ID cannot be reused) » Wait : A parent may wait for a child process to terminate, and return its termination status Embedded Systems 1-12 KUT Process l Process termination » Voluntary termination 1. Returning to the main() function (implicit) 2. Calling exit() (explicit) » Involuntary termination 1. An exception might be raised during its kernel mode execution 2. The process might have received the SIGABRT or other termination signal » Termination process state 1. the parent is alive : zombie process 2. the parent is dead : orphan process An orphan process is a process that is still executing, they do not become zombie processes; instead, they are adopted(inherited) by init process (PID 1) l Task » Another name for a process is a task, and Linux kernel internally refers to processes as tasks » Generally refer to a process from the kernel’s point of view Embedded Systems 1-13 KUT Task » As seen by a process running under Linux Process and Tasks u The kernel is a provider of services u Individual processes exist independently alongside each other and cannot affect each other directly u Each process’s own area of memory is protected against modification by other processes » The internal viewpoint of a running Linux u Only one program (OS) is running on the computer, can access all the resource u The various tasks are carried out by co-routines u An error in the kernel programming can block the entire system Embedded Systems 1-14 KUT Process Control Block (PCB) l Information associated with each process l type sturcture task_struct ; line 382 (target:528) » /usr/src/linux-2.4/include/linux/sched.h Process state Unique process identifier Memory-management information File system information Signal information Program counter CPU registers CPU scheduling information (e.g., priority) Accounting information I/O status information Pointers to other control blocks Embedded Systems 1-15 KUT Process Control Block (PCB) l task_struct prev_task next_task pid gid task-name process task-state task-priority execution aspects processor register-values (EIP, ESP, EFLAGS, etc) memory-map open files resource ownership terminal aspects timers signal-handlers Embedded Systems 1-16 KUT Process Control Block l task_struct struct task_struct { volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */ unsigned long flags; /* per process flags */ mm_segment_t addr_limit; /* thread address space: 0-0xBFFFFFFF for user-thead 0-0xFFFFFFFF for kernel-thread */ mm_struct struct exec_domain *exec_domain; task_struct long need_resched; pid = 5 long counter; long priority; mm /* SMP and runqueue state */ slg signal_struct struct task_struct *next_task, *prev_task; struct task_struct *next_run, *prev_run; files ... /* task state */ /* limits */ files_struct /* file system info */ /* ipc stuff */ /* tss for this task */ … /* open file information */ /* memory management info */ /* signal handlers */ ... }; Embedded Systems 1-17 KUT Thread l Thread of execution = Thread l The object of activity within the process l Each thread includes a unique program counter, process stack, and set of processor registers l The kernel schedules individual threads, not process l Linux does not differentiate between threads and processes : a thread is just a special kind of process l A process has two distinct aspects » Its ‘execution’ (forward progression of states) » Its ‘ownership’ (share of system’s resources) » The word ‘thread’ refers to the execution aspect of a process (i.e., the entity which gets ‘scheduled’ by an Operating System for a share of the available cpu time) Embedded Systems 1-18 KUT Thread l Multi-threading » It is possible
Load more

Recommended publications
  • Tutorials Point, Simply Easy Learning
    Tutorials Point, Simply Easy Learning UML Tutorial Tutorialspoint.com UNIX is a computer Operating System which is capable of handling activities from multiple users at the same time. Unix was originated around in 1969 at AT&T Bell Labs by Ken Thompson and Dennis Ritchie. This tutorial gives an initial push to start you with UNIX. For more detail kindly check tutorialspoint.com/unix What is Unix ? The UNIX operating system is a set of programs that act as a link between the computer and the user. The computer programs that allocate the system resources and coordinate all the details of the computer's internals is called the operating system or kernel. Users communicate with the kernel through a program known as the shell. The shell is a command line interpreter; it translates commands entered by the user and converts them into a language that is understood by the kernel. Unix was originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna. There are various Unix variants available in the market. Solaris Unix, AIX, UP Unix and BSD are few examples. Linux is also a flavour of Unix which is freely available. Several people can use a UNIX computer at the same time; hence UNIX is called a multiuser system. A user can also run multiple programs at the same time; hence UNIX is called multitasking. Unix Architecture: Here is a basic block diagram of a UNIX system: 1 | P a g e Tutorials Point, Simply Easy Learning The main concept that unites all versions of UNIX is the following four basics: Kernel: The kernel is the heart of the operating system.
    [Show full text]
  • Processes in Linux/Unix
    Processes in Linux/Unix A program/command when executed, a special instance is provided by the system to the process. This instance consists of all the services/resources that may be utilized by the process under execution. • Whenever a command is issued in unix/linux, it creates/starts a new process. For example, pwd when issued which is used to list the current directory location the user is in, a process starts. • Through a 5 digit ID number unix/linux keeps account of the processes, this number is call process id or pid. Each process in the system has a unique pid. • Used up pid’s can be used in again for a newer process since all the possible combinations are used. • At any point of time, no two processes with the same pid exist in the system because it is the pid that Unix uses to track each process. Initializing a process A process can be run in two ways: 1. Foreground Process : Every process when started runs in foreground by default, receives input from the keyboard and sends output to the screen. When issuing pwd command $ ls pwd Output: $ /home/geeksforgeeks/root When a command/process is running in the foreground and is taking a lot of time, no other processes can be run or started because the prompt would not be available until the program finishes processing and comes out. 2. Backround Process : It runs in the background without keyboard input and waits till keyboard input is required. Thus, other processes can be done in parallel with the process running in background since they do not have to wait for the previous process to be completed.
    [Show full text]
  • CENG251: Assignment #5
    Out: March 30, 2021 Due: Wed Apr 14, 2021 There are 30 marks. Please keep and submit a time log to account for what you’ve done. CENG251: Assignment #5 Part I: C Language Features (8 marks) In class we demonstrated re-entrant code by comparing the use of ctime vs ctime_r. We showed that ctime always returned the same memory location and that ctime_r avoided this problem by passing the memory to be filled which was then returned with a different result; Write a single small C program that 1. Demonstrates that getpwuid and getpwnam are not reentrant by calling each of these twice with different valid arguments and displaying the return address and the content of the passwd structure returned. Prepare your output string using fmemopen and then writing the output to a string using a file pointer before writing the string to the terminal. An example of using fmemopen can be found in the example program stringIODemo.c (3) 2. Continue the program and call getpwuid_r and getpwnam_r with correct arguments. Prepare your output string using sprintf and then display the string to the terminal. Examples of long structured format strings can be seen in the example program stringIODemo.c (3) 3. In ctimeDemo.c we demonstrated the use of strdup to preserve the result of ctime from one function call to the next. Use malloc and memcpy to do the same for getpwuid and show that this worked displaying the values from the copy. (2) Part II: Signals (8 marks) The following exercises should be done as a single program.
    [Show full text]
  • Unit-Iv Process,Signals and File Locking
    UNIT-IV PROCESS, SIGNALS AND FILE LOCKING III-I R14 - 14BT50502 PROCESS: When you execute a program on your UNIX system, the system creates a special environment for that program. This environment contains everything needed for the system to run the program as if no other program were running on the system. Whenever you issue a command in UNIX, it creates, or starts, a new process. When you tried out the ls command to list directory contents, you started a process. A process, in simple terms, is an instance of a running program. When you start a process (run a command), there are two ways you can run it − Foreground Processes Background Processes FOREGROUND PROCESSES: By default, every process that you start runs in the foreground. It gets its input from the keyboard and sends its output to the screen. Example: $ls ch*.doc When a program is running in foreground and taking much time, we cannot run any other commands (start any other processes) because prompt would not be available until program finishes its processing and comes out. BACKGROUND PROCESSES: A background process runs without being connected to your keyboard. If the background process requires any keyboard input, it waits. The advantage of running a process in the background is that you can run other commands; you do not have to wait until it completes to start another! The simplest way to start a background process is to add an ampersand (&) at the end of the command. Example: $ls ch*.doc & PROCESS IDENTIFIERS: The process identifier – normally referred to as the process ID or just PID, is a number used by most operating system kernels such as that of UNIX, Mac OS X or Microsoft Windows — to uniquely identify an active process.
    [Show full text]
  • Processes – CSC252
    Processes – CSC252 PROF. EARL Some slides adopted from Dr. John Carelli and Dr. Lisa Frye User • Programs that the user interacts with User vs or launches themselves Kernel Kernel • Provides services to user space. Space Manages hardware and resources for multiple users. User processes access this space through system calls Hardware Processes https://goo.gl/images/381BdN Processes A single process is the execution of command by the Linux Kernel Every process (besides init) has a Process ID (PID) and Parent Process ID (PPID) Processes are “spawned” from another System Calls Allow a program in user space to interact with the kernel fork() – Allows for a process to create a new sub-process (A child process) The PPID of the new process, would be the PID of the process that called fork() exec() – Execute a new command replace the process with the new one. Sessions The lifetime a user login process When a user logins into a linux machine, a new shell process is created job – A command pipeline ; - Separate Commands & - Run the command in the background Basic Process Commands history – log of past commands jobs – List of currently running jobs kill – Terminal a process fg,bg – Move a process to the foreground/background ps – List processes top – View top running processes uptime – View how long system has been running free – View available memory (RAM) pstree – Show process tree nohup – run command immune to hangups Review the student presentations as posted on D2L (except for ps) The Process Table Data structure that exists in Kernel Space Contains the following: Process ID Process Owner Process Priority Environment variables for each process The Parent Process Location of its code, data, stack, and user area Pending Signals The ps command UNIX command that allows you to view information from the process table.
    [Show full text]
  • Tutorial 2 : Process Management
    Tutorial 2 : Process Management August 20, 2019 Objective : • This assignment is intended to learn how to create, work with and ma- nipulate processes in Linux. You are expected to refer to the text book and references mentioned in the course website befor you start the lab. Some sample codes for process creation using fork system call have been provided for your reference. Instructions • You are expected to run all the sample codes provided in the Helpful Re- sources section. It will help you understand how OS virtualizes CPU and memory. Some of the codes are related to process creation and execution using Unix based system calls such as fork,exit,wait and exec Tutorials 1. Tut1 : Memory Virtualization : Physical memory model presents Memory as an array of bytes. The data stored at an address of memory can be read by providing the address of the location wehere the data resides. Similarly, while writing data to any address of a memory, one needs to specify the address for writing as well as the data to be written to the given address. Memory is accessed all the time when a program is running. A program keeps all of its data structures in memory, and accesses them through various instruction. In- structions themeselves reside in the memory which have to be fetched. Instructions : Execute the code mem.c from the Helpful Resources sec- tion. Make sure to include the common.h file in the same folder as the mem.c. To execute use the following commands : gcc mem.c ./a.out ox200000 The program does a couple of things.
    [Show full text]
  • Exec(“/Bin/Ls”) : Overwrites the Memory Code Image with Binary from /Bin/Ls and Execute
    Assignment 1 Υπεύθυνοι βοηθοί: Ειρήνη Δέγκλερη ( [email protected] ) Ηλίας Παπαδόπουλος ( [email protected] ) System Calls ■ If a process is running a user program in user mode and needs a system service, such as reading data from a file, it has to execute a trap instruction to transfer control to the operating system. Application – USER SPACE System Call KERNEL SPACE System Calls A system call is a request for service that a program makes of the kernel. The service is generally something that only the kernel has the privilege to do, such as doing I/O. Fork() ■ Fork creates a new process (child process). – It creates an exact duplicate of the original process, including all the file descriptors, registers—everything. ■ The fork is called once, but returns twice! – After the fork, the original process and the copy (the parent and child) go their separate ways. – The fork call returns a value, which is zero in the child and equal to the child's process identifier or PID in the parent. ■ Now consider how fork is used by the shell. When a command is typed, the shell forks off a new process. This child process must execute the user command. Fork() – PID (Process IDentity) ■ pid < 0 → the creation of a child process was unsuccessful. ■ pid == 0 → the newly created child. ■ pid > 0 → the process ID of the child process passes to the parent. Consider a piece of program: #include <unistd.h> P1 fork() C1 pid_t pid = fork(); PID:28 PID:34 printf(“PID: %d\n”, pid); …. The parent will print: PID: 34 And the child will always print: PID: 0 Fork() #define TRUE 1 while (TRUE) { /* repeat forever */ type_prompt(); /* display prompt on the screen */ read_command(command, parameters); /* read input from terminal */ if (fork() != 0) { /* fork off child process */ /* Parent code.
    [Show full text]
  • Assignment 1
    Assignment 1 Teaching Assistant: Michalis Pachilakis ( [email protected]) System Calls If a process is running a user program in user mode and needs a system service, such as reading data from a file, it has to execute a trap instruction to transfer control the operating system. Application –USER SPACE System call KERNEL SPACE System Calls A system call is a request for service that a program makes of the kernel. The service is generally something that only the kernel has the privilege to do, such as doing I/O. SYSTEM CALLS PROCESS CONTROL fork(), wait(), exec(),exit() FILE open(), close(), MANIPULATION read(), write() DIRECTORIES mkdir(),rmdir(), MANAGEMENT mount(),link() OTHER chdir(),chmod(), kill(),time() Fork() Fork creates a new process(child process). It creates an exact duplicate of the original process, including all the file descriptors, registers etc. The fork is called once, but returns twice! After the fork, the original process and the copy(the parent and the child) go their separate ways. The fork call returns a value, which is zero in the child and equal to the child’s process identifier (PID) in the parent. Now consider how fork is used by the shell. When a command is typed, the shell forks off a new process. This child process must execute the user command. Fork() – PID (Process IDentity) pid < 0 the creation of a child process was unsuccessful. pid == 0 the newly created child. pid > 0 the process ID of the child process passes to the parent Consider the program: #include <unistd.h> P1 fork() C1 PID:28 PID:34 pid_t pid = fork(); printf(“PID:%d\n”,pid); … The parent will print: PID:34 The child will always print: PID:0 Fork() #define TRUE 1 while (TRUE) { /* repeat forever */ type_prompt(); /* display prompt on the screen */ read_command(command, parameters); /* read input from terminal */ if (fork() != 0) { /* fork off child process */ /* Parent code.
    [Show full text]
  • Digital Notes on Linux Programming (R17a0525)
    DIGITAL NOTES ON LINUX PROGRAMMING (R17A0525) B.TECH III YEAR - I SEM (2019-20) DEPARTMENT OF INFORMATION TECHNOLOGY MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) (Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – ‘A’ Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Hakimpet), Secunderabad – 500100, Telangana State, INDIA. Linux Programming Page 1 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY DEPARTMENT OF INFORMATION TECHNOLOGY III Year B.Tech IT – I Sem L T /P/D C 4 - / - / - 4 (R17A0525)LINUX PROGRAMMING Objectives: To develop the skills necessary for Unix systems programming including file system programming, process and signal management, and interprocess communication. To make effective use of Unix utilities and Shell scripting language such as bash. To develop the basic skills required to write network programs using Sockets. UNIT I Linux Utilities-File handling utilities, Security by file permissions, Process utilities, Disk utilities, Networking commands, Filters, Text processing utilities and Backup utilities. Sed-Scripts, Operation, Addresses. Awk- Execution, Fields and Records, Scripts, Operation, Patterns, Actions. Shell programming with Bourne again shell(bash)- Introduction, shell responsibilities, pipes and Redirection, here documents, running a shell script, the shell as a programming language, shell meta characters, file name substitution, shell variables, shell commands, the environment, quoting, test command, control structures, arithmetic in shell, shell script examples. UNIT II Files and Directories- File Concept, File types, File System Structure, file metadata- Inodes, kernel support for files, system calls for file I/O operations- open, create, read, write, close, lseek, dup2,file status information-stat family, file and record locking-lockf and fcntl functions, file permissions - chmod, fchmod, file ownership- chown, lchown, fchown, links-soft links and hard links – symlink, link, unlink.
    [Show full text]
  • Basic Multiprocessing in UNIX
    BasicBasic MultiprocessingMultiprocessing inin UNIXUNIX WithWith ExamplesExamples ParallelParallel ApplicationsApplications ModernModern computerscomputers havehave multiplemultiple CPUCPU corescores (and/or(and/or multiplemultiple CPUs)CPUs) onon boardboard WeWe havehave toto bebe ableable toto utilizeutilize thethe computingcomputing powerpower byby parallelizingparallelizing ourour taskstasks CPUCPU InformationInformation LinuxLinux computer:computer: /proc//proc/cpuinfocpuinfo CatCat /proc//proc/cpuinfocpuinfo example:example: processor : 0 vendor_id : AuthenticAMD cpu family : 15 model : 65 model name : Dual-Core AMD Opteron(tm) Processor 8220 stepping : 3 cpu MHz : 2800.000 cache size : 1024 KB physical id : 0 siblings : 2 core id : 0 cpu cores : 2 fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt rdtscp lm 3dnowext 3dnow pni cx16 lahf _lm cmp_legacy svm extapic cr8_legacy bogomips : 5625.16 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management: ts fid vid ttp tm stc ProcessesProcesses inin UNIXUNIX UNIXUNIX isis nativelynatively parallelparallel operatingoperating systemsystem AA processprocess isis anan instanceinstance ofof runningrunning aa programprogram EachEach processprocess hashas aa uniqueunique processprocess idid ShellShell commandcommand ““psps”” givesgives thethe listlist ofof allall runningrunning
    [Show full text]
  • Lecture 3 : Process Management
    Lecture 3 : Process Management INSTRUCTOR : DR. BIBHAS GHOSHAL ([email protected]) 1 Lecture Outline What is Process? Process States Process Creation Process Address Space Creating a process by Cloning Process Termination Zombie Process Orphans Process Process Address Map in xv6 2 Process Program in Execution Process Comprises of: #include<stdio.h> . Code int main(){ . Data In User space of process Char str[] = “Hello World!\n”; . Stack Printf(“%s”,str); . Heap } . State in OS . $ gcc hello.c Kernel stack In Kernel space of process ELF Process Executable(a.out) $ ./a.out Program Process . Code + static & global data . Dynamic instantiation of code + data + heap + stack + process . One program can create several state processes . A process is unique isolated entity 3 Data Structure of Process Stack Recursive calls Attributes of a Process . Process Id Heap Dynamic allocation of data structures . Program counter . Static Variable Process State . & Once created, it will be there for lifetime Priority . Global Variable General Purpose Register . List of open files Executable a.out . List of open devices . Protection While executing a process, you are restricted to process boundary or else segmentation fault will occur. Heap grows upwards while Stack grows downwards. 4 Process State Process Scheduled Exit NEW READY RUN Terminate ◦ Created I/O Request over I/O Request WAIT Running: In the running state, a process is running on a processor. This means it is executing instructions. Ready: In the ready state, a process is ready to run but for some reason the OS has chosen not to run it at this given moment. Wait: In the blocked state, a process has performed some kind of operation that makes it not ready to run until some other event takes place.
    [Show full text]
  • Introduction To
    UNIVERSITY OF ENGINEERING AND TECHNOLOGY, TAXILA FACULTY OF TELECOMMUNICATION AND INFORMATION ENGINEERING SOFTWARE ENGINEERING DEPARTMENT OPERATING SYSTEM LAB #05 System Calls In UNIX System Call: A system call is just what its name implies—a request for the operating system to do something on behalf of the user’s program. fork() wait() exec() exit() fork() When the fork system call is executed, a new process is created which consists of a copy of the address space of the parent. The return code for fork is zero for the child process and the process identifier of child is returned to the parent process. On success, both processes continue execution at the instruction after the fork call. On failure, -1 is returned to the parent process. fork()—Sample Code Operating System 4th Semester-2k11-SE UET Taxila UNIVERSITY OF ENGINEERING AND TECHNOLOGY, TAXILA FACULTY OF TELECOMMUNICATION AND INFORMATION ENGINEERING SOFTWARE ENGINEERING DEPARTMENT Implementing fork() system call using C program #include<stdio.h> #include <unistd.h> /* contains prototype for fork */ #include <sys/types.h> main() { pid_t pid; pid = fork(); if (pid == 0) printf("\n I'm the child process"); else if (pid > 0) printf("\n I'm the parent process. My child pid is %d", pid); else perror("error in fork"); } /* Note: pid_t is a data type defines in types.h. Q: pid_t is a signed integer type only. Then why should we use pid_t? A: We don't have to know what type of integer (an int, short int, or long int ) the implementation uses for a pid value. So we use pid_t.
    [Show full text]