Download Summary: OS Concepts System Calls

Summary: OS Concepts
• Processes
– Resources, Deadlocks
– Pipes
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Memory Management
Input/Output
Files
Security
The Shell
Concept Recycling
• layers = abstraction
• policies and
mechanisms
• user versus supervisor
(kernel) mode
– different spaces
– different levels of
executions and
privileges
– system calls (kernel)
application code
library code
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System Calls
Interface that OS provides, programs use
• set of system calls, specific to each OS
• used to transfer control of (single) CPU
– program (process) invokes => context switch
– program suspended while syscall executed
– system call wrapped in library function; e.g.,
count = read (fd, buffer, nbytes)
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Steps in Making a System Call
There are 11 steps in making the system call
read (fd, buffer, nbytes)
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System Calls (1)
• A stripped down shell:
while (TRUE) {
/* repeat forever */
type_prompt( );
/* display prompt */
read_command (command, parameters) /* input from
terminal */
if (fork() != 0) {
/* fork off child process */
/* Parent code */
waitpid( -1, &status, 0);/* wait for child to exit */
} else {
/* Child code */
execve (command, parameters, 0);/* execute command */
}
}
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System Calls (2)
• Processes have three segments: text, data, stack
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Some System Calls For Process Management
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Some System Calls For File Management
how: O_RDONLY, O_WRONLY, O_RDWR, O_CREAT
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Files and inodes
• every file denoted by unique i-number
• i-number is index into table of i-nodes
• directory: file containing a set of pairs:
– (i-number, ASCII name)
• to link is to create a new entry with the inumber of existing file
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Some System Calls For Directory Management
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System Calls (3)
(a) Two directories before linking
/usr/jim/memo to ast's directory
(b) The same directories after linking
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System Calls (4)
(a) File system before the mount
(b) File system after the mount
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Some System Calls For Miscellaneous Tasks
chmod 741 means -rwxr--x
kill -9 pid means kill process given by pid
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System Calls (5)
Some Win32 API calls
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Operating System Structure (1)
Simple structuring model for a monolithic system
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Monolithic Structure
OS = collection of procedures ~ rather than modules
(no information hiding)
Still, structure in methodology: parameters put on
stack before TRAP, for example. Three “layers”
1. Main program that invokes -- dispatches -- the
requested service procedure
2. Set of service procedures, to execute system
calls
3. Set of utility procedures, factoring common
needs of service procedures
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Operating System Structure (2)
Structure of the THE operating system
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Layered Structure in THE
5. System Operator Process
4. User processes
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I/O, console, memory, etc., taken care 0-3
3. I/O management - abstracts devices
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devices, buffers, streams
2. comm. operator - console
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above it, each proc has its own console
1. main memory & swap management
0. handle interrupts, switch processes
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multiprogramming, above it seq processes
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Operating System Structure (3)
Structure of VM/370 with CMS
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Virtual Machine VM/370
• Virtual Machine Monitor on bare HW
– offers exact copies of the underlying HW
– does not add any niceties!
• On top of VM, can have several copies of
– batch system
– single-user, interactive system CMS
• separates
– multiprogramming
– extended machine
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Operating System Structure (4)
The client-server model
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Operating System Structure (5)
The client-server model in a distributed system
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Micro-, Exo-Kernels, C-S
Insight: OS services done as user processes
– user client process requests a server process
– kernel just supports interprocess comm.
Exokernels - similar to VM, but split machine
resources (e.g., disk portions)
– saves one mapping layer (e.g., disk addresses)
– again separates multiprogramming / niceties
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OS Structure
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Monolithic Systems
Layered Systems
Virtual Machines
Exo- and Micro-kernels
– Client-Server Model
mechanisms versus policies
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Metric Units
The metric prefixes
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Other Units
• Time between slipping on a peel and
smacking the pavement = 1 bananosecond
• Half a large intestine = 1 semicolon
• Time it takes to sail 220 yards at 1 nautical
mile per hour = Knot furlong
• 1 millionth of a fish = 1 microfiche
• 1000 aches = 1 megahertz
• Basic unit of laryngitis = 1 hoarsepower
• 1 million-million microphones = 1 megaphone
• 1 million bicycles = 2 megacycles
• 2.4 statute miles of intravenous tubing at Yale
University Hospital:1 I.V. League
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