The sixth week of Linux kernel design learn to summarize and analyze the process of creating a new process for the Linux kernel

Chen Chaojan Original works reproduced please specify the source "Linux kernel Analysis" MOOC course http://mooc.study.163.com/course/USTC-1000029000first, the experimental process

Landing Lab Building Virtual machine http://www.shiyanlou.com/courses/195

Open the shell terminal and execute the following command:

CD Linuxkernel

RM-RF Menu

git clone https://github.com/mengning/menu.git

CD Menu

MV Test_fork.c test.c

Make Rootfs

You can see that the MENUOS has already included the Fork command after the boot.

Debug mode can be opened by adding-s-s startup parameters

Qemu-kernel LINUX-3.18.6/ARCH/X86/BOOT/BZIMAGE-INITRD Rootfs.img-s-S

Open GDB for remote debugging

Gdb

File Linux-3.18.6/vmlinux

Target remote:1234

Set breakpoints

b sys_clone

b do_fork

b dup_task_struct

b copy_process

b copy_thread

b ret_from_fork

second, the experimental analysis

The experiment shows that the fork () function creates a new process that is implemented by the following series of functions:

Copy_thread (), copy_process (), Dup_task_struct (), Do_fork (), Sys_clone (), fork () Ork ()

Iii. Summary of the experiment

The three main management functions of the operating system include: Process management, memory management, file system.

Fork, Vfork, clone three system calls can create a new process, and all by calling Do_fork to achieve;

Linux creates a new process by replicating the parent process;

From the user-state code, the fork () function returned two times, that is, in the parent, child process each return, where the parent process return code is a child process PID, the child process return code is 0.

A negative value is returned when the fork () function call fails, and there are 2 main reasons for the failure:

1, the current number of processes has reached the system specified upper limit, then the value of errno is set to Eagain (one-Try again);

2, the system memory is insufficient, then the value of errno is set to Enomem (out of memory).

About the init process creation:

Daosh a Start_kernel ... cpu_idle

Life two Kernel_init Kthreadd

Secondary 30 1 2

Sansheng 1th process is the ancestor of all user-state processes the 2nd process is the ancestor of all kernel threads

The sixth week of Linux kernel design learn to summarize and analyze the process of creating a new process for the Linux kernel