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Operating System Services and Interface for Software Development

Learn about operating system services and interface, system calls, utilities, layers, virtual machines, word processing, compilers, and more. Understand the role of system calls in programming.

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Operating System Services and Interface for Software Development

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  1. Lecture 2: OS Programming Interface • Yang, CS 170 2015

  2. What to Learn? • Operating System Services & Interface • System Calls • System utilities • OS Layers • Virtual Machines

  3. A View of Operating System Services

  4. Role of system calls Word Processing Compilers Web Browsers Email Web Servers Databases Application / Service OS Portable OS Library User System Call Interface System Portable OS Kernel Software Platform support, Device Drivers Hardware x86 PowerPC ARM PCI Ethernet 802.11 a/b/g/n SCSI IDE Graphics

  5. Linux Layers

  6. Nachos system Layers Projects 2&3 User process User process Nachos kernel threads Thread 1 Thread 2 Thread N Project 1 Nachos OS modules (Threads mgm, File System, Code execution/memory mapping, System calls/Interrupt) Simulated MIPS Machine (CPU, Memory, Disk, Console) Base Operating System (Linux for our class)

  7. OS UI: Shell Command Interpreter

  8. OS User Interface: GUI

  9. Programming API – OS System Call

  10. Standard C Library Example • C program invoking printf() library call, which calls write() system call User mode Kernel mode

  11. System Calls • System calls: Programming interface to the services provided by the OS • Mostly accessed by programs via a high-level Application Program Interface (API)rather than direct system call use • Three most common APIs are • Win32 API for Windows, • POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and • Java API for the Java virtual machine (JVM) • Why use APIs rather than system calls?

  12. System Calls • System calls: Programming interface to the services provided by the OS • Mostly accessed by programs via a high-level Application Program Interface (API)rather than direct system call use • Three most common APIs are • Win32 API for Windows, • POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and • Java API for the Java virtual machine (JVM) • Why use APIs rather than system calls? Portability. Simplicity.

  13. Types of System Calls • Process control • File management • Device management • Information maintenance • Communications • Protection

  14. Examples of Windows and Unix System Calls

  15. Transition from User to Kernel Mode

  16. I/O & Storage Layers Application / Service streams High Level I/O handles Low Level I/O registers Syscall File System descriptors I/O Driver Commands and Data Transfers Disks, Flash, Controllers, DMA

  17. Unix I/O Calls • fileHandle = open(pathName, flags) • A file handle (called file descriptor in Unix) is a small integer, pointing to a meta data structure about this file. • Pathname: a name in the file system. • Flags: read only, read/write, append etc… • errorCode = close(fileHandle) • Kernel will free the data structures associated

  18. Unix I/O Calls • byteCount = read(fileHandle, buf, count) • Read at most count bytes from the device and put them in the byte buffer buf. • Kernel can give the process fewer bytes, user process must check the byteCount to see how many were actually returned. • A negative byteCount signals an error (value is the error type) • byteCount = write(fileHandle, buf, count) • Write at most count bytes from the buffer buf • Actual number written returned in byteCount • A negative byteCount signals an error

  19. Copy file1 to file2 #command syntax: copy file1 file2 #include <stdio.h> #include <fcntl.h> #define BUF_SIZE 8192 void main(int argc, char* argv[]) { int input_fd, output_fd; int ret_in, ret_out; char buffer[BUF_SIZE]; /* Create input file descriptor */ input_fd = open (argv [1], O_RDONLY); if (input_fd == -1) { printf ("Error in openning the input file\n"); return; }

  20. copy file1 file2 /* Create output file descriptor */ output_fd = open(argv[2], O_WRONLY | O_CREAT, 0644); if(output_fd == -1){ printf ("Error in openning the output file\n"); return; } /* Copy process */ while((ret_in = read (input_fd, &buffer, BUF_SIZE)) > 0){ ret_out = write (output_fd, &buffer, ret_in); if(ret_out != ret_in){ /* Write error */ printf("Error in writing\n"); } } close (input_fd); close (output_fd); }

  21. Proj 0 Shell • A shell is a job control system • Lets user execute system utilities/applications • Windows, MacOS, Linux all have shells • Typical format: • cmd arg1 arg2 ... argn • i/o redirection <, > • filters & pipes • ls | more

  22. System Programs/Utilities • Categories of System programs/utilities • Process status and management • File /directory manipulation • File modification and text processing • Programming language support (compilers) • Program loading and execution • Communications • Application programs • Most users’ view of the operation system is defined by system programs, not the actual system calls

  23. Linux Utility Programs

  24. OS Design & Implementation • Start by defining goals and specifications • Affected by • Choice of hardware • User goals – • convenient to use, easy to learn, reliable, safe, and fast • System goals – • easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient

  25. OS Design Principles • Separate policy (what to do) and mechanism (how to do) • Why? • Layered structure • Modular • Monolithic kernel vs. Microkernel Maximize flexibility

  26. Layered Approach • The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.

  27. MS-DOS: Simple Layer Structure • written to provide the most functionality in the least space

  28. Traditional UNIX System Structure

  29. Modular approach • Object-oriented • Each core component is separate • Each talks to the others over known interfaces • Each is loadable as needed within the kernel

  30. Monolithic Kernel vs. Microkernel

  31. Microkernel System Structure • Moves as much from the kernel into “user” space • Communication takes place between user modules using message passing • Benefits: • Easier to extend a microkernel • Easier to port the operating system to new architectures • More reliable (less code is running in kernel mode) • More secure • Weakness: • Performance overhead of user space to kernel space communication

  32. Mac OS X Structure

  33. Virtual Machines • A virtual machinetakes the layered approach • A virtual machine provides an interface identical to the underlying bare hardware. • The hostcreates the illusion that each guest has its own processor and virtual memory/storage.

  34. Virtual Machines (Cont.) (a) Non-virtual machine (b) virtual machine

  35. VMware Architecture

  36. The Java Virtual Machine

  37. New OS Interface for Applications

  38. Android (Linux-based)

  39. Apple iOS Unix-based

  40. What we have learned? • Operating System Services & Interface • System Calls • System utilities • OS Layers and Virtual Machines: Discuss later

  41. Role of system calls and utilities Word Processing Compilers Web Browsers Email Web Servers Databases Application / Service System utilities OS Portable OS Library User System Call Interface System Portable OS Kernel Software Platform support, Device Drivers Hardware x86 PowerPC ARM PCI Ethernet 802.11 a/b/g/n SCSI IDE Graphics

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