Week Six: Description of the process and creation of the process

Lu Songhon + Original works reproduced please specify the source + "Linux kernel analysis" MOOC course http://mooc.study.163.com/course/USTC-1000029000

I. Description of the process 1. Three main functions of the operating system:

Process Management memory Management file system

2. Process Descriptor TASK_STRUCT Data structure

struct : In order to manage processes, the kernel must have a clear description of each process, and the process descriptor provides the process information that the kernel needs to understand. Status of the process: the state of the Linux process (ready state, run state, blocked state) the indicator PID of the process: used to mark the process

Status of the 3.Linux process

4. Process descriptor TASK_STRUCT Data structure:

structtask_struct {volatile LongState/*running state of the process -1 unrunnable, 0 runnable, >0 stopped*/void*stack;/*the kernel stack for the process is specified*/atomic_t usage;unsignedintFlags/*identifiers for each process*/intON_RQ;/*Run Queue*/pid_t pid;/*Process Identifiers*/struck List_head task; /*Process Chain List*//*Parent-Child processes*/structTask_struct __rcu *real_parent;/*Real Parent Process*/structTask_struct __rcu *parent;structList_head children;/*List of my children*/

Ii. creation of the process

There are 3 system calls to create a process, they go through the unified system call interface into the kernel mentality to run their own ways, each call their own kernel functions sys_fork, sys_clone, sys_vfork processing. These three functions end up calling the Do_fork function to create a child process, but using different parameters. Linux creates a new process by copying the parent process: Copy the parent process PCB-task_struct to create a new process to assign a new kernel stack to the new process. Modify the copied process data, such as PID, process chain list and so on to perform copy_process and Copy_thread. After that, the new process starts from ret_from_fork. 

#include <stdio.h>#include<stdlib.h>#include<unistd.h>intMainintargcChar*argv[]) {    intpid; /*Fork Another process*/PID=Fork (); if(PID <0)     {         /*error occurred*/fprintf (stderr,"Fork failed!"); Exit (-1); }     Else if(PID = =0)     {        /*Child Process*/printf ("This is the child process!\n"); }     Else     {         /*Parent Process*/printf ("This is the Parent process!\n"); /*parent would wait for the*/Wait (NULL); printf ("Child complete!\n"); }}

Iii. experimental content 1. Delete menu, download new code and execute.

2.GDB Commissioning

3. Set Breakpoints

4. Single-Step tracking

Iv. Summary

Linux creates a new process by copying the parent process: Copy the parent process pcb--task_struct to create a new process and assign a new kernel stack to the new process. Modify the copied process data, such as PID, process chain list and so on to perform copy_process and Copy_thread. Set the SP Scheduler to the child process when the kernel stack top, IP to the child process when the first instruction address, when the child process to gain control of the CPU to start running, ret _ form _ fork can be back stack out of the stack, from Iret back to the user state, thereby switching to the child process user space, Complete the creation of the new process. 

Week Six: Description of the process and creation of the process