SunOS--Minix

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SunOS--Minix

• A Operating System used in teaching Laboratories.
• Presented By-
• Oliver Dsouza
• Sankara Narayanan

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What we will be covering!!!

• Overview of the Minix Operating System
• The Architecture of Minix
• The Booting Process
• Implementation of System Calls How it works
• An Insight into the security
• Conclusion

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Birds Eye View of Minix

• Minix Mini Unix (Minix) basically, a UNIX
  -compatible operating system.
• Minix is small in size, with microkernel-based
  design.
• Minix has been kept (relatively) small and
  simple.
• Minix is small, it is nevertheless a preemptive,
  multitasking operating system.
• Internally, Minix is highly modular, consisting
  of several system processes organized into a
  number of independent programs.

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Continuation..

• Full multiprogramming (multiple programs can run
  at once).
• Most of the code is written is C language and the
  source code is freely available.
• Networking with TCP/IP

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Internal Architecture

• The figure represents the internal architecture
  of Minix.

Different Layers
User Processes init, login, passwd, sh, ls, cp,
cc,.. Server Processes File System (FS),
Memory Manager (MM) Kernel I/O Tasks Floppy, tty,
clock, system, Kernel Process
Management Interrupt handlers
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3
2
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Architecture Continuation..

• There are 4 layers in the Architecture
• Layers 1 to 3 comprise the Minix operating
  system, with applications running in Layer 4.
• The operating system code is linked into three
  totally separate programsmm (the memory
  manager), fs (the file system), and kernel
  (layers 1 and 2).
• Processes in layer 2 and interrupt handlers in
  layer 1 can communicate by message passing or
  shared memory all other communication is through
  message passing.

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Detailed Analysis of the Different Layers.

• Layer 1(Kernel Process Management) implements
  communicating sequential processes, thus allowing
  the remainder of Minix to be implemented as a set
  of communicating sequential processes. Layer 1 is
  a group of interrupt handlers, with its own stack
  space within kernel.
• Layer 2 (Kernel I/O Tasks) contains device driver
  processes. System provides an interface between
  kernel and the layer 3 processes.
• Layer 3 (Server Processes) contains the memory
  manager and the file system.

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Continuation.

• Layer 4 (User Processes) contains a Unix-like
  process hierarchy rooted at process 1. Every
  system call" made by a user process in layer 4 is
  converted into a message to one or other of these
  processes.

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Booting Process

• The booting process is an important one in any
  operating system. Here in Minix, the
  bootstrapping occurs in the following way,
• A small SunOS program (minix) is responsible for
  processing a configuration file, allocating
  memory for SunOS Minix, loading and relocating
  the SunOS Minix \image" and then jumping to the
  startup code within the SunOS Minix kernel
  proper.

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Continuation.

• minix allocates the requested amount of memory in
  the data segment of the SunOS process, and loads
  the image, consisting of kernel, mm, fs and init,
  at the beginning of the area allocated.
• Booting has 2 phases
• The minix Phase
• The kernel Phase

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Booting Phases.

• Booting the minix phase
• The main functions of the minix program are,
• Read the configuration file, open various devices
  on well known (to minix and kernel) SunOS
  descriptors.
• A child process is created that will run the
  Solaris minix.
• The child creates a temporary file that is the
  same size as minix physical memory and maps to
  childs address space at the virtual address
  assigned to the beginning of kernels text
  segment.
• A bootinfo structure at the start of kernel data
  segment is filled in.
• Execution then switches to kernel entry point.

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Continuation

• Booting the kernel phase
• The kernel entry point is in a small piece of
  assembler code that sets the stack pointer to
  layer 1 stack, and then calls the C function
  main(main.c).
• Then the standard pieces of code that are added
  to the boot sequence involve the setting up the
  handling of SunOS signals, and setting up of
  memory protection.

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The Important Directory Structure

• commands
• fs file system
• kernel kernel codes
• solaris
• tools
• mm memory manager

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Flow OF control

• The flow of control in minix from the user level
  the kernel level is handled by system calls.
• Minix has a set of system calls which are located
  in the table.c file.
• The fs has its own table and so the memory but
  the number of system calls is fixed

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System Call

• System call in minix is similar to a system, call
  in any system.
• A user-level process cannot directly access a
  disk. Instead it asks the kernel to obtain data
  from a file for it (the read system call).
• A user-level process cannot create another
  process. Instead, it asks the kernel to create
  one for it.

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System call

• System calls are typically made via library
  routines. Library routines are normal procedure
  calls. They perform the setup for the system
  call.
• In minix the system call functions in a similar
  fashion.

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System call

• To implement a system call in minix one needs to
  do the following steps.
• Look for a free slot in the table.c file
• Follow the standard convention
• no_sys, / 0 unused /
• do_exit, / 1 exit /
• do_fork, / 2 fork /

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System Call

• The system call would be named in the following
  manner
• do_sandbox or do_encrypt
• Once the system call method has been written its
  declaration should be mentioned in the function
  declaration header file in the file system it is
  proto.h
• _PROTOTYPE ( return type do_XXXX, (arguments if
  any) )

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System Call

• The library should also be informed about the
  system call that would be called by the user.
• The library file for the system call is written
  in the lib/other directory. The file naming
  convention is followed here it starts with an
  underscore
• Eg - _sandbox.c

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System Call

• Once the code for the system call is written in
  the "lib/other" directory a system file needs to
  be created. The system file is present in the
  "lib/sunsyscall" directory.
• A standard naming convention is followed here to.
  The filename extension is ".s".
• .global systemcallname
• systemcallname
• ba _systemcallname
• nop

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System Call

• A system call will contain a user created command
  file which when compiled creates a binary
  executable command. the command is created in the
  commands/simple directory. The file once
  compiled creates an executable binary in the
  commands/simple/bin directory.
• You will need to do a sunread to get the bin from
  the solaris system to the minix system

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System Call

• All the headers used in the system calls are kept
  in the "include" directory. The "type.h " header
  file is a very important and most useful header
  file.
• To pass a message a variable of a specific data
  type is defined, and the variable is added to the
  message structure

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System Call

• Typedef struct datatype mnYY mess_n
• n gt message number of the message
• YY gt variable name
• The size of the structure defined in the message
  is also an important factor as if the size of the
  message is increased then the system crashes

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System Call

• Typedef struct char m1sb mess_1
• define m1_sb m_u.m_m1.m1sb
• To add data in the message variable the following
  need to be done
• Message m
• m.m1_sb data