Working with the Unix OS

Introduction to kernel
}
{
printf("can't create file %s\n", argv[2]);
exit(1);
}
copy (fdold, fdnew);
exit(0);
copy(int old, int new)
{
int count;
while ((count = read(old, buffer, sizeof(buffer))) > 0)
write (new, buffer, count);
}
UNIX system can execute in two modes, kernel or user, it uses a separate stack for each mode.
The user stack contains the arguments, local variables, and other data for functions executing in user mode.
The kernel stack of a process is null when the process executes in user mode.
! User and
Kernel
Stack
for Copy
Program
User Stack Kernel Stack
local not
vars shown
addr of frame 2
ret addr after write
params new
to
buffer
write count
local count
vars
addr of frame 1
ret addr after copy
params old
to
new
copy
local count
vars
addr of frame 0
ret addr after main
params argc
to
argv
main
frame 3
call
write()
frame 2
call
write()
frame 1
call
main()
local
vars
addr of frame 1
ret addr after func2
params func2
to
kernel
local
vars
addr of frame 0
ret addr after func1
params func1
to
kernel
frame 3
frame 2
call
func2()
frame 1
call
func1()
start frame 0 system call interface frame 0
Data Structures for Processes
Every process has an entry in the kernel process table. Each process is allocated a u area (private data manipulated
only by the kernel).
The process table contains pointers to a per process region table, whose entries point to entries in a region table. A
region is a contiguous area of a process's address space, such as text, data and stack.
Region table entries describe the attributes of the region, whether it contains text or data, whether it is shared or
private, and where the "data" of the region is located in memory.
When a process invokes. "fork", the kernel duplicates the address space of the old process, allowing processes to
share regions when possible and making a physical copy otherwise.
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