Supplement of Linux Kernel and Process Concept

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Supplement of Linux Kerneland Process Concept
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Lines of Source Code

• Linux 2 million lines
• Microsoft Windows 2000 30 million lines
• Netscape Communicator 5 17 million lines

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Linux 1.2

• Device Drivers 135000(C), 200(Assembly)
• Network 24000(C), 50 Assembly
• VFS layer 9230(C)
• 12 file systems 42000(C)
• Initialization 4000, 1600
• i387 emulation 8600, 3900
• Remainder 12000

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• Linux 1.0 165000 lines of code
• Linux 1.2 270000 C lines of code, 6000 assembly
• Linux 2.4 2 million

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Components in Linux (about OS definition)
SLOC-by-Language ansic2285657,asm144411,sh3035,
perl2022,yacc1147, tcl576,lex302,awk248,sed7
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SLOC 2437470 2065224 1837608 984076 967263 690983
Directory kernel2.4.2 mozilla XFree86-4.0.3 gcc-2
.96-20000731 gdbdejagnu-20010316 binutils-2.10.91
.0.2
cpp1279902,ansic739470,perl21220,sh13717,asm5
212, java3107,yacc1831,lex470,csh271,sed24
ansic1750460,asm35397,cpp20725,sh14666,tcl918
2, yacc3360,perl1675,lex1608,awk393,csh85,sed
57
ansic789901,cpp126738,yacc19272,sh17993,asm14
559, lisp7161,fortran3814,exp3705,objc479,sed
310,perl144
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SLOC with other systems
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The History

• Initially developed by Linus Torvalds November
  1991.
• Under GNU Public License
• Alpha, SPARC, Motorola M680x0, PowerPC, and IBM
  System/390

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Linux Versions

• A.B.C.D
• A Kernel Version, B Major Revision, C Minor
  Revision, D fix for grave errors
• 2.2.14 (Version number.release number)
• Version number Even number denotes stable
  kernel, odd number with development kernel
• Release Number Even number with stable release,
  odd number with development release

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Kernel Architecture

• Monolithic kernel versus Microkernel
• Microkernel Explicit message passing between
  different layers, slower, but easier to porting
  and making better use of RAM
• (monolithic) Kernel with loadable modules
• Object file linked to and unlinked from the
  kernel at runtime
• Runing in kernel mode of current process (instead
  of a specific process as in micokernel)

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Advantages of Modules

• Modularized
• Well-defined software interfaces to access the
  data structures
• Platform independence
• May still dependent on device, but independent of
  the hardware platform, such as IBM PC or Compaqs
  Alpha
• Memory usage load/unload on demand
• No performance penalty equivalent to the object
  code of the statically linked kernel

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Reentrant Kernel

• Reentrant function only modify local variable
  and do not alter global data structures.

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Logic Concept of CPU
CPU
Process
Virtual Memory
RAM
File
Disk
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Processes

• Programs and Processes
• Execution and address space
• Multiple execution threads in an address space
  light-weight process, thread
• Switch between user mode and kernel mode by
  system call.

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Process Implementation

• Process descriptor
• Program counter, stack pointer
• General-purpose register
• Floating point registers
• Processor control registers
• Memory management registers

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Process Address Space

• Text to be shared by several processes
• Shared memory for IPC
• mmap() to map file or device into part of the
  process address space

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Process Management

• fork(), exec(), exit(), abort()
• wait(), and zombie process
• Init
• Process groups and login sessions

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Process Descriptor (task_struct)

• Process State
• TASK_RUNNING
• TASK_INTERRUPIBLE
• TASK_UNINTERRUPTIBLE
• TASK_STOPPED
• SIGSTOP, SIGTSTP, SIGTTIN, SIGTTOU
• TASK_ZOMBIE
• wait(), wait3(), wait4(), waitpid()