SunOS--Minix

1. SunOS--Minix A Operating System used in teaching Laboratories. Presented By:- Oliver Dsouza Sankara Narayanan

2. 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

3. Bird’s 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.

4. 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

5. 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 4 3 2 1

6. 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 programs|mm (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.

7. 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.

8. 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.

9. 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.

10. 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

11. 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 child’s address space at the virtual address assigned to the beginning of kernel’s text segment. • A bootinfo structure at the start of kernel data segment is filled in. • Execution then switches to kernel entry point.

12. 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.

13. The Important Directory Structure • commands • fs – file system • kernel – kernel codes • solaris • tools • mm – memory manager

14. 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

15. 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.

16. 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.

17. 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 */

18. 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) );

19. 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

20. 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

21. 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

22. 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

23. System Call • Typedef struct { datatype mnYY; } mess_n; n => message number of the message YY => 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

24. 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