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Introduction on FreeBSD Operating System

Introduction on FreeBSD Operating System . Agenda. History and Goals Kernel Services Process Management Memory Management I/O System Interprocess Communication System Operation Acknowledgments. History and Goals. History of the UNIX System BSD and Other Systems

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Introduction on FreeBSD Operating System

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  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 MIT’s 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

  27. 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 vmspace Vnode/object 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 KERNCONF=<cfgfile> • make installkernel KERNCONF=<cfgfile> • Crash dump file /sbin/savecore • Using /dev/kmem to talk to kernel

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

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