Week 6 Intro to Kernel Modules, Project 2diesburg/courses/cop4610_fall10/week06/... · 2012-08-04 · Intro to Kernel Modules, Project 2 1 Sarah Diesburg Florida State University

Week 6

Intro to Kernel Modules,

Project 2

1

Sarah Diesburg

Florida State University

Kernel Logistics

� Where should I put the kernel source?

� /usr/src/

� Creates /usr/src/linux-2.6.32/

� Where do I issue kernel building commands

(e.g. ‘make oldconfig’, ‘make menuconfig’,

‘make’, …)?

� Inside /usr/src/linux-2.6.32/

2

Kernel Logistics

� Where is the kernel image installed?

� Inside /boot/

� Starts with vmlinuz…

� Where does the initramfs image go?

� Inside /boot/

� Where is the grub file?

� /boot/grub/menu.lst

3

Kernel Logistics

� Where should I develop my new kernel

modules?

� Inside /usr/src/linux-2.6.32/<module_name>/

4

Kernel Modules

Or “drivers”, if you prefer…

5

Kernel Module

� A kernel module is a portion of kernel

functionality that can be dynamically loaded

into the operating system at run-time

� Example� Example

� USB drivers

� File system drivers

� Disk drivers

� Cryptographic libraries

6

Why not just compile everything

into the kernel?� Each machine only needs a certain number

of drivers

� For example, should not have to load every single motherboard driver

� Load only the modules you need

� Smaller system footprint

� Dynamically load modules for new devices

� Camera, new printer, etc.

7

Creating a Kernel Module

� Hello world example

8

Sample Kernel Module: hello.c

#include <linux/init.h>

#include <linux/module.h>

MODULE_LICENSE(“Dual BSD/GPL”);

static int hello_init(void)

{

printk(KERN_ALERT “Hello, world!\n”);

return 0;return 0;

}

static void hello_exit(void)

{

printk(KERN_ALERT “Goodbye, sleepy world.\n”);

}

module_init(hello_init);

module_exit(hello_exit);

9






{


return 0;

Module headers

return 0;

}


{


}



10






{


return 0;

License

declaration

return 0;

}


{


}



11






{


return 0;

Initialization

function, runs

when module

loaded

return 0;

}


{


}



12

Tells kernel which

function to run on

load






{


return 0;return 0;

}


{


}



13

Exit function, runs

when module exits

Tells kernel which

function to run on

exit

Sample Kernel Module: Makefile

ifneq ($(KERNELRELEASE),)

obj-m := hello.o

else

KERNELDIR ?= \

/lib/modules/`uname -r`/build//lib/modules/`uname -r`/build/

PWD := `pwd`

default:

$(MAKE) -C $(KERNELDIR) \

M=$(PWD) modules

endif

clean:

rm -f *.ko *.o Module* *mod*

14

/usr/src/hello$> make

� Creates hello.ko – This is the finished kernel

module!

Compile the Kernel Module

module!

15

Inserting and Removing the Module

� insmod – insert a module

/usr/src/hello$> sudo insmod hello.ko

� rmmod – remove a module

/usr/src/hello$> sudo rmmod hello.ko

16

Listing Modules

� lsmod – lists all running modules

/usr/src/hello$>lsmod

17

Where is it printing?

� Look inside /var/log/syslog

� Hint – to watch syslog in realtime, issue the

following command in a second terminal:

$> sudo tail –f /var/log/syslog

� Demo…

18

Kernel Module vs User Application

� All kernel modules are event-driven� Register functions

� Wait for requests and service them

� Server/client model

� No standard C library� No standard C library� Why not?

� No floating point support

� Segmentation fault could freeze/crash your system� Kernel ‘oops’!

19

Kernel Functions

� printk() instead of printf()

� kmalloc() instead of malloc()

� kfree() instead of free()

� Where can I find definitions of these kernel

functions?

20

Kernel manpages

� Section 9 of manpages

� Must install manually for our development

kernel

$> wget http://ftp.us.debian.org/debian/pool/main/l/linux-

2.6/linux-manual-2.6.32_2.6.32-22_all.deb

$> sudo dpkg –i linux-manual-2.6.32_2.6.32-22_all.deb

21

Kernel Headers

� #include <linux/init.h> /* module stuff */

� #include <linux/module.h> /* module stuff */

� #include <asm/semaphore.h> /* locks */

#include <linux/list.h> /* linked lists */� #include <linux/list.h> /* linked lists */

� #include <linux/string.h> /* string functions! */

� Look inside linux-2.6.32/include/ for more…

� Google is also your friend

22

How can I explore the kernel?

� Use lxr (“Linux Cross Referencer”):

� http://lxr.linux.no/

� Select your kernel version and enter search terms

� Use grep on your kernel source

$> grep –Rn xtime /usr/src/linux-

2.6.32

� R = recursive, n = display line number

23

Project 2: /Proc Kernel

Module and Elevator

24

procfs Kernel Module

� procfs “hello world” example

� Creates a read-only procfs entry

� Steps

� Create entry in module_init function� Create entry in module_init function

� Register reading function with procfs_read

� Delete entry in module_cleanup function

� Reference

� Linux Kernel Module Programming Guide: Proc FS

25

Procfs: Headers and Global Data


#include <linux/kernel.h>

#include <linux/proc_fs.h>

MODULE_LICENSE(“GPL”);

#define ENTRY_NAME “helloworld”#define ENTRY_NAME “helloworld”

#define PERMS 0644

#define PARENT NULL

struct proc_dir_entry *proc_entry;

int procfile_read(char *buf, char **buf_location, off_t

offset, int buffer_length, int *eof, void *data);

26

Procfs: Creation

int hello_proc_init(void)

{

proc_entry =

create_proc_entry(ENTRY_NAME,

PERMS,PARENT);

/* check proc_entry != NULL */

proc_entry->read_proc = procfile_read;proc_entry->read_proc = procfile_read;

proc_entry->mode = S_IFREG | S_IRUGO;

proc_entry->uid = 0;

proc_entry->gid = 0;

proc_entry->size = 11;

printk(“/proc/%s created\n”, ENTRY_NAME);

return 0;

}

27

Procfs: Reading

int procfile_read(char *buf, char **buf_location, off_t offset, int buffer_length, int *eof, void *data)

{

int ret;

printk(“/proc/%s read called.\n”, ENTRY_NAME);

/* Setting eof. We exhaust all data in one shot */

*eof = 1;

ret = sprintf(buf, “Hello World!\n”);

return ret;

}

28

Procfs: Deletion

void hello_proc_exit(void)

{

remove_proc_entry(ENTRY_NAME, NULL);

printk(“Removing /proc/%s.\n”, ENTRY_NAME);

}

29

Procfs: Registration

module_init(hello_proc_init);

module_exit(hello_proc_exit);

30

Testing Procfs

$> sudo insmod hello_proc.ko

$> sudo tail /var/log/syslog

$> cat /proc/helloworld

$> sudo rmmod hello_proc$> sudo rmmod hello_proc

31

Part 2: Kernel Time

� Implement a procfs entry to display the value

of xtime

� Hint: You may not be able to directly read xtime from your module, but maybe something else can…

32

Part 3: Elevator Scheduling

33

Part 3: Elevator Scheduling

� Implement a kernel module that simulates an

elevator system

� Implement system calls to interact with your

elevatorelevator

� Implement a procfs entry to display

debugging information

� Test using a set of user-space programs to

exercise your system

34

Why Elevator Scheduling?

� Classic producer/consumer analogy

� Similar to disk elevators

� File system produces read/write requests

� Disk consumes requests, optimized for disk head � Disk consumes requests, optimized for disk head position, rotational delays, etc.

35

Your Elevator

� One elevator

� Five floors

� Four types of people

� Adults� Adults

� Children

� Delivery people

� Maintenance people

� The elevator cannot exceed its maximum

weight load

36

Your Elevator

� People will line up at each floor in a first-in,

first-out (FIFO) order

� Each person has a starting floor and a

destination floordestination floor

� The elevator must pause for a period of time

to collect people and move between floors

� Once the elevator reaches a passenger’s

destination floor, that passenger gets out and

ceases to exist

37

Passengers will line up (FIFO)

38

Each passenger has a destination floor

in mind…

39

I want

to go to

floor 3

The elevator must be started to service

passengers…

40

Start!

The elevator must be started to service

passengers…

41

Elevator

starts on the

first floor

Passengers enter in FIFO order

42

Make sure

passengers don’t

exceed weight

limit!

Passengers enter in FIFO order

43

More passengers

can be queuing

up!

Elevator can move to any floor

44

Going to floor 3!

Red and black

has destination

floor 3, blue has

destination floor 2


45

Must take certain

amount of time

between floors…


46

Must take certain

amount of time

between floors…


47

Must take certain

amount of time

between floors…


48

Must take certain

amount of time

between floors…


49

Must take certain

amount of time

between floors…

Passengers disappear when they exit…

50

Elevator stop in progress…

51

Must finish

delivering

passengers

before stopping…

Stop in

Progress


52

Must finish

delivering

passengers

before stopping…

Stop in

Progress


53

Must finish

delivering

passengers

before stopping…

Stop in

Progress

Elevator stop

54

Full stop

Controlling the Elevator

Implement the following system calls

� int start_elevator(void)

� int issue_request(int passenger_type, int

start_floor, int destination_floor)

� int stop_elevator(void)

55

Elevator Scheduling Algorithms

� A scheduling algorithm considers the state of

the consumers and all requests and tries to

optimize some metric

� Throughput: Maximize total requests, minimize � Throughput: Maximize total requests, minimize processing total time.

� Priorities: Requests now have deadlines. Maximize number of requests meeting deadlines.

� Burst throughput: Maximize peak requests that can be handled.

� Energy: Minimize consumer action

56

Elevator Test Applications

� consumer.c

� Runs in infinite loop

� Issues K passenger requests once per second

� producer.c� producer.c

� Takes an argument telling the elevator to start or stop

57

Kernel Time Constraints

#include <linux/delay.h>

void ssleep(unsigned int seconds);

� A call to ssleep will have the program cease

to the task scheduler for seconds number of

seconds

58

Additional Design Considerations

� How to move elevator?

� How to protect the floor FIFO queues?

� What scheduling algorithm to use?

59

Next Time

� Kernel debugging techniques

� How to insert system calls

� Some elevator scheduling algorithms

60

What you should do?

� Finish part 1 (5 system calls)

� Finish part 2 (/proc module)

� Try sample kernel module and proc module

Make skeleton part 3 module� Make skeleton part 3 module

� Make elevator and floor queue data

structures

61

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Week 6 Intro to Kernel Modules, Project 2diesburg/courses/cop4610_fall10/week06/... · 2012-08-04 · Intro to Kernel Modules, Project 2 1 Sarah Diesburg Florida State University