Minix Kernel: MessageBased Kernel

1
Minix Kernel Message-Based Kernel
0. src/lib/posix/_fork.c 1. src/lib/other/syscall.
c
6. src/mm/main.c 7. src/mm/table.c
Memory Manager Server
(6,7)
(0,1)
User Process
do_fork
(5)
(2)
2. src/lib/i386/ Rts/_sendrec.s
Kernel
5. src/kernel/ proc.c
3. src/kernel/ mpx386.s
(3,4)
do_fork
4. src/kernel/ proc.c
2
Calling Diagram
Init
User Process
User Process
User Process
..
User Server I/O
Memory Manager
Network server
do_fork
disk
tty
clock
system
Ethernet
. do_fork Process Management
_send mini_send _receive mini_receive _sendre
c
K2p
p2K
3
vfork( )

• See do_fork() at line 16832 src/mm/forkexit.c
• v_fork does NOT do copying

parent
child
Address space

4
Lottery Scheduling

• sum_t the number of total lottery tickets
  currently holding by all the child processes

Parent process
rand() sum_t
lottery
5

3
2
n
child process
1
2
Ticket
1,2,3
4,5
5
How to add a new SysCall?

• Solution 1
• Add in a new system call from scratch
• Very complicated
• System call number usr/include/minix/callnr.h
• src/lib/posix/_newcall.c
• ...
• etc.

6
How to add a new SysCall? (contd)

• Solution 2 - a simple way
• Modify an existing system call it does something
  different with one of its parameters set to some
  special value
• For instance,
• int kill(pid_t pid, int sig)
• gt int setLotteryTickets(pid_t pid, int
  
• ticket)

negative pid