Introduction on FreeBSD Operating System

1
Introduction on FreeBSD Operating System
2
Agenda

• History and Goals
• Kernel Services
• Process Management
• Memory Management
• I/O System
• Interprocess Communication
• System Operation
• Acknowledgments

3
History and Goals

• History of the UNIX System
• BSD and Other Systems
• The Transition of BSD to Open Source
• The FreeBSD Development Model

4
History of the UNIX System

• Bell Lab invented UNIX in 1969
• It was written by C-language
• It was distributed by source form
• It can run cheap hardware with advance features
• CSRG at Berkeley invented BSD in 1979
• Virtual memory, demand paging, page replacement
• Socket interface for TCP/IP
• Job control, reliable signals, filesystem
  interface

5
BSD and Other Systems

• Most features from UNIX
• Terminal drivers from TENEX/TOPS-20
• Job control from TOPS and MITs ITS
• Memory management from Mach
• The Influence of the User Community
• Some packages from other groups
• comp.bugs.4bsd

6
The Transition of BSD to Open Source

• The FreeBSD group was formed in 1993
• Supporting the PC architecture only
• Ease of installation
• Code started base with 4.4BSD-Lite
• Current version is FreeBSD5.4
• Alpha, Space64, X86
• JUNOS is based on FreeBSD4.10

7
The FreeBSD Development Model

• Publicly readable source-code control system
• www.freebsd.org
• Developers groups
• 3000 to 4000 developers
• They are not permitted to change code
• Committees
• 300 to 400 committees
• They are permitted to change code
• Core team can do everything

8
Kernel Services

• FreeBSD Facilities and the Kernel
• System Calls
• Traps and Interrupts
• Clock Interrupts
• Memory Management Services
• Timing Services
• User, Group and Other Identifiers
• Resource Services
• System Operation Services

9
FreeBSD Facilities and the Kernel

• Kernel Provide 4 basic facilities process,
  filesystem, communication, system startup
• Kernel has been organized to the follow
• Basic kernel facilities timer, system-clock
  handling, descriptor management, process
  management
• Memory management paging and swapping
• Generic system interface the I/O, control, I/O
  descriptors
• The filesystem files, directories, pathname
  translation, i/O buffer management
• Interprocess-communication sockets

10
FreeBSD Facilities and the Kernel

• Low-level system-startup actions
• Trap and fault handling
• Low-level manipulation of the run-time context of
  a process
• Configuration and initialization of hardware
  devices
• Run-time support for I/O devices

11
System Calls

• System calls provide a layer between the hardware
  and user-space processes
• Provides an abstracted hardware interface for
  user-space
• Ensure system security and stability
• A single common layer between user-space and the
  rest of the system allows the multi-processes
• Syscall handling
• Verify the parameter to the system call
• Call a kernel routine that implements the system
  call
• Result handling errno

12
Traps and Interrupts

• Traps occur synchronously for process
• Divide by zero, illegal instruction, page fault
• I/O device Interrupts occur asynchronously
• Clocks, Console, Ethernet
• Software Interrupts is doing lower-priority
  processing for I/O interrupts

13
Clock Interrupts

• The system is driven by a clock that interrupts
  at regular intervals which we call tick.
• Most system tick for FreeBSD is 10ms.
• hardclock()
• Increment the current time of day
• Call softclock() if necessary
• softclock()
• Process real-time timer
• Retransmission of dropped network packets
• Watchdog timers on peripherals that require
  monitoring
• System process-rescheduling event

14
Memory Management Services

• Demand paging
• Copy-on-write
• mmap() interface for share memory
• sbrk() for heap allocate

15
Timing Services

• System Real Time
• Interval Time for each process
• Wakeup timer
• Profiling timer kernel and user mode
• Virtual timer user mode

16
User, Group and Other Identifiers

• User identifier (UID) and Group identifier (GID)
• set-user-identifier and set-group-identifier,
  effective uid and effective gid
• Process Groups and Sessions
• Each process in the system is associated with a
  process group
• The group of processes is referred to as a job
• A session is a collection of process groups

17
Resource Services

• Process Priorities nice value
• Resource Utilization
• The amount of user and system time used by
  process
• The memory utilization of process
• The paging and disk I/O activity of process
• The number of voluntary and involuntary context
  switches
• Resource Limits
• Filesystem Quotas

18
System Operation Services

• Accounting
• The name of the command that ran
• The amount of user and system CPU time that was
  used
• The average amount of memory used
• Bootstrapping
• Shutdown
• Debugging

19
Process Management

• Introduction to Process Management
• Process State
• Context Switching
• Process Scheduling
• Process Creation and Termination
• Process Debugging

20
Introduction to Process Management

• The definition of Process
• Design goal for FreeBSD Process management
• Multiprogramming
• Fair Scheduling
• Communication
• Easy management and debugging

21
Process State

• The proc structure
• Process identification PID and PPID
• Scheduling The process priority, user-mode
  scheduling priority, recent CPU utilization, and
  amount of time spent sleeping
• Process state SIDL,SRUN,SSLEEP,SSTOP,SZOMB
• Signal state Signals pending delivery
• Tracing
• Machine state
• Timers

22
Context Switching

• Cause of context switching
• A process executes for the duration of its time
  slice
• A process block for resource
• The system interrupts the current process
• Voluntary Context Switching
• sleep() and wakeup()
• Synchronization
• Set-priority-level, spl0, splsoftclock, splnet,
  , splhigh

23
Process Scheduling

• I/O-Bound Versus Processor-Bound
• FreeBSD favors I/O bound
• Multilevel feedback queue
• Round robin for same queue
• Calculations of Process Priority
• p_estcpu an estimate of the recent CPU
  utilization of this process
• p_nice user-settable weighting factor that
  ranges from -20 to 20

24
Process Creation and Termination

• Parent process and child process
• fork(), vfork() and rfork()
• Implementation of fork1()
• Termination exit() OR signal
• wait4() and SZOMB

25
Process Debugging

• ptrace system call
• Read and write address space and registers
• Intercept signals posted to the process
• Single step and continue the execution of process
• Terminate the execution of the process
• Inefficient of ptrace
• /proc file system

26
Memory Management

• Overview of the FreeBSD VM System
• Kernel Memory Management
• Per-Process Resources
• Shared Memory
• Process Related Memory Operation
• The Pager interface
• Placement and Replacement

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Overview of the FreeBSD VM System

• FreeBSD VM is paging system
• Three important policies
• The fetch policy
• The placement policy
• The replacement policy
• Swapping
• mmap system call for shared memory

28
Kernel Memory Management

• Kernel is permanently mapped into up 1G of every
  process address space
• Kernel Maps and Submaps
• kmem_alloc(), kmem_alloc_pageable(), kmem_free()
• Kernel malloc
• Kernel Zone Allocator

29
Per-Process Resources
Vm_map_entry
Vnode/object
vmspace
vm_page
Start addr End addr Obj offset
Vm_map
vm_page
Vm_pmap
Vnode/object
vm_page
Start addr End addr Obj offset
statistics
vm_page
Vnode/object
vm_page
Start addr End addr Obj offset
vm_page
30
Shared Memory

• mmap(caddr_t address, size_t length, int
  protection, int flags, int fd, off_t offset)
• munmap
• mprotect
• mlock and munlock
• msync

31
Process Related Memory Operation

• Create of a New Process
• copy-on-write
• Load a execute file
• page-on-demand
• Process manipulation of its address space
• sbrk, mmap, mprotect
• Termination of Process

32
The Pager interface

• Vnode Pager
• Handles objects that map files in a filesystem
• Device Pager
• Handles objects representing memory-mapped
  hardware devices
• Physical-Memory Pager
• Handles nonpagable memory for System V shm
• Swap Pager
• Handles object that map anonymous memory
• Handles shadow object

33
Placement and Replacement

• Page Coloring
• L1 Cache Coloring
• L2 Cache Coloring
• Page Replacement
• Global least-recently used page
• Wired, active, inactive, cache, free
• Swapping

34
I/O System

• I/O System Overview
• Devices
• The Filesystems

35
I/O System Overview

• Four main kinds of I/Os filesystem,
  character-device, block-device, socket interface
• Devices identified by a major and minor number
• The Virtual-Filesystem Interface
• Descriptor Management Services
• Filesystem-Independent Services
• Name cache, Buffer management
• Stackable Filesystems

36
Devices

• Device Naming and Access
• Static device node under /dev
• DEVFS for dynamical device management
• Asynchronous I/O
• aio_read, aio_write
• Mutliplexing I/O on Descriptors
• select()

37
The Filesystems

• Virtual-Filesystem Interface
• vnode operation
• Pathname translation
• Exported Filesystem Services
• Name cache and Buffer Management
• Physical-Filesystem interface
• Structure of inode
• Implementation of Filesystem Services

38
Interprocess Communication

• SYSV Interprocess communication
• POSIX 1003.1b is not implemented in kernel
• Socket API
• Network Communication
• Network Protocols

39
SYSV Interprocess communication

• sysv ipc
• ftok
• sysv message queue
• msgget, msgsnd, msgrcv, msgctl
• sysv semaphore
• semget, semop, semctl
• sysv shared memory
• shmget, shmat, shmdt, shmctl, shmids

40
System Operation

• Bootstrapping
• Kernel Initialization
• Kernel Module Initialization
• User-Level Initialization
• System Shutdown and Autoreboot
• Configuration, Build and Debugging

41
Bootstrapping

• BIOS loads boot
• Commands for boot
• boot, autoboot, help, load
• Boot loads FreeBSD kernel from BSD filesystem
• Boot passes the information to kernel
• Boot need disable mmu and interrupts

42
Kernel Initialization

• Setting up the run-time stack
• Identifying the type of CPU
• Calculating the amount of physical memory
• Initializing MMU hardware and Enable the MMU
• Crafting the hardware context for process 0
• Invoking the initial C-base entry point

43
Kernel Module Initialization

• Entry point mi_startup()
• SYSINIT(name, subsystem,order, function,)
• Basic services
• Kernel Thread Initialization
• Device Module Initialization
• Kernel Loadable Modules
• Interprocess Communication Startup
• Start Kernel Threads

44
User-Level Initialization

• /sbin/init
• Check consistency of its disk by fsck
• Single-user mode /bin/sh and /dev/console
• Multi-user mode /etc/rc and /etc/ttys

45
System Shutdown and Autoreboot

• reboot system call
• panic() causes system reboot
• Three phases for shutdown
• Shutdown of all services rely to the filesystem
• Shutdown of the filesystem itself
• Shutdown other services

46
Configuration, Build and Debugging

• make buildkernel KERNCONFltcfgfilegt
• make installkernel KERNCONFltcfgfilegt
• Crash dump file /sbin/savecore
• Using /dev/kmem to talk to kernel

47
Acknowledgements

• http//www.freebsd.org
• The Design and Implementation of FreeBSD