os-team20

How to Build

Building the kernel is simple. Just type

$ build

on the top directory of this repo.

To build the test code, type

$ sh test/build.sh test1.c

on the top directory. The executable will be located in "test" directory.

High-Level Design & Implementation

System call ptree[sys_ptree(380)] is implemented using recursive strategy. The algorithm consists of three parts.

1. Start with init_task, which is the initial task with pid 0.
2. Given a task, push it into the buffer
3. Repeat 2 and 3 for every child process and halt.

Overall design is depicted in the diagram below.

To avoid using global variable and achieve better design, we used our own structure named SearchResult to manage prinfo values. It's a basic implementation of array list.

struct SearchResult {
	struct prinfo *data; // pointer to prinfo array
	int max_size;        // length of <data>
	int count;           // actual number of prinfo elements
};

Lessons Learned

• 프로젝트는 역시 일찍 하는 것이 좋다.
• 커널패닉은 고통스럽지만 printk()와 함께라면 두렵지 않다.
• 손가락부터 움직여선 안되고 반드시 먼저 생각하고 코딩해야 한다.

자주 쓰는 커맨드

SDB 사용하는 법

먼저 정상적으로 artik 부팅하고 root로 로그인, 다음 커맨드를 입력.

direct_set_debug.sh --sdb-set

우분투 환경에서 sdb root로 전환 후 push

sdb root on
push [원본파일] [destination]

printk 출력 레벨 변경

echo 8 > /proc/sys/kernel/printk

이렇게 하면 모든 메시지가 콘솔에 출력됨

How To Register System Call

1. Increment the number of System calls

in file: "arch/arm/include/asm/unistd.h"

#define __NR_syscalls  (N)

to

#define __NR_syscalls  (N+4)

Total number of system calls must be a multiplication of 4.

2. assign system call number

in file: "arch/arm/include/uapi/asm/unistd.h" add

#define __NR_myfunc      (__NR_SYSCALL_BASE+ #) 

3. make asmlinkage function

in file: "include/linux/syscalls.h"

asmlinkage int my_func()  // if no parameter then write 'void' 

4. add to system call table

in file: "arch/arm/kernel/calls.S"

call(sys_myfunc)

5. Revise Makefile

in file: "kernel/Makefile"

obj -y = ...  ptree.o

etc.

in file: "kernel/myfunc.c"
the name of function must be sys_myfunc()