Operating System Services
Operating Systems
Spring 2009-2010
CS5212
Operating System Services
Outline
1
Operating System Services
System Calls
Types of System Calls
CS5212
Operating System Services
System Calls
Types of System Calls
Outline
1
Operating System Services
System Calls
Types of System Calls
CS5212
Operating System Services
System Calls
Types of System Calls
Implementing System Calls
A typical way to implement system calls is to use a
software interrupt. Interrupts transfer control to the kernel
so software simply needs to
Set up some register with the system call number they want
and execute the software interrupt
Typically, System-Call Interface maintains a table with the
numbers of the system calls
CS5212
Operating System Services
System Calls
Types of System Calls
Interrupts
An interrupt is
1
2
an asynchronous signal from hardware to CPU indicating
the need for attention
a synchronous event in software being executed indicating
the need for a change in execution
A hardware interrupt causes the processor to save its state
of execution via a context switch, and begin execution of an
interrupt handler
Software interrupts (aka traps, exceptions) are usually
implemented as instructions in the instruction set of the
CPU, which cause a context switch to an interrupt handler
similar to a hardware interrupt
caused either by an error or a user request
CS5212
Operating System Services
System Calls
Types of System Calls
System Call Parameter Passing
Three general methods used to pass parameters to the OS
Simplest: pass the parameters in registers
...but what if there are more parameters than registers?
Parameters stored in a block, or table, in memory, and
address of block passed as a parameter in a register
Each individual system call knows how to treat the table
contents
This approach taken by Linux and Solaris
Parameters placed, or pushed, onto the stack by the
program and popped off the stack by the operating system
Block and stack methods do not limit the number or length
of parameters being passed
CS5212
Operating System Services
System Calls
Types of System Calls
Parameter Passing via Table
CS5212
Operating System Services
System Calls
Types of System Calls
Outline
1
Operating System Services
System Calls
Types of System Calls
CS5212
Operating System Services
System Calls
Types of System Calls
Categories
Process control
File management
Device management
Information maintenance
Communications
CS5212
Operating System Services
System Calls
Types of System Calls
Process Control
end, abort
load, execute
create process, terminate process
get/set process attributes
wait for time
wait/signal event
allocate and free memory
CS5212
Operating System Services
System Calls
Types of System Calls
File Management
create/delete file
open, close
read, write, reposition
get/set file attributes
CS5212
Operating System Services
System Calls
Types of System Calls
Device Management
request device, release device
read, write, reposition
get/set device attributes
logically attach or detach devices
CS5212
Operating System Services
System Calls
Types of System Calls
Information Maintenance
get/set time or date
get/set system data
number of current users
amount of free memory
(numerous other statistics)
CS5212
Operating System Services
System Calls
Types of System Calls
Communication
create, delete communication connection
send, receive messages
transfer status information
attach or detach remote devices
CS5212
Operating System Services
System Calls
Types of System Calls
Tasks for Further Investigation
Software interrupts
File Descriptors
System Stack
CS5212