Transcript Ch1 Introduction to the Linux Kernel

作業系統
Operating Systems
課本：Linux Kernel Development, 3rd Ed., by R. Love, Sams
Publishing. (全華圖書代理)
上課時間：星期二下午5 (204),星期三下午5, 6 (204)
評量方式 ：實習 20% 作業 20% 期中考 30% 期末考 30%
課程網頁：http://ares.ee.nchu.edu.tw/Course.files/os103/
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Kernel Introduction
Process Management
System Calls
Interrupt Handlers
Timers
Memory Management
Virtual Filesystems
I/O Layers
The Process Address Space
Ch1. Introduction to the
Linux Kernel
Introduction to Linux (1)
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Linux was developed by Linus Torvalds in 1991 as
an operating system for computers using the Intel
80386 microprocessor
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Linux is a full-fledged operating system running on
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At the time was a new and advanced processor
AMD x86-64, ARM, Compaq Alpha, CRIS, DEC VAX,
H8/300, Hitachi SuperH, HP PA-RISC, IBM S/390, Intel
IA-64, MIPS, Motorola 68000, PowerPC, SPARC,
UltraSPARC, and v850
It runs on systems as small as a watch to machines
as large as room-filling super-computer clusters.
Introduction to Linux (2)
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Linux is a Unix clone
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Linux borrows many ideas from Unix and
implements the Unix API
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It is not a direct descendant of the Unix source code like
other Unix systems
The basics of a Linux system are
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It is not Unix
The kernel, C library, compiler, tool chain, and basic
system utilities, such as a login process and shell
A Linux system can also include a modern X
Window System implementation
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Including a full-featured desktop environment, such as
GNOME
Overview of Operating
Systems and Kernels (1)
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Many users consider whatever they see on the
screen to be the operating system.
Technically speaking, the operating system is
considered the parts of the system responsible for
basic use and administration
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Includes the kernel and device drivers, boot loader,
command shell or other user interface, and basic file and
system utilities
The term system refers to the operating system and
all the applications running on top of it
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The user interface is the outermost portion of the
operating system
The kernel is the innermost
Overview of Operating
Systems and Kernels (2)
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The kernel is the core internals
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The software that provides basic services for all other
parts of the system, manages hardware, and distributes
system resources
Sometimes referred to as the supervisor, core, or internals
of the operating system.
Typical components of a kernel are:
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Interrupt handlers to service interrupt requests
A scheduler to share processor time among multiple
processes
A memory management system to manage process
address spaces
System services such as networking and interprocess
communication
Overview of Operating
Systems and Kernels (3)
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On modern systems with protected memory
management units
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The kernel typically resides in an elevated system state
compared to normal user applications
This includes a protected memory space and full access to
the hardware
This system state and memory space is collectively
referred to as kernel-space
User applications execute in user-space
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See a subset of the machine's available resources
Unable to perform certain system functions, directly
access hardware, or otherwise misbehave
Overview of Operating
Systems and Kernels (4)
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When executing the kernel, the system is in kernelspace executing in kernel mode
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Applications running on the system communicate
with the kernel via system calls
An application typically calls functions in a library,
e.g. the C library
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As opposed to normal user execution in user-space
executing in user mode
In turn rely on the system call interface to instruct the
kernel to carry out tasks on their behalf
Some library calls have a one-to-one relationship
with the kernel
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The open() library function does nothing except call the open()
system call
Overview of Operating
Systems and Kernels (5)
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Still other C library functions make no use of the
kernel at all
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When an application executes a system call, the
kernel is executing on behalf of the application
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The application executes a system call in kernel-space
The kernel is running in process context
This relationship that applications call into the
kernel via the system call interface is
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Such as strcpy()
The fundamental manner in which applications get work
done
The kernel also manages the system's hardware
Overview of Operating
Systems and Kernels (6)
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All systems that Linux supports, provide the
concept of interrupts
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Interrupts are identified by a number
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The kernel uses the number to execute a specific interrupt
handler to process and respond to the interrupt
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As you type, the keyboard controller issues an interrupt to let the
system know that there is new data in the keyboard buffer
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The kernel notes the interrupt number being issued and
executes the correct interrupt handler
The interrupt handler processes the keyboard data and
lets the keyboard controller know it is ready for more data
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When hardware wants to communicate with the system, it
issues an interrupt asynchronously interrupting the kernel
The kernel can usually disable interrupts
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To provide synchronization
Overview of Operating
Systems and Kernels (7)
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In Linux, the interrupt handlers do not run in a
process context
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Either all interrupts or just one specific interrupt number
They run in a special interrupt context that is not
associated with any process
This special context exists solely to let an interrupt handler
quickly respond to an interrupt, and then exit
In Linux, each processor is doing one of three
things at any given moment:
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In kernel-space, in process context, executing on behalf of
a specific process
In kernel-space, in interrupt context, not associated with a
process, handling an interrupt
In user-space, executing user code in a process
Linux Versus Classic Unix
Kernels (1)
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Owing to their common ancestry and same API,
modern Unix kernels share various design traits
With few exceptions, a Unix kernel is typically a
monolithic static binary
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Unix systems typically require a system with a
paged memory-management unit
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It exists as a large single-executable image that runs in a
single address space
Enables the system to enforce memory protection
Provides a unique virtual address space to each process
Characteristics that differ between the Linux kernel
and other Unix variants
Linux supports the dynamic loading of kernel
modules
Linux Versus Classic Unix
Kernels (2)
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Linux has symmetrical multiprocessor (SMP)
support
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Although many commercial variants of Unix now support
SMP, most traditional Unix implementations did not
The Linux kernel is preemptive
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Although the Linux kernel is monolithic, it is capable of
dynamically loading and unloading kernel code on
demand
Unlike traditional Unix variants, the Linux kernel is capable
of preempting a task even if it is running in the kernel
Linux takes an interesting approach to thread
support
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It does not differentiate between threads and normal
processes
Linux Versus Classic Unix
Kernels (3)
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To the kernel, all processes are the same some just
happen to share resources
Linux is free in every sense of the word
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Modifications must solve a specific real-world problem
Have a sane design
Have a clean implementation
Linux Kernel Versions (1)
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Linux kernels come in two flavors
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Stable or development
Stable kernels are production-level releases suitable for
widespread deployment
Linux kernels distinguish between stable and
development kernels with a simple naming scheme
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The first value is the major release
The second is the minor release
The third is the revision
An optional fourth value is the stable version
For the minor release, an even number is stable
An odd number is development
Linux Kernel Versions (2)