Table of Contents Overview Linux Kernel Intuition Overview Creating VirtualBox env Kernel Building and Installation Linux Device Drivers Basics How to check devices Scull driver drivers Signals Basics Details Signal masks Linux Signals API sigaction()/signal(): Change signal actions kill(): Send signals Linux Application Level Creating C Library

Overview

http://wiki.osdev.org

Linux Kernel

Intuition

문제:
- 기계가 하나 주어져있다. 프로세서, 메모리, 디스크 시스템이 있다.
- 즉, 이 기계를 쓰는 유일한 방법은 프로그램을 메모리에 올리고 IP를 지정해주는 방법이다. 프로세스의 컨트롤을 위해서는 Bios firmware를 통해 time-0부터 장악을해야 한다. -- 아주 길들이기 힘든 말을 길들인다고 생각하자.
Multiprogramming:
- 프로그램들 여럿이 프로세서 하나를 공유하게 하고 싶다. 이를 위해 bookkeeping이 필요하다. context switch를 위해서 상태를 load/save해야 한다. Load/save는 어디에 하나? 당연히 memory에. 또 현재 살아있는 process들에 대한 정보를 process table에 저장 -- 역시 메모리에.
- 이상의 메모리 사용은 meta-level에서 OS가 사용하는 메모리. 그러나 개별 프로세스들도 자체적으로 메모리를 사용할수 있다. 이를 위해, 특별한 function (malloc/free)를 만든다.
Protection/Service:
- 사실 프로세서 입장에서는 kernel이나 user-space program이나 차이가 없었다. 요즘은 protection을 위한 mechanism을 프로세서에서 제공을하지만 (e.g. flag bit).
- 만약 user-program이 low-level memory (OS-maintained space)에 직접 갈수 있게 한다면 온갖문제가 생긴다. Bad hacker는 말할것도 없고, 선량한 사용자도 system을 얼마든지 망가뜨릴수 있다.
- 따라서 "Service" -- Don't do it yourself -- I'll do it for you.
Devices:
- 독자적으로 동작하는 외부 peripheral들은 어떻게 제어할것인가?
- 표준화된 access(R/W): File + File operations

Overview

i386 programmer's manual: http://pdos.csail.mit.edu/6.828/2014/readings/i386/toc.htm

Creating VirtualBox env

$ sudo usermod -a -G sudo cjeong 
$ <change to bridged networking>
$ sudo vi /etc/network/interfaces
  auto eth1
  iface eth1 inet dhcp
$ sudo service networking restart
$ <REBOOT if failed to access network>

Kernel Building and Installation

Build kernel: https://wiki.ubuntu.com/Kernel/BuildYourOwnKernel, https://help.ubuntu.com/community/Kernel/Compile
- clean: fakeroot debian/rules clean
- build: fakeroot debian/rules binary-headers binary-generic
- install: sudo dpkg -i linux*2.6.38-7.37*.deb
  - in case of failure, do:
    - sudo apt-get -f install
    - sudo apt-get autoremove
      - if not work delete cache file in /var/cache/*******
- reboot: sudo reboot

Linux Device Drivers

Basics

Three module types: char module, block module, network module
FreeBSD: ISA Devide Drivers
- Bus Memory Mapping
- DMA

How to check devices

ls /dev
- do 'ls -l': "c" are char devices, "b" are block devices
cat /proc/devices: shows major device numbers

Scull driver

drivers

scull0-3: global/persistent memory area
scullpipe0-3: FIFO devices
scullsingle, scullpriv, sculluid, scullwid:

Signals

Basics

signal (aka software interrupts): notification to a process that an event has occurred
- it is an interrupt in the sense, it allows to add reactive behavior through signal handler
signal generated by:
- user process to be sent to another
- user process to be sent to itself
- the kernel for a user process
  - hardware exception: e.g. devide-by-zero, segfault
  - Ctrl-C, Ctrl-Z
  - software event: e.g. input became available on a file descriptor
classes of signals:
- traditional/standard signals (numbered 1 ~ 31): used by the kernel to notify processes of events (numbered 1 to 31)
- realtime signals

Details

Signal is generated by some event
Once generated, signal is later delivered to a process, which then takes some action in response to the signal.
Between the time it's generated and the time it's delivered, a signal is said to be pending
Normally, a pending signal is delivered to a process as soon is it next scheduled to run, or immediately if the process is already running

Signal masks

However, we need to ensure that a segment of code is not interrupted by the delivery of signal.
To do this, we can add a signl to the process's signal mask -- a set of signals whose delivery is currently blocked
- blocked signals, when generated, remains pending until it's unblocked (i.e. removed from signal mask) later

Linux Signals

API

sigaction()/signal(): Change signal actions

two ways: signal() and sigaction()
- sigaction can do more than signal and is more portable; more recommended

     #include <signal.h>

     int sigaction(int signum, const struct sigaction *act,
                   struct sigaction *oldact);

     struct sigaction {
       void     (*sa_handler)(int);
       void     (*sa_sigaction)(int, siginfo_t *, void *);
       sigset_t sa_mask;
       int      sa_flags;
       void     (*sa_restorer)(void);
     };

signal delivery:

kill(): Send signals

     #include <signal.h>
     int kill(pid_t pid, int sig);

Linux Kernel - modrpc/info GitHub Wiki

Table of Contents

Overview

Linux Kernel

Intuition

Overview

Creating VirtualBox env

Kernel Building and Installation

Linux Device Drivers

Basics

How to check devices

Scull driver

drivers

Signals

Basics

Details

Signal masks

Linux Signals

API

sigaction()/signal(): Change signal actions

kill(): Send signals

Linux Application Level

Creating C Library

⚠️ GitHub.com Fallback ⚠️

Linux Kernel - modrpc/info GitHub Wiki

Table of Contents

Overview

Linux Kernel

Intuition

Overview

Creating VirtualBox env

Kernel Building and Installation

Linux Device Drivers

Basics

How to check devices

Scull driver

drivers

Signals

Basics

Details

Signal masks

Linux Signals

API

sigaction()/signal(): Change signal actions

kill(): Send signals

Linux Application Level

Creating C Library

⚠️ **GitHub.com Fallback** ⚠️

⚠️ GitHub.com Fallback ⚠️