OS/Kernel Structure

1
OS/Kernel Structure

• Module 01

2
MS-DOS Layer Structure
3
Unix is a monolithic system

• UNIX the original UNIX operating system had
  limited structuring. The UNIX OS consists of two
  separable parts.
• Systems programs
• The kernel
• Consists of everything below the system-call
  interface and above the physical hardware
• Provides the file system, CPU scheduling, memory
  management, and other operating-system functions
  a large number of functions for one level.

4
UNIX System Structure
5
System Structure Layered Approach

• The operating system is divided into a number of
  layers (levels), each built on top of lower
  layers. The bottom layer (layer 0), is the
  hardware the highest (layer N) is the user
  interface.
• With modularity, layers are selected such that
  each uses functions (operations) and services of
  only lower-level layers.
• Why layering?
• explicit structure allows identification,
  relationship of complex systems pieces
• modularization eases maintenance, develop,
  updating of system
• change of implementation of layers service
  transparent to rest of system
• e.g., change in gate procedure doesnt affect
  rest of system
• layering considered harmful?

6
Layered Structure of the THE OS

• A layered design was first used in THE operating
  system.
• Its six layers are as follows

layer 5 user programs
layer 4 buffering for input and output
layer 3 Process management
layer 2 memory management
layer 1 CPU scheduling
layer 0 hardware
7
OS/2 Layer Structure
8
Microkernels

• Small operating system core
• Contains only essential operating systems
  functions
• Many services traditionally included in the
  operating system are now external subsystems
• device drivers
• file systems
• virtual memory manager
• windowing system
• security services

9
(No Transcript)
10
Benefits of a Microkernel Organization

• Uniform interface on request made by a process
• All services are provided by means of message
  passing, not system calls.
• Examples of opening a file
• Creating threads
• Extensibility
• Allows the addition of new services
• Flexibility
• New features added
• Existing features can be subtracted

11
Benefits of a Microkernel Organization

• Portability
• Changes needed to port the system to a new
  processor is changed in the microkernel - not in
  the other services
• Reliability
• Modular design
• Small microkernel can be rigorously tested

12
Benefits of Microkernel Organization

• Distributed system support
• Message are sent without knowing what the target
  machine is
• Object-oriented operating system
• Components are objects with clearly defined
  interfaces that can be interconnected to form
  software

13
Microkernel Design

• Microkernel must include functions that depend on
  the HW and functions needed to support the
  servers and applications operating in user mode.
• Low-level memory management
• mapping each virtual page to a physical page
  frame. Other memory functions like swapping,
  protection, paging, etc is done by VM service.
• Inter-process communication
• Using ports. A port is a mailbox associated with
  one receiver and multiple senders.
• I/O and interrupt management
• Interrupts are transformed into messages.

14
KLM

• Examples of ukernels are Mach and Chorus
• Are the basis for KLM (Kernel Loadable Modules)
• Linux modules are located in /lib/modules and
  they have had the extension ".ko" since version
  2.6.
• Sound
• Device Drivers
• Network support (Apple Talk, Novel, etc)
• Language support
• VM (the virtualization layer)
• etc

15
Virtual Machines

• A virtual machine provides multiprogramming only
  by providing exact virtual copies of the bare
  hardware .
• A virtual machine provides an interface identical
  to the underlying bare hardware.
• The operating system creates the illusion of
  multiple processes, each executing on its own
  processor with its own (virtual) memory.
• Virtual Machine A machine implemented in
  software, not actual hardware. Also known as a
  machine emulator, not as OS simulator.
• Each virtual machine can run any OS on top of it
• You can run different OSs, each best suited for
  some task, on the same physical machine
• Similar to Java approach. JVM is an application
  VM.
• Virtual PC for Windows allows you to create
  separate virtual machines on top of your
  Windows desktop, where you can install virtually
  any PC-based operating system including OS/2,
  Linux, Solaris, NetWare or other versions of
  Windows. Each virtual machine emulates a complete
  hardware system from processor to network card
  in a self-contained, isolated software
  environment, enabling the simultaneous operation
  of otherwise incompatible systems.

16
Virtual Machines (Cont.)

• The resources of the physical computer are shared
  to create the virtual machines.
• CPU scheduling can create the appearance that
  users have their own processor.
• Spooling and a file system can provide virtual
  card readers and virtual line printers.
• A normal user time-sharing terminal serves as the
  virtual machine operators console.
• Instruction set emulation
• Benefits of VM OS
• A big plus for SW development can run and test
  SW simultaneously on multiple OS on a single
  machine, without rebooting. Testing can take
  place with different system configuration, like
  memory, disk space, etc.
• IT professionals can safely migrate and deploy
  new operating systems while continuing to run
  and support older or custom legacy applications.
• Internet VPS
• Cloud Computing Amazon Elastic CC (or EC2)
• Testing networked machines with multiple NEs
  (routers, FWs, etc)
• Testing and parallel and distributed programming
  for cluster nodes
• Sandboxing play and test in a protected
  environment w/o risking damage to other kernels
  running.
• Server consolidation virtualization allowed a
  single server to replace multiple underutilized
  dedicated servers.
• Any drawbacks?

17
System Models
Similar to standalone Hyber-V whereby a thin
layer is installed first
Virtual Machine (Classical Type originated by
IBM VM370 in 1972)
Non-virtual Machine
Virtualization layer or Hypervisor or VMM
Possible that it can span over multiple CPUs
(even in a distributed fashion). Referred as
Platform Virtualization

• VmWare (from Vmware Inc.),
• Virtual PC (Connectix, now Mircorsoft, Integrated
  within Windows 7 to run all Windows XP apps)
• KVM (preferred choice for Red Hat and Ubuntu)
• Xen (freeware)
• Virtualbox from Sun Inc.
• A complete list is available at
  http//en.wikipedia.org/wiki/Comparison_of_platfor
  m_virtual_machines

18
VMware architecture Common Type (e.g. vmware)
19
Modern Virtualization

• Intel VT and AMD-V processors have hardware
  assisted virtualization to yield better
  performance
• Full vs. Partial Virtualization
• Much of the underlying hardware is emulated, but
  not all
• Paravirtualization
• Guest OS has special calls to VM, called
  hybervisor calls to speed access
• i.e. it provides an interface to VM
• Faster as the virtualization layer becomes
  smaller

20
Windows Hyper-V (2008 Server)
21
Hyper-V Architecture (1/2)

•  A partition is a logical unit of isolation in
  which an OS executes.
• The virtualization stack runs in the parent
  partition and has direct access to the hardware
  devices.
• The parent partition then creates the child
  partitions which host the guest OSs. A parent
  partition creates child partitions using
  the hypercall API.
• A virtualized partition does not have access to
  the physical processor, nor does it handle its
  real interrupts. Instead, it has a virtual view
  of the processor and runs in Guest Virtual
  Address.

22
Hyper-V Architecture (2/2)

• The hypervisor handles the interrupts to the
  processor, and redirects them to the respective
  partition using a logical Synthetic Interrupt
  Controller (SynIC). Hyper-V can hardware
  accelerate the address translation between
  various Guest Virtual Address-spaces by using
  an IOMMU (I/O Memory Management Unit) which
  operates independent of the memory management
  hardware used by the CPU.
• Parent partitions run a Virtualization Service
  Provider (VSP), which connects to the VMBus and
  handles device access requests from child
  partitions. Child partition virtual devices
  internally run a Virtualization Service
  Client (VSC), which redirect the request to VSPs
  in the parent partition via the VMBus.

23
Microsoft Windows

• Single-user multitasking
• From Windows 2000 on, Windows development
  developed to exploit modern 32-bit and 64-bit
  microprocessors
• Designed for single users who run multiple
  programs
• Main drivers are
• Increased memory and speed of microprocessors
• Support for virtual memory

24
Windows Architecture
25
Client/Server Model

• Windows OS, protected subsystem, and applications
  all use a client/server model
• Common in distributed systems, but can be used
  internal to a single system
• Processes communicate via RPC

26
Windows Objects

• Windows draws heavily on the concepts of
  object-oriented design.
• Key Object Oriented concepts used by Windows are
• Encapsulation
• Object class and instance

27
Traditional UNIX Kernel
28
System V Release 4 (SVR4)
29
Linux

• Modular Monolithic Kernel
• Although monolithic, the kernel is structures as
  a collection of modules
• Loadable modules
• An object file which can be linked and unlinked
  at run time
• Characteristics
• Dynamic Linking
• Stackable modules
• For checking dependencies when unloading

30
Example of loading two modules FAT VFAT
VFAT is a client of FAT
31

• next Pointer to the following module. All
  modules are organized into a single linked list.
• name Pointer to module name.
• sizeModule size in memory pages.
• usecountModule usage counter.
• The counter is incremented when an operation
  involving the modules functions is started and
  decremented when the operation terminates.
• flagsModule flags.
• nsyms Number of exported symbols.
• ndeps Number of referenced modules
• syms Pointer to this modules symbol table.
• deps Pointer to list of modules the are
  referenced by this module.
• refs Pointer to list of modules that use this
  module.

32
(No Transcript)
33
(No Transcript)
34
Linux Kernel Components