Memory Allocation:

• fork()
• exec()

MINIX directory:
                        usr
                       /  \
                      /    \
                 include   src
                 /  |  \     |
                  minix      kernel
                    |         |
                  type.h      proc.h
                  (p.558)     (p.581)
           (message definition)

Page 558: type.h  (handle message passing)

• m_u is a member of the message structure.
• the m_u structure is a block memory which can handle the largest of these six message types.  But it can only handles one at a time. (union type)
• e.g.  Difference between "struct" and "union":

 

struct  foo {    double a;    int b;    char c; }; struct foo bar;

union  foo2 {    double a;    int b;    char c; }; union foo2 bar2;

struct:   The addresses of a, b, and c are sequential located.  They have different offsets.
union:    a, b, and c are stored only one at a time.  They have same offsets.  This example the size of bar2 is same as the size of double.

In MINIX, we actually have process table divided into 3 parts.

• the kernel may contain 1 process table

(Scheduling, context switching, message passing)
• memory management contains the second process table

(where the mm process locate)
• file system is the third table

(file process open, which position is in the current file)

These three tables are parallelly operated.
i.e. The positions n of the arrays of the kernel, mm, file process tables refer to the same process.

kernel            mm              FS

(n)	(n)	(n)

All elements of index n describe the same process.
Identify process:

-  index of array
- process ID #

Page 591 MINIX (assembly part)
Once the bootstrap process has loaded the O.S. into memory, control is transferred to the lable MINIX.

Page 601 main
Initialize t as-NR_TASKS (task's number).  We want the tasks have negative label and normal process has positive label.
In C, a[i] is just another way of writing *(a+i).

wants                                              gets

User Precesses                                Servers

0

-1

-2

-3                                Tasks   -NR_TASKS                                  0

Page 602, lines 06785 to 06790:  (Set Registers)

  rp->p_map[T].mem_len  = text_clicks;
 rp->p_map[D].mem_phys = text_base + text_clicks;
 rp->p_map[D].mem_len  = data_clicks;
 rp->p_map[S].mem_phys = text_base + text_clicks + data_clicks;
 rp->p_map[S].mem_vir  = data_clicks; /* empty - stack is in data */
 
 

Stack (grow downward)

Data (grow upward)

Text (Codes)    (Two processes may read the same program)

Store registers.

Entry for hardware interrupt.   Get control from process.

Entry for software interrupt.

• Application issue system call.
• All system call handle by servers.
• Part of kernel function is handling passing message.
• Send message to task to satisfy that request.
• Let server make sure this request is done.  There is no problem.
• System calls in minix are treated as interrupt form.

Check deadlock.

Page 609 ready

Page 608 pick-proc