1 intro to module programming(1)

8/12/2019 1 Intro to Module Programming(1)

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Linux Device Drivers- Introduction & Basic Module Programming

A Raghavendra Rao([email protected])

C-DAC, Hyderabad
mailto:[email protected]:[email protected]


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Agenda

Kernels and Classifcations

The Linux Kernel

Linux Modules Linux Module Programming

The Kernel !m"ol Ta"le

Linux Boot Process


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Kernels and Classifcations


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#hat is a Kernel $$

Core o% the 'erating !stem

ervices (

Process Management Memor! Management

Device Management

)iles!stem Management

*et+or, Management

ecurit!


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La!out o% the Kernel


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

/e0uest made

"! the user


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

A''lication calls

s!stem li"rar!routine


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

!stem li"rar! ma,es a s!stem call


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

!stem call

Inter%ace tra'sthe ,ernel


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

Kernel access

the resources

as 'er re0uest


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

Kernel

com'letes there0uest


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

/eturns the

result


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

/eturns the result to s!stem li"rar!


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

/eturns the

result to thea''lication


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Kernel in action

A''lication

.ser

!stem Li"rar!

!stem Call

.ser'ace

Kernel

/esources

Kernel'ace

.ser re0uest

'rocessed


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1xam'le


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T!'es o% Kernel Architectures

Monolithic Kernel Micro,ernel


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Monolithic Kernel

All the 'arts o% a ,ernel li,e the cheduler2 )ile !stem2

Memor! Management2 *et+or,ing tac,s2 Device Drivers2

etc2 are maintained as a single unit +ithin the ,ernel

Advantages ( )aster Processing

Disadvantages (

Crash insecure2 'orting in3exi"ilit!2 ,ernel si4e ex'losion 1xam'les (

M-D2 .nix2 Linux2 etc


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Micro,ernel

nl! the ver! im'ortant 'arts li,e IPC2 "asic scheduler2 "asic

memor! handling2 "asic I5 'rimitives etc2 are 'ut into the

,ernel thers are maintained as server 'rocesses in user s'ace

Advantages ( Crash /esistant2 Porta"le2 maller i4e

Disadvantages (

lo+er Processing due to additional message 'assing 1xam'les (

6*72 Minix 82 1/2 Ke!K2 #indo+s *T


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The Linux Kernel

I d h L K l


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Introduction to the Linux Kernel

tarted o9 in :;;: "! Linus Torvaldsas a

sim'le terminal driver %or Intel


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Com'lete Linux !stem ( Linux Distri"utions

Bootloader ( ?/.B2 LIL2 etc

Linux Kernel

!stem Li"raries ( gli"c2 'threads2 IPC2 etc

A''lications ( +e" "ro+sers2 games2 editors2 music 'la!ers2etc


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Linux Modules

I t d ti t Li M d l


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Introduction to Linux Modules

1ach 'iece o% code that can "e added to the ,ernel

at runtime is called a module.

1ach module is made u' o% o"ect code not lin,ed

into a com'lete executa"le that can "e d!namicall!

lin,ed to the running ,ernel

The Linux ,ernel o9ers su''ort %or 0uite a %e+

di9erent t!'es or classes o% modules2 including2 "ut

not limited to2 device drivers.

lit i % th K l


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'lit vie+ o% the Kernel

D i ll L d "l M d l


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D!namicall! Loada"le Modules

/unning Linux Kernel

vmlinux

Module:,o

insmod

rmmod

module:,o

insmod

rmmod

Module:,o

insmod

rmmod

moduleE,o

insmod

rmmod


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Linux Module Programming

Introduction to Module Programming


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Introduction to Module Programming

Module initialisation (

A module al+a!s "egins +ith the %unction s'ecifed +ithin module_init().

It is the entr! 'oint o% the module

It tells the ,ernel +hat %unctionalit! does the module 'rovides

Bod! o% the module (

Per%orms the core %unctions o% the module

Calls are executed "! user-s'ace or s!stem hard+are

Module cleanu' ( A module al+a!s ends +ith the %unction s'ecifed +ithin module_exit().

1xit 'oint o% the module

It undoes +hatever initiali4ation %unction 'er%ormed

Fello #orld /evisited GG


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Fello #orld /evisitedGG

5H Basic includes H5include Jlinux5inith

include Jlinux5moduleh

5H 'eci%! the license 5

MD.L1LIC1*1?PLN

5H 'eci%! the author H5

MD.L1A.TF/CDACN



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/* Initialisation !nction */

static int ""init hello"init(void)

#

$rint%(&Hello 'orld..n)+ret!rn +

/* ention the init !nction to the %ernel */od!le"init(hello"init)+



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/* Clean!$ !nction */

static void ""e0it hello"e0it(void)

#

$rint%(&1ye or no2..n)+

/* ention the e0it !nction to the %ernel */

od!le"e0it(hello"e0it)+


The Ma,efle


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The Ma,efle

'eci%! the out'ut fle

o"-m (O helloo

etu' the varia"les

K1/*/C O 5li"5modules5shell uname -r5"uild

P#D O shell '+d

ma,e target %or com'iling the module

modules (

ma,e -C K1/*/C MOP#D modules

ma,e target %or cleaning u' the s'ace

clean (

ma,e -C K1/*/C MOP#D clean

.tilities


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.tilities

ma,e modules ( Com'iles the module 'rogram

ma,e clean( Clears the "inaries

insmod( Loads the module

mod'ro"e( Loads the module a%ter loading all the de'endenc!

modules

rmmod( .nload the module

lsmod( list all the loaded ,ernel modules 5'roc5modules modin%o( ?et the in%ormation a"out the module

de'mod( /e"uild the module de'endenc! index

The ,ernel "uild s!stem


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The ,ernel "uild s!stem

3he root Makefilestarts loo%ing or the so!rce ile in the location s$eciied by'M=PATH'o$tion.

4nce the b!ild is co$lete, the ollo2ing iles are generated 5

modulenamec( ource fle o% the module

modulenameo( Com'iled %orm o% the source fle

modulenamemodc( Contains the in%ormation a"out the module version

in%ormation2 sections2 de'endencies etc

modulenamemodo( Com'iled %orm o% modulenamemodc

modulename,o( modulenameo & modulenamemodo are lin,ed to

'roduce this fnal com'iled version o% the module

Modules!mvers( holds the in%ormation o% the ex'orted s!m"ols

modulesorder( lists out the order in +hich the com'ilation and creation o%

,o ta,es

Module Programs Qs .ser-s'ace Programs


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Module Programs Qs .ser s'ace Programs

1vent Driven 1xecution

Concurrencies

Li"raries egmentation )aults

De"ugging tac, Limitations

Module Parameters


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Module Parameters

Parameters ma! "e 'assed to the modules during moduleinsertion

The main 'ur'ose is %or ex'licit customisation o% the driver

environment The macro module_param(name, type,perm) is used to

initiali4e the 'arameters

name( *ame o% the varia"letype( argument t!'e ( "ool2 int2 char'2 etc

perm ( Permissions associated ( I/.?2 I#./

.sage


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.sage

5H Include the header H5 include Jlinux5module'aramh

5H Declare the varia"les H5

int n O :=Nchar str O FelloN

5H Declare the varia"les as module 'arameters H5

module'aramn2 int2 I/.?N

module'aramstr2 char'2 I/.?N

5H Load the module as H5

insmod 5modulename,o nOER strOFai


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The current'rocess

The current 'rocess


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The current 'rocess

The ,ernel code might execute in one o% these contexts ( Interru't Context

Process Context

Kernel threads

A glo"al 'ointer2 current 'oints to the relevant 'rocess +hen

executing in 'rocess context

The macro 'oints to the structure o% t!'e @struct tas,struct@

Jlinux5schedh +hich re'resents the 'rocess control "loc, o%linux 'rocesses

The macro is invalid +hen the code is executing in interru't context

or as a ,ernel thread

The current 'rocess


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The current 'rocess

usera''

Kernel code

(process context)

struct tas,struct Slong stateN

void Hstac,N

int 'rioN

char HcommN'idt 'idN

N

current


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The Kernel !m"ol Ta"le

The ,ernel s!m"ol ta"le


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!

The ta"le contains the addresses o% glo"al ,ernelitems ( %unctions and varia"les2 that are needed to

im'lement modulari4ed drivers

The s!m"ol ta"le can "e read "! ( cat 5'roc5,alls!ms

#hen a module is loaded2 an! s!m"ol exported"!

the module "ecomes 'art o% the ,ernel s!m"ol ta"le

*e+ modules can use the s!m"ols ex'orted "! other

modules This conce't is termed as 'module stacking'.

1xam'le ( Module tac,ing


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' g

Kernel

.B Core

.B Ke!"oard

Driver

.B Mouse

Driver

1x'orting s!m"ols


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' g !

Modules can ex'ort services to other modules using (EX!"T_#$%&!L(symol_name)macro

!m"ols must "e ex'orted in the glo"al 'art o% the

moduleUs fle2 ie2 outside o% an! %unction

!m"ols are ex'orted onl! +hen the module is

loaded

The ex'orted s!m"ol is stored in a s'ecial 'art o% the

module@s executa"le that is used used "! the ,ernel at

load time to fnd the varia"les ex'orted "! the module

.sage


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g

5H Defne the %unction to "e ex'orted

H5

void ex'ort%unc

S5H )unction "od! H5

5H 1x'ort the %unction to the ,ernel

s!m"ol ta"le H517P/TVMBLex'ort%uncN

5H )unction declaration H5

extern void ex'ort%uncN

5H Call the ex'orted %unction H5void %uncuse

S

ex'ort%uncN

1x'orting module ( ex'c Im'orting module ( im'c

.sage cont


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g

Modifcations in the Ma,efle ( Com'ile the modules together

o"-m (O ex'o im'o

Install the modules (

ma,e modulesinstall

Chec, the 'ath ( 5li"5modules5uname -r5extra

.se modproe, instead o% insmodto load im',o

mod'ro"e im'

The module ex',o +ill "e loaded 'rior to im',o

Chec, the out'ut o% lsmod.

insmod Qs mod'ro"e


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'

mod'ro"e +or,s in similar +a! as that o% insmod2 "ut italso loads an! other modules that are re0uired "! the

module !ou +ant to load

I% !our module de'ends u'on three more modules2 !ouhave to do insmod three times 'lus once %or loading

that module itsel%

But +ith mod'ro"e2 single time is suWcient It solves thede'endenc! and loads the modules +hich are re0uired

Fo+ever2 mod'ro"e searches %or modules in standard

directories2 so i% !our module is in directories other than

Fo+ mod'ro"e +or,s$


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Mod'ro"e chec,s the de'endenc! o% modules andloads those modules to resolve the de'endenc!

To ,no+ the de'endenc!2 mod'ro"e loo,s into

modules.depfle

Location o% mod'ro"ede' is 5li"5modules5uname

-r5

This fle is u'dated "! de'mod

de'mod onl! chec,s into some standard locations %or

the module o"ect fles


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Linux Boot Process

o%t+are Com'onents o% a runnning Linux Machine


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Bootloader

Kernel

/oot )iles!stem !stem Li"raries

A''lications

and much more

o%t+are Com'onents o% a runnning Linux Machine


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Bootloader Kernel

/oot )iles!stem !stem Li"raries

A''lications

and much more

The Boot 'rocess


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-- PT

-- Initialise the hard+are

tage-: Bootloader -- MB/-- Load stage-E "ootloader

BI

tage-E Bootloader-- ?/.B2 LIL2 etc

-- Load the ,ernel image "4Image

Kernel-- Decom'ress the image

-- Per%orm the initialisations ( stac,s2

'age ta"les2 etc

Po+er * 5 /eset

The Boot 'rocess cont


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-- Tem'orar! )iles!stem

-- Fel's in mounting the /)

-- 'tional

Mount the /)

Initial /AM Dis, img

Init 'rocess-- tart 5s"in5init

-- )irst user-s'ace 'rocess

A''lications

/e%erences


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Xonathan Cor"et2 Alessandro /u"ini and ?reg Kroah-Fartman2Linux Device Drivers28rd 1dition2 @/eill!

Pu"lications

Linux "oot 'rocess (htt'(55+++i"mcom5develo'er+or,s5li"rar!5l-

linux"oot5

++++i,i'ediacom

+++googlecom
http://www.wikipedia.com/http://www.wikipedia.com/


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Tank $ou )

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