Hello World Kernel Module

[muks]

Hey i(Fedora Newbie) have Fedora 7 (Kernel: 2.6.23.12-52.fc7). I am following book titled " The Linux Kernel Module Programming Guide". I tried to compile the Hello World Kernel Module and got an error. Please go through the source code & error and let me know where i m wrong.

Source Code:
------------------

[root@localhost 02-HelloWorld]# cat hello-1.c 
#include <linux/module.h>
#include <linux/kernel.h>

int init_module(void)
{
printk(KERN_INFO "Hello world 1.\n");
return 0;
}

void cleanup_module(void)
{
printk(KERN_INFO "Goodbye world 1.\n");
}
[root@localhost 02-HelloWorld]#

Makefile
----------

[root@localhost 02-HelloWorld]# cat Makefile 
obj-m += hello-1.c

all:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
[root@localhost 02-HelloWorld]#

Error
------

[root@localhost 02-HelloWorld]# make
make -C /lib/modules/2.6.23.12-52.fc7/build M=/home/mukul/Desktop/lkmpg-examples/02-HelloWorld modules
make[1]: Entering directory `/usr/src/kernels/2.6.23.12-52.fc7-i686'
scripts/Makefile.build:223: target `/home/mukul/Desktop/lkmpg-examples/02-HelloWorld/hello-1.c' doesn't match the target pattern
  Building modules, stage 2.
  MODPOST 0 modules
make[1]: Leaving directory `/usr/src/kernels/2.6.23.12-52.fc7-i686'
[root@localhost 02-HelloWorld]#

[stevea]

This

obj-m += hello-1.c

should be this

obj-m += hello-1.o

[muks]

should be this

obj-m += hello-1.o

Thanks a lot. Couldn't c that print mistake.

Can you also tell me where i can read about "printk()" function and KERN_INFO etc....

[CaesarRupus]

Hi,

I have the same problem and mine is .o .



root@abhirup-laptop:/home/abhirup/Documents/kernel# ls
hello-1.c Makefile modules.order Module.symvers
root@abhirup-laptop:/home/abhirup/Documents/kernel# cat hello-1.c


/*
* hello−1.c − The simplest kernel module.
*/
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_INFO */
int init_module(void)
{
printk(KERN_INFO "Hello world 1.\n");
/*
* A non 0 return means init_module failed; module can't be loaded.
*/
return 0;
}
void cleanup_module(void)
{
printk(KERN_INFO "Goodbye world 1.\n");
}
root@abhirup-laptop:/home/abhirup/Documents/kernel# cat Makefile
obj−m += hello−1.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
root@abhirup-laptop:/home/abhirup/Documents/kernel# make
make -C /lib/modules/2.6.32-21-generic/build M=/home/abhirup/Documents/kernel modules
make[1]: Entering directory `/usr/src/linux-headers-2.6.32-21-generic'
Building modules, stage 2.
MODPOST 0 modules
make[1]: Leaving directory `/usr/src/linux-headers-2.6.32-21-generic'
root@abhirup-laptop:/home/abhirup/Documents/kernel#

[vineetmadan]

NUmber 1 : The error is in your makefile.
FOR obj-m += hello-1.c READ obj-m += hello-1.o

Number 2: Even if it is .o mentioned be sure that u have not prepared the makefile by copy pasting from some example . type it yourself with special care after line
all:
<tab>START WRITING HERE... mind it is not space. but the monent you press enter after "all:" you come on a new line. press a tab there and then write the execution line
<tab> make -C .............. modules
clean:
<tab> make -C ........ clean

Your error will surely get resolved... if there is no other error prob is with making of Makefile.

regards


Makefile
----------
[CODE][root@localhost 02-HelloWorld]# cat Makefile
obj-m += hello-1.c

all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

------

[root@localhost 02-HelloWorld]# make
make -C /lib/modules/2.6.23.12-52.fc7/build M=/home/mukul/Desktop/lkmpg-examples/02-HelloWorld modules
make[1]: Entering directory `/usr/src/kernels/2.6.23.12-52.fc7-i686'
scripts/Makefile.build:223: target `/home/mukul/Desktop/lkmpg-examples/02-HelloWorld/hello-1.c' doesn't match the target pattern
  Building modules, stage 2.
  MODPOST 0 modules
make[1]: Leaving directory `/usr/src/kernels/2.6.23.12-52.fc7-i686'
[root@localhost 02-HelloWorld]#

[/QUOTE]

[sandhyaprasadk]

@vineetmadan
Thank you very much.
I faced the same problem.
I resolved successfully with the help of your nice explanation.

[fpmurphy]

Can you also tell me where i can read about "printk()" function and KERN_INFO etc...

The kernel print function, printk(), behaves almost identically to the C library printf() function. Indeed, throughout this book we have not made use of any real differences. For most intentions, this is fine; printk() is simply the name of the kernel's formatted print function. It does have some differences, however.

The major difference between printk() and printf() is the capability of the former to specify a loglevel. The kernel uses the loglevel to decide whether to print the message to the console. The kernel displays all messages with a loglevel below a specified value on the console.

The log levels are

KERN_EMERG An emergency condition; the system is probably dead
KERN_ALERT A problem that requires immediate attention
KERN_CRIT A critical condition
KERN_ERR  An error
KERN_WARNING  A warning
KERN_NOTICE  A normal, but perhaps noteworthy, condition
KERN_INFO  An informational message
KERN_DEBUG  A debug messagetypically superfluous

For information about the format options available in printk see http://www.kernel.org/doc/Documentat...tk-formats.txt