1 Week 6 Intro to Kernel Modules, Project 2 Sarah Diesburg Florida State University.

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Week 6Intro to Kernel

Modules, Project 2

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/

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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

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Kernel Logistics

Where should I develop my new kernel modules? Inside /usr/src/linux-2.6.32/<module_name>/

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Kernel Modules

Or “drivers”, if you prefer…

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Kernel Module

A kernel module is a portion of kernel functionality that can be dynamically loaded into the operating system at run-time

Example USB drivers File system drivers Disk drivers Cryptographic libraries

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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.

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Creating a Kernel Module

Hello world example

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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;}

static void hello_exit(void){ printk(KERN_ALERT “Goodbye, sleepy world.\n”);}

module_init(hello_init);module_exit(hello_exit);

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Module headers





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License declaration





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Initialization function, runs when module

loaded

Tells kernel which function to

run on load





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Exit function, runs when module exits

Tells kernel which function to

run on exit

Sample Kernel Module: Makefileifneq ($(KERNELRELEASE),) obj-m := hello.o

else KERNELDIR ?= \ /lib/modules/`uname -r`/build/ PWD := `pwd`default: $(MAKE) -C $(KERNELDIR) \ M=$(PWD) modulesendif

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

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/usr/src/hello$> make

Creates hello.ko – This is the finished kernel module!

Compile the Kernel Module

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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

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Listing Modules

lsmod – lists all running modules

/usr/src/hello$>lsmod

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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…

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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 Why not?

No floating point support Segmentation fault could freeze/crash your

system Kernel ‘oops’!

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Kernel Functions

printk() instead of printf() kmalloc() instead of malloc() kfree() instead of free()

Where can I find definitions of these kernel functions?

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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

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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/string.h> /* string functions! */

Look inside linux-2.6.32/include/ for more… Google is also your friend

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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

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Project 2: /Proc Kernel Module and Elevator

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procfs Kernel Module

procfs “hello world” example Creates a read-only procfs entry

Steps 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 F

S

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Procfs: Headers and Global Data#include <linux/module.h>

#include <linux/kernel.h>

#include <linux/proc_fs.h>

MODULE_LICENSE(“GPL”);

#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);

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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->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;}

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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;}

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Procfs: Deletion

void hello_proc_exit(void)

{

remove_proc_entry(ENTRY_NAME, NULL);

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

}

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Procfs: Registration

module_init(hello_proc_init);

module_exit(hello_proc_exit);

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Testing Procfs

$> sudo insmod hello_proc.ko

$> sudo tail /var/log/syslog

$> cat /proc/helloworld

$> sudo rmmod hello_proc

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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…

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Part 3: Elevator Scheduling

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Part 3: Elevator Scheduling Implement a kernel module that simulates an

elevator system Implement system calls to interact with your

elevator Implement a procfs entry to display

debugging information Test using a set of user-space programs to

exercise your system

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Why Elevator Scheduling?

Classic producer/consumer analogy Similar to disk elevators

File system produces read/write requests Disk consumes requests, optimized for disk head

position, rotational delays, etc.

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Your Elevator

One elevator Five floors Four types of people

Adults Children Delivery people Maintenance people

The elevator cannot exceed its maximum weight load

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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 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

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Passengers will line up (FIFO)

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Each passenger has a destination floor in mind…

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I want to go to

floor 3

The elevator must be started to service passengers…

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Start!

The elevator must be started to service passengers…

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Elevator starts on the

first floor

Passengers enter in FIFO order

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Make sure passengers don’t

exceed weight limit!

Passengers enter in FIFO order

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More passengers can be queuing

up!

Elevator can move to any floor

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Going to floor 3!

Red and black has destination floor 3, blue has

destination floor 2


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Must take certain amount of time

between floors…


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between floors…


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between floors…


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between floors…


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between floors…

Passengers disappear when they exit…

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Elevator stop in progress…

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Must finish delivering

passengers before stopping…

Stop in Progress


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Stop in Progress


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Stop in Progress

Elevator stop

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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)

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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

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

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Elevator Test Applications

consumer.c Runs in infinite loop Issues K passenger requests once per second

producer.c Takes an argument telling the elevator to start or

stop

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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

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Additional Design Considerations How to move elevator? How to protect the floor FIFO queues? What scheduling algorithm to use?

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Next Time

Kernel debugging techniques How to insert system calls Some elevator scheduling algorithms

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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 elevator and floor queue data

structures

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1 Week 6 Intro to Kernel Modules, Project 2 Sarah Diesburg Florida State University.

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