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LINUX KERNEL IMAGE

Outline (1/2). Kernel IntroductionOverviewBasic FacilitiesProcess ManagementMemory ManagementDevice ManagementSystem CallsKernel Design DecisionsProtectionProcess CooperationI/O Device ManagementKernel-Wide Design ApproachesMonolithic KernelsMicrokernelsMonolithic Kernels Versus Microk

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LINUX KERNEL IMAGE

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    1. LINUX KERNEL IMAGE LAB 7

    2. Outline (1/2) Kernel Introduction Overview Basic Facilities Process Management Memory Management Device Management System Calls Kernel Design Decisions Protection Process Cooperation I/O Device Management Kernel-Wide Design Approaches Monolithic Kernels Microkernels Monolithic Kernels Versus Microkernels Performances Hybrid Kernels Nanokernels Exokernels

    3. Outline (2/2) Linux vs. Other Unix-Like Kernels Differences from User Application Kernel Configuration Lab Make kernel image and download it to the target machine Homework Reference

    4. Kernel Introduction Overview Manage the system's resources Hardware abstractions Communication between H/W and S/W The necessity for good performance

    5. Kernel Introduction Basic Facilities (1/5) Process Management To run an application Set up address space Load the code into memory Set up a stack Branch to the location inside the program Multi-tasking Pre-emptive multitasking Scheduling algorithms Inter-process communication (IPC) Shared memory Message passing Remote procedure calls (RPC) Multiprocessing SMP Non-Uniform Memory Access (NUMA) Must be designed to be re-entrant

    6. Kernel Introduction Basic Facilities (2/5) Memory Management (1/2) Virtual addressing Paging Segmentation Allow programs to use more memory than the system has physically available Virtual address spaces may be different for different processes Every program to behave as if it is the only one Virtual partitions of memory ? Protection

    7. Kernel Introduction Basic Facilities (3/5) Memory Management (2/2) Demand paging Advantages Not load the pages that are never accessed ? the degree of multiprogramming? Less loading latency at the program startup Less disk overhead Pages will be shared by multiple programs ? BY: Copy-On-Write Ability to run large programs Better than overlay method Does not need extra hardware support Disadvantages Extra latency Replacement algorithms ?more complex Possible security risks, ex: timing attack

    8. Kernel Introduction Basic Facilities (4/5) Device Management Very OS-specific topic Device drivers Maintain a list of available devices Plug and play

    9. Kernel Introduction Basic Facilities (5/5) System Calls Most provide a C library or an API Methods A software-simulated interrupt A call gate A special address Without causing an access violation A special system call instruction Memory-based queue Not need to wait for the result kernel periodically scans to find requests

    10. Kernel Introduction Kernel Design Decisions (1/6) Protection (1/5) Criteria Static or dynamic (compile-time or runtime) Preemptive or post-detection Hardware supported or language based More an open mechanism or a binding policy

    11. Kernel Introduction Kernel Design Decisions (2/6) Protection (2/5) Fault tolerance Hierarchical protection domains (ring architectures) Hardware approach Less flexible Impossible to assign different privileges to the-same-privileged-level processes Impossible to satisfy Denning's 4 principles: Isolation Resource control Decision verification Error recovery

    12. Kernel Introduction Kernel Design Decisions (3/6) Protection (3/5) Fault tolerance Hierarchical protection domains (ring architectures) Always requires message copying (transmission by value) for a data structure both in 'user mode' and 'supervisor mode'. Hardware requirement CPU modes MMU check access-rights for every memory access

    13. Kernel Introduction Kernel Design Decisions (4/6) Protection (4/5) Fault tolerance Capability-based addressing Hardware approach Satisfy Denning's fault tolerance principles

    14. Kernel Introduction Kernel Design Decisions (5/6) Protection (5/5) Security Security policy for malicious behavior on top of firmware and kernel features Delegate some responsibility to the compiler (language-based security) Any security policy can be implemented in an application regardless of kernel support

    15. Kernel Introduction Kernel Design Decisions (6/6) Process Cooperation Atomic lock and unlock operations operating on binary semaphores Message passing Inter-Process Communication (IPC) I/O Device Management

    16. Kernel Introduction Kernel-Wide Design Approaches (1/8) The principle of separation of mechanism and policy A mechanism The support that allows to implement many different policies A policy A particular "mode of operation"

    17. Kernel Introduction Kernel-Wide Design Approaches (2/8) Monolithic Kernels Execute all of their code in the same address space (kernel space) Rich and powerful hardware access

    18. Kernel Introduction Kernel-Wide Design Approaches (3/8) Microkernels Run most of their services in user space ?improve maintainability and modularity A simple abstraction over the hardware A set of primitives or system calls Memory management Multitasking IPC Disadvantages #(system calls) ? #(context switches) ?

    19. Kernel Introduction Kernel-Wide Design Approaches (4/8) Monolithic Kernels Versus Microkernels Problem: memory footprint ? Virtual Memory Linux use a monolithic kernel Tanenbaum-Torvalds debate Tanenbaum, A. S. (May 2006). "Can We Make Operating Systems Reliable and Secure?". IEEE Computer Society 39(5): 4451. Retrieved on 2006-11-26 Torvalds, L. (May 2006). Hybrid kernel, not NT. Real World Technologies. Retrieved on November 30, 2006. Jonathan Shapiro (2006). Debunking Linus's Latest. coyotos.org. Retrieved on May 14, 2007.

    20. Kernel Introduction Kernel-Wide Design Approaches (5/8) Monolithic Kernels Versus Microkernels Most of the field-proven reliable and secure computer systems use a more microkernel-like approach Microkernels are often used in embedded robotic or medical computers where crash tolerance is important Performances Monolithic model is more efficient IPC by: Shared kernel memory instead of message passing (Microkernel) Careful tuning could reduce this overhead in microkernel dramatically ?

    21. Kernel Introduction Kernel-Wide Design Approaches (6/8) Hybrid Kernels monolithic kernel Speed Simpler design microkernel Modularity Execution safety Some services in kernel space, EX: Network stack Filesystem kernel code as servers in user space, EX: Device drivers

    22. Kernel Introduction Kernel-Wide Design Approaches (7/8) Nanokernels Delegate all services to device drivers Kernel memory requirement is smaller than a traditional microkernel

    23. Kernel Introduction Kernel-Wide Design Approaches (8/8) Exokernels MIT Parallel and Distributed Operating Systems group Force as few abstractions as possible on developers Functionality is limited Protection of resources Multiplexing of resources EX: Cheetah web server Xen hypervisor

    24. Linux vs. Other Unix-Like Kernels Dynamic loading of kernel modules Symmetrical multiprocessor Preemptive Do not separate thread and process Thread = Light-Weight Process (LWP) Fully customizable components Very small and compact Low-end, cheap hardware platforms

    25. Differences from User Application No standard C library in kernel GNU C and ISO C99 Inline function Inline assembly No memory protection mechanism Destroying memory data occurs oops Kernel memory could not be paged Small and static stack Only 8KB on 32 bit architecture Floating point numbers Access the floating point registers Handle your operation by hand

    26. Kernel Configuration Code maturity level options Loadable module support General setup Memory technology devices Block devices Networking options ATA/IDE/MFM/RLL support SCSI support Network device support Input core support Character devices Filesystems Console drivers Sound Kernel hacking

    27. Lab (1/3) Make kernel image and download it to the target machine

    28. Lab (2/3) Steps Install giveio Download Iboot Install ToolChain Uncompress linux.tgz Edit Makefile Make Kernel Image make clean make dep make menuconfig make zImage ? arch/arm/boot/zImage

    29. Lab (3/3) Steps Make sure the bootloader is Iboot Download zImage to target machine download xmodem 0xa0002000 flashverify 0x040c0000 0xa0002000 0x100000 Download ready-made ramdisk.gz download xmodem 0xa0002000 Flashverify 0x041c0000 0xa0002000 0x500000 boot

    30. Homework Why the console seems blocked after the console display following ? "Uncompressing Linuxdone, booting the kernel."

    31. Reference The Linux Kernel Archives http://www.kernel.org/ Linux Documentation Project -The Linux Kernel http://tldp.org/LDP/tlk/tlk.html Understanding the Linux Kernel, 3rd EDITION http://www.oreilly.com/catalog/understandlk/index.html

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