Linux Kernel Analysis Sixth week analysis of the Linux kernel creating a new process

Description of the process

The three main management functions of the operating system: process management, memory management, file system

To manage the process, the kernel must have a clear description of each process, and the process descriptor provides the process information that the kernel needs to understand.

Process Control block PCB task_struct: Process status, Process-open files, process priority information

Task_struct abstraction of the overall data structure:

tty：控制台fs：文件系统files：文件描述符mm：内存管理signal：信号描述

Status of the process:

Note: Under Linux, both the ready state and the running state are task_running

One, gdb trace analysis a fork system call kernel processing function Sys_clone

Second, reading comprehension TASK_STRUCT data structure

Iii. Creating a new process

Copy a pcb--task_struct

Assigning a new kernel stack to a new process

Modify the copied process data, such as PID, process chain list

Iv. where does the new process begin?

Fork out the child process from the ret_from_fork beginning to execute, and then jump to syscall_exit , return from the system call.

Fork function to create a child process

Fork the code of a child process

#include <stdio.h>#include <stdlib.h>#include <unistd.h>int main(int argc, char * argv[]){int pid;/* fork another process */pid = fork();if (pid < 0) {     /* error occurred */    fprintf(stderr,"Fork Failed!");    exit(-1);} else if (pid == 0)  //子进程pid == 0时返回，子进程是在内核中返回{    /* child process */    printf("This is Child Process!\n");} else //父进程可以返回{      /* parent process  */    printf("This is Parent Process!\n");    /* parent will wait for the child to complete*/    wait(NULL);    printf("Child Complete!\n");}}

Vi. Summary

All process creation in Linux is based on replication, and Linux creates a new process by replicating the parent process, by invoking Do_ Fork, and then modifying the necessary information to get the task_struck of the child process.

The new child process that fork creates is executed from the ret_from_fork start, and then jumps to syscall_exit , returned from the system call.

Linux Kernel Analysis Sixth week analysis of the Linux kernel creating a new process