Developers

Device Drivers, Part 2: Writing Your First Linux Driver in the Classroom

December 1, 2010

53949

This article, which is part of the series on Linux device drivers, deals with the concept of dynamically loading drivers, first writing a Linux driver, before building and then loading it.

Shweta and Pugs reached their classroom late, to find their professor already in the middle of a lecture. Shweta sheepishly asked for his permission to enter. An annoyed Professor Gopi responded, “Come on! You guys are late again; what is your excuse, today?”

Pugs hurriedly replied that they had been discussing the very topic for that day’s class — device drivers in Linux. Pugs was more than happy when the professor said, “Good! Then explain about dynamic loading in Linux. If you get it right, the two of you are excused!” Pugs knew that one way to make his professor happy was to criticise Windows.

He explained, “As we know, a typical driver installation on Windows needs a reboot for it to get activated. That is really not acceptable; suppose we need to do it on a server? That’s where Linux wins. In Linux, we can load or unload a driver on the fly, and it is active for use instantly after loading. Also, it is instantly disabled when unloaded. This is called dynamic loading and unloading of drivers in Linux.”

This impressed the professor. “Okay! Take your seats, but make sure you are not late again.” The professor continued to the class, “Now you already know what is meant by dynamic loading and unloading of drivers, so I’ll show you how to do it, before we move on to write our first Linux driver.”

Dynamically loading drivers

These dynamically loadable drivers are more commonly called modules and built into individual files with a .ko (kernel object) extension. Every Linux system has a standard place under the root of the file system (/) for all the pre-built modules. They are organised similar to the kernel source tree structure, under /lib/modules/<kernel_version>/kernel, where <kernel_version> would be the output of the command uname -ron the system, as shown in Figure 1.

To dynamically load or unload a driver, use these commands, which reside in the /sbin directory, and must be executed with root privileges:

lsmod — lists currently loaded modules
insmod <module_file> — inserts/loads the specified module file
modprobe <module> — inserts/loads the module, along with any dependencies
rmmod <module> — removes/unloads the module

Let’s look at the FAT filesystem-related drivers as an example. Figure 2 demonstrates this complete process of experimentation. The module files would be fat.ko, vfat.ko, etc., in the fat (vfat for older kernels) directory under /lib/modules/`uname -r`/kernel/fs. If they are in compressed .gz format, you need to uncompress them with gunzip, before you can insmodthem.

The vfat module depends on the fat module, so fat.ko needs to be loaded first. To automatically perform decompression and dependency loading, use modprobe instead. Note that you shouldn’t specify the .ko extension to the module’s name, when using the modprobe command. rmmod is used to unload the modules.

Our first Linux driver

Before we write our first driver, let’s go over some concepts. A driver never runs by itself. It is similar to a library that is loaded for its functions to be invoked by a running application. It is written in C, but lacks a main() function. Moreover, it will be loaded/linked with the kernel, so it needs to be compiled in a similar way to the kernel, and the header files you can use are only those from the kernel sources, not from the standard /usr/include.

One interesting fact about the kernel is that it is an object-oriented implementation in C, as we will observe even with our first driver. Any Linux driver has a constructor and a destructor. The module’s constructor is called when the module is successfully loaded into the kernel, and the destructor when rmmod succeeds in unloading the module. These two are like normal functions in the driver, except that they are specified as the init and exit functions, respectively, by the macros module_init() and module_exit(), which are defined in the kernel header module.h.

/* ofd.c – Our First Driver code */
#include <linux/module.h>
#include <linux/version.h>
#include <linux/kernel.h>

static int __init ofd_init(void) /* Constructor */
{
    printk(KERN_INFO "Namaskar: ofd registered");
    return 0;
}

static void __exit ofd_exit(void) /* Destructor */
{
    printk(KERN_INFO "Alvida: ofd unregistered");
}

module_init(ofd_init);
module_exit(ofd_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Anil Kumar Pugalia <email_at_sarika-pugs_dot_com>");
MODULE_DESCRIPTION("Our First Driver");

Given above is the complete code for our first driver; let’s call it ofd.c. Note that there is no stdio.h (a user-space header); instead, we use the analogous kernel.h (a kernel space header). printk() is the equivalent of printf(). Additionally, version.h is included for the module version to be compatible with the kernel into which it is going to be loaded. The MODULE_* macros populate module-related information, which acts like the module’s “signature”.

Building our first Linux driver

Once we have the C code, it is time to compile it and create the module file ofd.ko. We use the kernel build system to do this. The following Makefile invokes the kernel’s build system from the kernel source, and the kernel’s Makefile will, in turn, invoke our first driver’s Makefile to build our first driver.

To build a Linux driver, you need to have the kernel source (or, at least, the kernel headers) installed on your system. The kernel source is assumed to be installed at /usr/src/linux. If it’s at any other location on your system, specify the location in the KERNEL_SOURCE variable in this Makefile.

# Makefile – makefile of our first driver

# if KERNELRELEASE is defined, we've been invoked from the
# kernel build system and can use its language.
ifneq (${KERNELRELEASE},)
    obj-m := ofd.o
# Otherwise we were called directly from the command line.
# Invoke the kernel build system.
else
    KERNEL_SOURCE := /usr/src/linux
    PWD := $(shell pwd)
default:
    ${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} modules

clean:
    ${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} clean
endif

With the C code (ofd.c) and Makefile ready, all we need to do is invoke make to build our first driver (ofd.ko).

$ make
make -C /usr/src/linux SUBDIRS=... modules
make[1]: Entering directory `/usr/src/linux'
  CC [M]  .../ofd.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      .../ofd.mod.o
  LD [M]  .../ofd.ko
make[1]: Leaving directory `/usr/src/linux'

Summing up

Once we have the ofd.ko file, perform the usual steps as the root user, or with sudo.

# su
# insmod ofd.ko
# lsmod | head -10

lsmod should show you the ofd driver loaded.

While the students were trying their first module, the bell rang, marking the end of the session. Professor Gopi concluded, “Currently, you may not be able to observe anything other than the lsmod listing showing the driver has loaded. Where’s the printk output gone? Find that out for yourselves, in the lab session, and update me with your findings. Also note that our first driver is a template for any driver you would write in Linux. Writing a specialised driver is just a matter of what gets filled into its constructor and destructor. So, our further learning will be to enhance this driver to achieve specific driver functionalities.”

hi, i have to change the system after above comment and missed to see the link on that system.

now i am using
Linux sunils 3.2.0-23-generic #36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

my code compiled with this with make file
obj-m += ofd.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

and when looking at the lib/modules/…/buld i find as below. but source link (/build/buildd/linux-3.2.0) was red colored(dont know why) and when looking what it points to i found that there is no such directory(but still i got my module compiled)

total 1088

drwxr-xr-x 7 root root 4096 Jul 2 13:54 ./

drwxr-xr-x 5 root root 4096 Jun 26 16:05 ../

drwxr-xr-x 3 root root 4096 Apr 25 2012 arch/

lrwxrwxrwx 1 root root 31 May 31 16:57 block -> ../linux-headers-3.2.0-23/block/

-rw-r–r– 1 root root 140241 Jul 2 13:53 .config

-rw-r–r– 1 root root 140241 Jul 2 12:25 .config.old

lrwxrwxrwx 1 root root 32 May 31 16:57 crypto -> ../linux-headers-3.2.0-23/crypto/

lrwxrwxrwx 1 root root 39 May 31 16:57 Documentation -> ../linux-headers-3.2.0-23/Documentation/

lrwxrwxrwx 1 root root 33 May 31 16:57 drivers -> ../linux-headers-3.2.0-23/drivers/

lrwxrwxrwx 1 root root 34 May 31 16:57 firmware -> ../linux-headers-3.2.0-23/firmware/

lrwxrwxrwx 1 root root 28 May 31 16:57 fs -> ../linux-headers-3.2.0-23/fs/

drwxr-xr-x 5 root root 4096 Apr 25 2012 include/

lrwxrwxrwx 1 root root 30 May 31 16:57 init -> ../linux-headers-3.2.0-23/init/

lrwxrwxrwx 1 root root 29 May 31 16:57 ipc -> ../linux-headers-3.2.0-23/ipc/

lrwxrwxrwx 1 root root 32 May 31 16:57 Kbuild -> ../linux-headers-3.2.0-23/Kbuild

lrwxrwxrwx 1 root root 33 May 31 16:57 Kconfig -> ../linux-headers-3.2.0-23/Kconfig

drwxr-xr-x 2 root root 4096 Jul 2 12:27 kernel/

lrwxrwxrwx 1 root root 29 May 31 16:57 lib -> ../linux-headers-3.2.0-23/lib/

lrwxrwxrwx 1 root root 34 May 31 16:57 Makefile -> ../linux-headers-3.2.0-23/Makefile

-rw-r–r– 1 root root 608 Apr 11 2012 .missing-syscalls.d

lrwxrwxrwx 1 root root 28 May 31 16:57 mm -> ../linux-headers-3.2.0-23/mm/

-rw-r–r– 1 root root 0 Jul 2 11:21 modules.order

-rw-r–r– 1 root root 791023 Apr 11 2012 Module.symvers

lrwxrwxrwx 1 root root 29 May 31 16:57 net -> ../linux-headers-3.2.0-23/net/

lrwxrwxrwx 1 root root 33 May 31 16:57 samples -> ../linux-headers-3.2.0-23/samples/

drwxr-xr-x 7 root root 4096 Apr 25 2012 scripts/

lrwxrwxrwx 1 root root 34 May 31 16:57 security -> ../linux-headers-3.2.0-23/security/

lrwxrwxrwx 1 root root 31 May 31 16:57 sound -> ../linux-headers-3.2.0-23/sound/

lrwxrwxrwx 1 root root 25 May 31 16:57 source -> /build/buildd/linux-3.2.0

drwxr-xr-x 2 root root 4096 Apr 11 2012 .tmp_versions/

lrwxrwxrwx 1 root root 31 May 31 16:57 tools -> ../linux-headers-3.2.0-23/tools/

lrwxrwxrwx 1 root root 32 May 31 16:57 ubuntu -> ../linux-headers-3.2.0-23/ubuntu/

lrwxrwxrwx 1 root root 29 May 31 16:57 usr -> ../linux-headers-3.2.0-23/usr/

lrwxrwxrwx 1 root root 30 May 31 16:57 virt -> ../linux-headers-3.2.0-23/virt/

138 COMMENTS

montuviky February 3, 2012 At 4:29 PM

Away-some post will love to read all (and more :) )

- anil_pugalia January 24, 2013 At 12:30 PM
  
  Thanks for the appreciation. Go ahead & read all 24 are out in hard form.
  
vivek February 18, 2012 At 1:00 PM

when I run make command, i got the following error

make: Nothing to be done for `default’.

I guess it could be the problem because of KERNEL_SOURCE. In my make file i have set KERNEL_SOURCE as follows:

KERNEL_SOURCE := /usr/src/linux-headers-2.6.38-10

- the_summer May 4, 2012 At 12:24 AM
  
  I had the same problem.
  For me the problem was copy and pasting the Makefile.
  Make sure that in front of the ${MAKE}… commands is an tab and not multiple spaces.
  After replacing spaces with tabs it worked for me.
  
  - avik August 9, 2012 At 10:52 PM
    
    thanks for the solution
    
- the_summer May 4, 2012 At 12:32 AM
  
  Just noticed:
  I don’t know if you use *buntu. But KERNEL_SOURCE := /usr/src/linux-headers-2.6.38-10 produces some errors.
  
  KERNEL_SOURCE := /usr/src/linux-headers-2.6.38-10-generic seems to work.
  
  - Raghu November 19, 2012 At 11:02 AM
    
    # Use this file as your “Makefile”
    
    obj-m +=ofd.o
    
    ofd-objs := ofd.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
    
    - Raghu November 19, 2012 At 12:17 PM
      
      add #include in ofd.c and remove 2nd line from above
      Makefile and compile..
      
montuviky February 20, 2012 At 10:56 AM

I also had the same problem.

So i manually complied it.

make was like

obj-m := ofd.o

and compilation was :

make -C /usr/src/linux-headers-2.6.38-10 SUBDIRS=$PWD modules.

- Teja July 28, 2012 At 5:49 AM
  
  Thanx bro…
  
- akash December 4, 2012 At 10:08 PM
  
  hey frnd what does this modules word signify in above make command ….
  do we need to put module path replacing this or directly run above cmmnd as it is … reply pls
  
  - Anil Pugalia December 6, 2012 At 11:27 AM
    
    Its directly the above command as is.
    
Rakesh Babu February 25, 2012 At 10:01 PM

Rakesh babu
Dynamically load or unload a driver means…..

- Anil Pugalia July 10, 2012 At 11:51 AM
  
  Read the previous article https://www.opensourceforu.com/2010/11/understanding-linux-device-drivers/
  
Curious_Furious April 7, 2012 At 3:40 PM

Where should the C program be placed? In which directory?
In your Makefile, what will be the pwd?

- anil_pugalia November 28, 2012 At 8:31 PM
  
  In any folder of its own.
  
PeterHiggs August 20, 2012 At 10:51 AM

i liked it :) thanks pugs

- Anil Pugalia August 20, 2012 At 6:00 PM
  
  You are welcome
  
PeterHiggs August 20, 2012 At 10:58 AM

hi pugs, all is well. But I need to know a little more about the Makefile syntax and how it works line by line… I can’t digest some code which is alien to me. I would be grateful if you can throw some light on this….

- khamar September 7, 2012 At 4:22 PM
  
  wats answer to ur auestion?
  
- Anil Pugalia September 7, 2012 At 7:29 PM
  
  Try to read up “info make”
  
explorer November 14, 2012 At 3:54 PM

when ubuntu is installed on desktop

what does /usr/src/ dir contains ? i.e kerner source OR kernel headers?

in my pc linux-headers-2.6.38-10-generic and linux-headers-2.6.38-10 directories are there. what are they.? they dont have any c source . if they are headers why there are two directories i.e what is generic means?

- anil_pugalia November 28, 2012 At 8:34 PM
  
  They are headers. Sources can also be installed in the same folder using apt-get install linux-sources. Two headers are just the two variants created by the particular distro – ubuntu here
  
  - calixto November 29, 2012 At 11:40 AM
    
    its apt-get linux-source
    
    - calixto November 29, 2012 At 11:43 AM
      
      sorry apt-get install linux-source
      
      - anil_pugalia November 29, 2012 At 2:40 PM
        
        Thanks for the correction. I also corrected it.
akash December 2, 2012 At 10:19 PM

how to check kernel location …

- Anil Pugalia December 3, 2012 At 8:02 AM
  
  I understand you mean the kernel source location. Typically, it would be under /usr/src (linux or build or …). Also, it may not be installed by default. So, you may have to install it first.
  
akash December 4, 2012 At 9:56 PM

root@ubuntu:/usr/src# make -C /usr/src/linux-headers-3.2.0-29 SUBDIRS=$PWD modules.
I run above command & found this error pls help as soon as possible .. pls

make: Entering directory `/usr/src/linux-headers-3.2.0-29′

ERROR: Kernel configuration is invalid.
include/generated/autoconf.h or include/config/auto.conf are missing.
Run ‘make oldconfig && make prepare’ on kernel src to fix it.

- akash December 5, 2012 At 10:41 PM
  
  pls reply …m waiting
  
  - Anil Pugalia December 6, 2012 At 11:26 AM
    
    So, as it is mentioned in the above error, do make oldconfig after going into the linux-headers-3.2.0.29 folder.
    
akash December 9, 2012 At 12:16 AM

i was trying to build my driver …i got this error … :-

root@ubuntu:/home/ayush/device# make -C /usr/src/linux-headers-3.2.0-29-generic-pae SUBDIRS=$PWD modules

make: Entering directory `/usr/src/linux-headers-3.2.0-29-generic-pae’

Building modules, stage 2.

MODPOST 0 modules

make: Leaving directory `/usr/src/linux-headers-3.2.0-29-generic-pae’

Pls reply any solution … thnx in advance :)

- Anil Pugalia December 9, 2012 At 7:09 PM
  
  I believe you current directory /home/ayush/device contains the C files which you are trying to build. And your current kernel configuration is set to build & use drivers, i.e. “grep CONFIG_MODULE /usr/src/linux-headers-3.2.0-29-generic-pae/.config” should not be not set or empty.
  
  - janakiram March 20, 2013 At 11:06 PM
    
    I am also facing same problem as mentioned.. it’s showing
    
    CONFIG_MODULES=y
    # CONFIG_MODULE_FORCE_LOAD is not set
    CONFIG_MODULE_UNLOAD=y
    # CONFIG_MODULE_FORCE_UNLOAD is not set
    CONFIG_MODULE_SRCVERSION_ALL=y
    
    - Anil Pugalia March 21, 2013 At 6:22 PM
      
      Use a makefile as suggested in the article. Basically you need the obj-m … line for a module to be built, i.e. obj-m := ofd.o. So, just giving make on command line may not work.
      
satheesaran December 20, 2012 At 8:24 PM

Great example to start with. Thanks for the article :) Motivates to read more

- Anil Pugalia December 21, 2012 At 8:53 AM
  
  Those words are really inspiring for me.
  
yogesh January 20, 2013 At 3:15 PM

why every function in the device driver is named as static. As static fuction are not visible outside of the file scope. Then, How these driver function gets called by user space application..

- anil_pugalia January 24, 2013 At 12:34 PM
  
  You are correct that when static, functions are not visible outside of the file scope, but only by their names. Note that, they could be still accessed anywhere by their addresses, and that’s what we do with all these driver functions – populate their addresses into the struct file_operations and make it available to VFS & hence userspace, through the struct cdev.
  
manoj February 11, 2013 At 3:21 PM

device drivers and it’s sources of Linux

tushar February 20, 2013 At 10:07 PM

when i do make this error comes

please tell solution

sai@ubuntu:~/tushar$ make

make -C /usr/src/linux-headers-3.5.0-17 SUBDIRS=/home/sai/tushar modules

make[1]: Entering directory `/usr/src/linux-headers-3.5.0-17′

ERROR: Kernel configuration is invalid.

include/generated/autoconf.h or include/config/auto.conf are missing.

Run ‘make oldconfig && make prepare’ on kernel src to fix it.

WARNING: Symbol version dump /usr/src/linux-headers-3.5.0-17/Module.symvers

is missing;

modules will have no dependencies and modversions.

Building modules, stage 2.

/usr/src/linux-headers-3.5.0-17/scripts/Makefile.modpost:42:

include/config/auto.conf: No such file or directory

make[2]: *** No rule to make target `include/config/auto.conf’. Stop.

make[1]: *** [modules]

Error 2

make[1]: Leaving directory `/usr/src/linux-headers-3.5.0-17′

make: *** [default] Error 2

- tushar February 21, 2013 At 1:17 PM
  
  please reply i am waiting
  
  - Anil Pugalia February 22, 2013 At 4:02 PM
    
    Do as the message says: make oldconfig
    And then, make modules_prepare
    Both in the linux-headers folder.
    And then retry.
    
    - tushar February 22, 2013 At 5:57 PM
      
      1> when i do make oldconfig in linux-headers-3.5..0-17 folder i got this error
      
      HOSTCC scripts/basic/fixdep
      
      scripts/basic/fixdep.c:433:1: fatal error: opening dependency file scripts/basic/.fixdep.d: Permission denied
      
      compilation terminated.
      
      make[1]: *** [scripts/basic/fixdep] Error 1
      
      make: *** [scripts_basic] Error 2
      
      tushar@Sai:/usr/src/linux-headers-3.5.0-17$
      
      2> and after that if i do make modules_prepare i got this error
      
      HOSTCC scripts/basic/fixdep
      
      scripts/basic/fixdep.c:433:1: fatal error: opening dependency file scripts/basic/.fixdep.d: Permission denied
      
      compilation terminated.
      
      make[2]: *** [scripts/basic/fixdep] Error 1
      
      make[1]: *** [scripts_basic] Error 2
      
      make: *** No rule to make target `modules_prepare’. Stop.
      
      tushar@Sai:/usr/src/linux-headers-3.5.0-17$
      
      i am using ubuntu 12.10
      kernel version 3.5.0-17-generic
      
      PLZ PROVIDE SOLUTION SIR
      
      - tushar February 23, 2013 At 2:23 PM
        
        plz reply
      - Anil Pugalia February 25, 2013 At 3:41 PM
        
        Use sudo, yaar.
        sudo make oldconfig
      - tushar February 25, 2013 At 5:36 PM
        
        1)when i do sudo make oldconfig then it is fine
        
        2) but when i do sudo make modules_prepare i got fooliowing error
        
        tushar@Sai:/usr/src/linux-headers-3.5.0-17$ sudo make modules_prepare
        
        scripts/kconfig/conf –silentoldconfig Kconfig
        
        make[1]: *** No rule to make target `/usr/src/linux-headers-3.5.0-17/arch/x86/syscalls/syscall_32.tbl’, needed by `arch/x86/syscalls/../include/generated/asm/unistd_32.h’. Stop.
        
        make: *** [archheaders] Error 2
        
        tushar@Sai:/usr/src/linux-headers-3.5.0-17$
        
        pls tell solution sir
      - Anil Pugalia February 25, 2013 At 7:46 PM
        
        How about sudo make prepare?
        If not, then some issue with the headers package installation.
      - Sunil S June 30, 2013 At 12:53 AM
        
        hi.. i am facing the same problem Tushar was facing and got exact same error. I desperately want to move forward to next tutorial but can get rid of this compile issue…
        
        I know u said about headers package. But can you please point out exact issue..
        
        Here is my system info:
        
        Linux sunilshahu 3.5.0-17-generic #28-Ubuntu SMP Tue Oct 9 19:32:08 UTC 2012 i686 athlon i686 GNU/Linux
        
        and after doing what you suggested here is the error log i got:
        
        root@sunilshahu:/usr/src/linux-headers-3.5.0-17# make oldconfig
        HOSTCC scripts/basic/fixdep
        HOSTCC scripts/kconfig/conf.o
        SHIPPED scripts/kconfig/zconf.tab.c
        SHIPPED scripts/kconfig/zconf.lex.c
        SHIPPED scripts/kconfig/zconf.hash.c
        HOSTCC scripts/kconfig/zconf.tab.o
        HOSTLD scripts/kconfig/conf
        scripts/kconfig/conf –oldconfig Kconfig
        #
        # using defaults found in /boot/config-3.5.0-17-generic
        #
        #
        # configuration written to .config
        #
        root@sunilshahu:/usr/src/linux-headers-3.5.0-17#
        root@sunilshahu:/usr/src/linux-headers-3.5.0-17#
        root@sunilshahu:/usr/src/linux-headers-3.5.0-17# make prepare
        scripts/kconfig/conf –silentoldconfig Kconfig
        make[1]: *** No rule to make target `/usr/src/linux-headers-3.5.0-17/arch/x86/syscalls/syscall_32.tbl’, needed by `arch/x86/syscalls/../include/generated/asm/unistd_32.h’. Stop.
        make: *** [archheaders] Error 2
        root@sunilshahu:/usr/src/linux-headers-3.5.0-17# make prepare
        make[1]: *** No rule to make target `/usr/src/linux-headers-3.5.0-17/arch/x86/syscalls/syscall_32.tbl’, needed by `arch/x86/syscalls/../include/generated/asm/unistd_32.h’. Stop.
        make: *** [archheaders] Error 2
        
        Thanks…(it will we while(1){thanks;} if anybody will help to sort this out)
        
        Sunil.
      - anil_pugalia June 30, 2013 At 11:01 AM
        
        Does make modules_prepare also give the same problem? If yes, then as I said earlier, you also have the some issue with the headers package installation. Try reinstalling the linux-headers package using apt-get.
      - Sunil S June 30, 2013 At 1:17 PM
        
        ok. I did what Ajey said int the above discussion and changed make file as below
        
        KERNEL_SOURCE := /lib/modules/3.5.0-17-generic/build
        
        And it worked.. It compiled the ofd.c and i loaded and unloaded it successfully on my ubuntu 12.10.
        
        So, does it means my linux sources or headers are at above directory and not at /usr/src/linux-headers-3.5.0-17-generic and /usr/src/linux-source-3.5.0 , because i tried both earlier?
      - anil_pugalia June 30, 2013 At 2:41 PM
        
        Typically /lib/modules/…/build is a link to the corresponding source, these modules are built from – making it work with high probability. Please check the link and post here what does it point to. That would definitely give insight into this common problem.
      - Sunil S July 2, 2013 At 3:07 PM
        
        hi, i have to change the system after above comment and missed to see the link on that system.
        
        now i am using
        Linux sunils 3.2.0-23-generic #36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
        
        my code compiled with this with make file
        obj-m += ofd.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
        
        and when looking at the lib/modules/…/buld i find as below. but source link (/build/buildd/linux-3.2.0) was red colored(dont know why) and when looking what it points to i found that there is no such directory(but still i got my module compiled)
        
        total 1088
        
        drwxr-xr-x 7 root root 4096 Jul 2 13:54 ./
        
        drwxr-xr-x 5 root root 4096 Jun 26 16:05 ../
        
        drwxr-xr-x 3 root root 4096 Apr 25 2012 arch/
        
        lrwxrwxrwx 1 root root 31 May 31 16:57 block -> ../linux-headers-3.2.0-23/block/
        
        -rw-r–r– 1 root root 140241 Jul 2 13:53 .config
        
        -rw-r–r– 1 root root 140241 Jul 2 12:25 .config.old
        
        lrwxrwxrwx 1 root root 32 May 31 16:57 crypto -> ../linux-headers-3.2.0-23/crypto/
        
        lrwxrwxrwx 1 root root 39 May 31 16:57 Documentation -> ../linux-headers-3.2.0-23/Documentation/
        
        lrwxrwxrwx 1 root root 33 May 31 16:57 drivers -> ../linux-headers-3.2.0-23/drivers/
        
        lrwxrwxrwx 1 root root 34 May 31 16:57 firmware -> ../linux-headers-3.2.0-23/firmware/
        
        lrwxrwxrwx 1 root root 28 May 31 16:57 fs -> ../linux-headers-3.2.0-23/fs/
        
        drwxr-xr-x 5 root root 4096 Apr 25 2012 include/
        
        lrwxrwxrwx 1 root root 30 May 31 16:57 init -> ../linux-headers-3.2.0-23/init/
        
        lrwxrwxrwx 1 root root 29 May 31 16:57 ipc -> ../linux-headers-3.2.0-23/ipc/
        
        lrwxrwxrwx 1 root root 32 May 31 16:57 Kbuild -> ../linux-headers-3.2.0-23/Kbuild
        
        lrwxrwxrwx 1 root root 33 May 31 16:57 Kconfig -> ../linux-headers-3.2.0-23/Kconfig
        
        drwxr-xr-x 2 root root 4096 Jul 2 12:27 kernel/
        
        lrwxrwxrwx 1 root root 29 May 31 16:57 lib -> ../linux-headers-3.2.0-23/lib/
        
        lrwxrwxrwx 1 root root 34 May 31 16:57 Makefile -> ../linux-headers-3.2.0-23/Makefile
        
        -rw-r–r– 1 root root 608 Apr 11 2012 .missing-syscalls.d
        
        lrwxrwxrwx 1 root root 28 May 31 16:57 mm -> ../linux-headers-3.2.0-23/mm/
        
        -rw-r–r– 1 root root 0 Jul 2 11:21 modules.order
        
        -rw-r–r– 1 root root 791023 Apr 11 2012 Module.symvers
        
        lrwxrwxrwx 1 root root 29 May 31 16:57 net -> ../linux-headers-3.2.0-23/net/
        
        lrwxrwxrwx 1 root root 33 May 31 16:57 samples -> ../linux-headers-3.2.0-23/samples/
        
        drwxr-xr-x 7 root root 4096 Apr 25 2012 scripts/
        
        lrwxrwxrwx 1 root root 34 May 31 16:57 security -> ../linux-headers-3.2.0-23/security/
        
        lrwxrwxrwx 1 root root 31 May 31 16:57 sound -> ../linux-headers-3.2.0-23/sound/
        
        lrwxrwxrwx 1 root root 25 May 31 16:57 source -> /build/buildd/linux-3.2.0
        
        drwxr-xr-x 2 root root 4096 Apr 11 2012 .tmp_versions/
        
        lrwxrwxrwx 1 root root 31 May 31 16:57 tools -> ../linux-headers-3.2.0-23/tools/
        
        lrwxrwxrwx 1 root root 32 May 31 16:57 ubuntu -> ../linux-headers-3.2.0-23/ubuntu/
        
        lrwxrwxrwx 1 root root 29 May 31 16:57 usr -> ../linux-headers-3.2.0-23/usr/
        
        lrwxrwxrwx 1 root root 30 May 31 16:57 virt -> ../linux-headers-3.2.0-23/virt/
      - anil_pugalia July 2, 2013 At 4:57 PM
        
        What output have you sent? Please send the output of:
        ls -l /lib/modules/`uname -r`/
      - Sunil S July 12, 2013 At 4:12 PM
        
        Here is the output:
        
        root@sunils:~# ls -l /lib/modules/`uname -r`/
        
        total 4276
        
        lrwxrwxrwx 1 root root 39 May 31 16:56 build -> /usr/src/linux-headers-3.2.0-23-generic
        
        drwxr-xr-x 2 root root 4096 Apr 25 2012 initrd
        
        drwxr-xr-x 10 root root 4096 Apr 25 2012 kernel
        
        -rw-r–r– 1 root root 685840 Apr 25 2012 modules.alias
        
        -rw-r–r– 1 root root 667167 Apr 25 2012 modules.alias.bin
        
        -rw-r–r– 1 root root 5724 Apr 11 2012 modules.builtin
        
        -rw-r–r– 1 root root 7132 Apr 25 2012 modules.builtin.bin
        
        -rw-r–r– 1 root root 69 Apr 25 2012 modules.ccwmap
        
        -rw-r–r– 1 root root 314947 Apr 25 2012 modules.dep
        
        -rw-r–r– 1 root root 463653 Apr 25 2012 modules.dep.bin
        
        -rw-r–r– 1 root root 186 Apr 25 2012 modules.devname
        
        -rw-r–r– 1 root root 889 Apr 25 2012 modules.ieee1394map
        
        -rw-r–r– 1 root root 295 Apr 25 2012 modules.inputmap
        
        -rw-r–r– 1 root root 4624 Apr 25 2012 modules.isapnpmap
        
        -rw-r–r– 1 root root 1421 Apr 25 2012 modules.ofmap
        
        -rw-r–r– 1 root root 128682 Apr 11 2012 modules.order
        
        -rw-r–r– 1 root root 451186 Apr 25 2012 modules.pcimap
        
        -rw-r–r– 1 root root 2815 Apr 25 2012 modules.seriomap
        
        -rw-r–r– 1 root root 131 Apr 25 2012 modules.softdep
        
        -rw-r–r– 1 root root 260900 Apr 25 2012 modules.symbols
        
        -rw-r–r– 1 root root 330555 Apr 25 2012 modules.symbols.bin
        
        -rw-r–r– 1 root root 998947 Apr 25 2012 modules.usbmap
      - anil_pugalia July 13, 2013 At 9:59 AM
        
        I hope that clarifies all the doubts. The link is correctly pointing to the headers, which are working for you. Pasting it here for reference:
        lrwxrwxrwx 1 root root 39 May 31 16:56 build -> /usr/src/linux-headers-3.2.0-23-generic
darcy.diao@gmail.com February 28, 2013 At 5:19 PM

I use your code and compile successfully.
But when insmod by “sudo insmod ofd.ko”, error prompt-” insmod: error inserting ‘ofd.ko’: -1 Invalid module format”.
Can you tell me why?
Thx.

- Anil Pugalia February 28, 2013 At 6:56 PM
  
  Make sure that the kernel headers you used to compile the driver has the same version as the running kernel.
  
- darcy.diao@gmail.com March 1, 2013 At 6:54 AM
  
  I change the KERNEL_SOURCE to /lib/module/$(shell uname -r)/build.
  It is ok right now.
  
tushraj March 6, 2013 At 2:14 PM

I use your code and compile by make command then i got following error

tushar@tushar-SVE14112ENW:~/devdrv$ make
make -C /usr/src/linux-headers-3.5.0-17 SUBDIRS=/home/tushar/devdrv modules
make[1]: Entering directory `/usr/src/linux-headers-3.5.0-17′
WARNING: Symbol version dump /usr/src/linux-headers-3.5.0-17/Module.symvers is missing;
modules will have no dependencies and modversions.
Building modules, stage 2.

MODPOST 0 modules

/bin/sh: 1: scripts/mod/modpost: not found

make[2]: *** [__modpost] Error 127

make[1]: *** [modules] Error 2

make[1]: Leaving directory `/usr/src/linux-headers-3.5.0-17′

make: *** [default] Error 2

- Anil Pugalia March 6, 2013 At 3:17 PM
  
  Check out the comments below for the solution to the same problem.
  
enigma March 10, 2013 At 7:59 PM

obj-m := ofd.o should be obj-m += ofd.o ?

- Anil Pugalia March 11, 2013 At 12:14 PM
  
  In this particular case, even := is fine as, we are limiting the build to the drivers directory and more to our driver, alone.
  
janakiram March 18, 2013 At 3:08 PM

I use your code and compile by make command then i got following errors

make -C /usr/src/linux-headers-3.2.0-29 SUBDIRS=/home/shivaram/jani modules
make[1]: Entering directory `/usr/src/linux-headers-3.2.0-29′

ERROR: Kernel configuration is invalid.
include/generated/autoconf.h or include/config/auto.conf are missing.
Run ‘make oldconfig && make prepare’ on kernel src to fix it.

WARNING: Symbol version dump /usr/src/linux-headers-3.2.0-29/Module.symvers
is missing; modules will have no dependencies and modversions.

Building modules, stage 2.
/usr/src/linux-headers-3.2.0-29/scripts/Makefile.modpost:42: include/config/auto.conf: No such file or directory
make[2]: *** No rule to make target `include/config/auto.conf’. Stop.
make[1]: *** [modules] Error 2
make[1]: Leaving directory `/usr/src/linux-headers-3.2.0-29′
make: *** [default] Error 2s

And also i tried with make oldconfig&&make prepare then i got problem like

make: *** No rule to make target `oldconfig’. Stop.

i installed ubuntu through vmware. one of my friend said it’s the problem u should install normal way..

- Anil Pugalia March 19, 2013 At 12:25 PM
  
  Check out the discussion threads below.
  
uday March 19, 2013 At 10:02 PM

sir,i have created a makefile and added obj-m := ofd.o in it.

After saving and exiting the terminal,i have given command like this

make -C /usr/src/linux-headers-generic-pae-3.2.0-12 SUBDIRS=$PWD modules

but it is showing “no rule to make”…pls help me.
regards,
uday.

- Anil Pugalia March 20, 2013 At 9:24 AM
  
  Make sure that you use *only tabs* to indent your makefile. You get such errors, if you have used spaces instead.
  
Ajey June 2, 2013 At 1:12 PM

Namaste, When I used Kernel_Source as KERNEL_SOURCE := /usr/src/linux-header-3.5.0-30-generic –> I get an error No such file or directory and when I change Kernel_Source as KERNEL_SOURCE := /lib/modules/3.5.0-30-generic/build (this was recommended in one of comments below), then I get following error. Not able to proceed beyond this ….

make -C /lib/modules/3.5.0-30-generic/build SUBDIRS=/ modules
make[1]: Entering directory `/usr/src/linux-headers-3.5.0-30-generic’
scripts/Makefile.build:128: kbuild: Makefile.build is included improperly
make[2]: *** No rule to make target `kernel/bounds.c’, needed by `kernel/bounds.s’. Stop.
make[1]: *** [_module_] Error 2
make[1]: Leaving directory `/usr/src/linux-headers-3.5.0-30-generic’
make: *** [default] Error 2

- anil_pugalia June 7, 2013 At 8:19 PM
  
  Seems like, there is some problem with the installation of the kernel headers with this version of the distro you are using.
  
- xpress_embedo November 10, 2013 At 12:00 PM
  
  I too got this error, the problem was that I had created a folder Linux Device Driver and under this HelloWorld, When i remove Space and Change Folder name as LinuxDeviceDriver, everything works fine, Hoping you too had done same thing.
  Hope this help.
  
  Very Nice Tutorial:-)
  
  - anil_pugalia November 11, 2013 At 7:44 PM
    
    Oh! That’s great input. Hey guys, please fix your problems, if you are having the same problem.
    
Ajey June 4, 2013 At 7:48 PM

After I upgraded to Ubuntu 13.04, the problem got rectified, only thing is, in the sample Makefile, I had to change Kernel_Source := /lib/modules//3.8.0-23-generic/build. Thanks for this article.

- anil_pugalia June 7, 2013 At 8:17 PM
  
  You are welcome.
  
nandan August 1, 2013 At 9:53 PM

Thanks sir ..you have done a great job.

- anil_pugalia August 3, 2013 At 10:35 AM
  
  Thanks for reading & appreciating.
  
nbtsos August 10, 2013 At 3:04 PM

hi sir, i can compile on ubuntu version 8, but when i use ubuntu 12.04 lts, i tried every way to compile but still cannot compile:
user@ubuntu:~/Study$ make
make: Nothing to be done for `default’.

Then i add “default: ofd.o” to our Makefile but it raise another error:
cc -c -o ofd.o ofd.c
ofd.c:2:26: fatal error: linux/module.h: No such file or directory compilation terminated.

Later, i must use command (type manually to terminal) like this to compile :
make -C /lib/modules/3.5.0-37-generic/build SUBDIRS=/home/user/Study modules

And the result is OK:
make: Entering directory `/usr/src/linux-headers-3.5.0-37-generic’
CC [M] /home/nobita/Study/ofd.o
Building modules, stage 2.
MODPOST 1 modules
CC /home/nobita/Study/ofd.mod.o
LD [M] /home/nobita/Study/ofd.ko
make: Leaving directory `/usr/src/linux-headers-3.5.0-37-generic’

Could you help me how to handle this, and why cant i use Makefile??
Thanks in advance!

- nbtsos August 10, 2013 At 4:25 PM
  
  And there is a slight problem here, when using Ubuntu 8.x (kernel 2.6x) with your Makefile, everything ok. When insmod -> dmesg -> get line “Namaskar: ofcd registered”, when rmmod -> dmesg -> get line “Alvida: ofcd unregistered”. But with ubuntu 12.04 LTS (kernel 3.5x), compile with method state above, when When insmod -> dmesg -> nothing, but when rmmod -> dmesg -> get 2 line “Namaskar… and Alvida…” <= confuse?? line Namaskar must be appear after insmod, right?
  
  When trying you example in part 5 (still compile like above), everything's gone smoothly apart from when dmesg, all line involve in open, close … appear correctly but still 2 line "Namaskar… and Alvida…" appear only when i rmmod. I dont know why, the code is exactly the same like you.
  
  Another problem: with example in part 5, when using Ubuntu 8.x (actually i use virtual machine to run this OS), compile ok, but when insmod got error: Segmentation fault, …. address 0x00000…., i tried to debug it (still not familiar with it) and i figured problem involving in device_create, so i cant get mynull. But with Ubuntu 12 (installed in my laptop by wubi) everything work well except the problem about message line i mentioned before.
  
  - anil_pugalia August 15, 2013 At 4:41 AM
    
    Hardware access through virtual box is not recommended and you have the segfault kind of issues, as mentioned by you.
    
    Regarding the dmesg output, its a delayed buffer flush issue. Put a “n” at the end of each of the strings, and things should work fine.
    
- anil_pugalia August 15, 2013 At 4:38 AM
  
  Change the KERNEL_SOURCE variable in the Makefile to /lib/modules/3.5.0-37-generic/build and you should be able to use your Makefile – it just that the kernel source path is different on your system.
  
why bother September 27, 2013 At 9:37 PM

Thank you very much for this simple example! Comment section helped a lot too! Great to be doing Linux device drivers!

- anil_pugalia September 30, 2013 At 10:00 PM
  
  Thanks for your appreciation, as well.
  
Ajay December 10, 2013 At 4:31 PM

Hi sir,
I am getting there error plz help me out

ajay@ubuntu:~/module$ make
make -C /usr/src/linux-headers-3.5.0-17-generic SUBDIRS-/home/ajay/module module
make[1]: Entering directory `/usr/src/linux-headers-3.5.0-17-generic’
HOSTCC scripts/basic/fixdep
scripts/basic/fixdep.c:433:1: fatal error: opening dependency file scripts/basic/.fixdep.d: Permission denied
compilation terminated.
make[3]: *** [scripts/basic/fixdep] Error 1
make[2]: *** [scripts_basic] Error 2
make[1]: *** No rule to make target `SUBDIRS-/home/ajay/module’. Stop.
make[1]: Leaving directory `/usr/src/linux-headers-3.5.0-17-generic’
make: *** [all] Error 2

Ajay December 10, 2013 At 4:31 PM

Hi sir,
I am getting there error plz help me out

ajay@ubuntu:~/module$ make
make -C /usr/src/linux-headers-3.5.0-17-generic SUBDIRS-/home/ajay/module module
make[1]: Entering directory `/usr/src/linux-headers-3.5.0-17-generic’
HOSTCC scripts/basic/fixdep
scripts/basic/fixdep.c:433:1: fatal error: opening dependency file scripts/basic/.fixdep.d: Permission denied
compilation terminated.
make[3]: *** [scripts/basic/fixdep] Error 1
make[2]: *** [scripts_basic] Error 2
make[1]: *** No rule to make target `SUBDIRS-/home/ajay/module’. Stop.
make[1]: Leaving directory `/usr/src/linux-headers-3.5.0-17-generic’
make: *** [all] Error 2

- anil_pugalia December 16, 2013 At 9:44 PM
  
  I hope pjm’s comment as mentioned above, has solved your problem.
  
pjmpjm December 11, 2013 At 9:10 AM

peter@Ubuntu2:~$
peter@Ubuntu2:~$ rm ofd.mod.o
peter@Ubuntu2:~$ rm ofd.ko
peter@Ubuntu2:~$
peter@Ubuntu2:~$ make -f makefile
make: Nothing to be done for `default’.
peter@Ubuntu2:~$ make -f Makefile
make -C /usr/src/linux-headers-3.2.0-56-generic SUBDIRS=/home/peter modules
make[1]: Entering directory `/usr/src/linux-headers-3.2.0-56-generic’
Building modules, stage 2.
MODPOST 1 modules
CC /home/peter/ofd.mod.o
LD [M] /home/peter/ofd.ko
make[1]: Leaving directory `/usr/src/linux-headers-3.2.0-56-generic’
peter@Ubuntu2:~$

makefile( indented lines have 4 leading spaces – using cut&paste from this article)

ifneq (${KERNELRELEASE},)
obj-m := ofd.o
# Otherwise we were called directly from the command line.
# Invoke the kernel build system.
else
KERNEL_SOURCE := /usr/src/linux-headers-3.2.0-56-generic
PWD := $(shell pwd)
default:
${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} modules

clean:
${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} clean
endif

Makefile ( indented lines have 1 leading tab after editing)

ifneq (${KERNELRELEASE},)
obj-m := ofd.o
# Otherwise we were called directly from the command line.
# Invoke the kernel build system.
else
KERNEL_SOURCE := /usr/src/linux-headers-3.2.0-56-generic
PWD := $(shell pwd)
default:
${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} modules

clean:
${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} clean
endif

Sooooooo … if you cut and paste from this tutorial to create your makefile edit it so that the leading white space is one Tab – this is with Ububtu 12.04

hope this helps

nice work Anil

pjm

- anil_pugalia December 16, 2013 At 9:42 PM
  
  Thanks pjm.
  
Sham December 20, 2013 At 5:30 PM

Hello,

I am trying to compile USB driver code, but getting following
warnings:

root@ubuntu:/opt/linux-cortexm-1.4.1/projects/developer/app/driver#
make
make -C /opt/linux-cortexm-1.4.1/linux M=`pwd` modules CFLAGS=””
LDFLAGS=””
make[1]: Entering directory `/opt/linux-cortexm-1.4.1/linux’
CC [M] /opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.o
Building modules, stage 2.
MODPOST 1 modules
WARNING: “usb_register_driver”
[/opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.ko]
undefined!
WARNING: “usb_register_dev”
[/opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.ko]
undefined!
WARNING: “usb_get_dev”
[/opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.ko]
undefined!
WARNING: “usb_put_dev”
[/opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.ko]
undefined!
WARNING: “usb_deregister_dev”
[/opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.ko]
undefined!
WARNING: “usb_find_interface”
[/opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.ko]
undefined!
WARNING: “usb_bulk_msg”
[/opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.ko]
undefined!
WARNING: “usb_deregister”
[/opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.ko]
undefined!
CC /opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.mod.o
LD [M]
/opt/linux-cortexm-1.4.1/projects/developer/app/driver/vcom.ko
make[1]: Leaving directory `/opt/linux-cortexm-1.4.1/linux’

I searched all these functions, these are defind in following files.

1> usb_register_driver -> Defined /usb/core/driver.c, line 824.
2> usb_register_dev -> Defined /usb/core/file.c, line 160
3> usb_get_dev -> Defined /usb/core/usb.c, line 492
4> usb_put_dev -> Defined /usb/core/usb.c, line 518
5> usb_deregister_dev -> Defined /usb/core/usb.c, line 240
6> usb_find_interface -> Defined /usb/core/usb.c, line 198

It is clear from above these functions are defined somewhere.

Let us know how to solve it.

- anil_pugalia December 30, 2013 At 10:35 PM
  
  Why did you set the CFLAGS & LDFLAGS to “” in your Makefile? Please remove both the CFLAGS & LDFLAGS in make invocation, and try out.
  
Sham December 20, 2013 At 5:32 PM

Hello,
I have already created .ko file and i have inserted to target using insmod and led is blinking but
I want to build driver into the kernel image(not as a module). First,
I have selected a /misc directory in drivers directory
.drivers/misc/I
have copied ledblink.c and lpc178x.h files into this directory and in
Kconfig present indrivers/misc/ directory, I have wriitten.

config LEDDRIVER
bool “led blink”
default n
help
This is a test driver.

Save the file and open Makefile in the same directory. Goto end of
the file and add the following entry.

obj-$(CONFIG_LEDDRIVER) += ledblink.o

make kmenuconfig and I have selected led blink

But make command gives following error:
LD drivers/media/built-in.o
LD drivers/mfd/built-in.o
make[3]: *** No rule to make target `drivers/misc/ledblink.o’, needed
by `drivers/misc/built-in.o’. Stop.
make[2]: *** [drivers/misc] Error 2
make[1]: *** [drivers] Error 2
make[1]: Leaving directory `/opt/linux-cortexm-1.4.1/linux’
make: *** [_prepare_modules] Error 2
Please let me know what is missing.

- anil_pugalia December 30, 2013 At 10:46 PM
  
  What you are doing is correct. Check out your Makefile, if something else is needed. Also, try make modules_prepare, before make.
  
Akshay March 19, 2014 At 12:01 AM

Hi,
I have just installed linux on VM.
When I do “make” it shows the following error:
make[1]: *** No rule to make target `/usr/src/linux-headers-3.8.0-29-generic/arch/x86/syscalls/syscall_32.tbl’, needed by `arch/x86/syscalls/../include/generated/uapi/asm/unistd_32.h’. Stop.
make: *** [archheaders] Error 2

- anil_pugalia March 19, 2014 At 6:52 PM
  
  Seems like kernel headers are not installed (properly).
  
  - Akshay March 19, 2014 At 7:44 PM
    
    I think I’ve installed whatever is needed. ‘Cause whenever I try to install the headers, it says “nothing upgraded”. Is that the only cause to this?
    
    - anil_pugalia March 21, 2014 At 3:11 PM
      
      Okay, where exactly are you doing make. Also, make sure that your Makefile as appropriate tabs, not spaces – Makefiles are very tab sensitive.
      
ankit.singhal85@yahoo.com May 29, 2014 At 12:04 PM

what is KERNELRELEASE in the Makefile……?? someone told me that it’s the kernel version, which we are using !!! is it so???……if it’s so, then why we are not using the `uname -r` instead of this….!!!

- anil_pugalia June 12, 2014 At 12:30 PM
  
  This is the makefile variable defined in the kernel source, which defines the kernel release version for that particular kernel source, which need not have any relation with the running kernel.
  
ankit.singhal85@yahoo.com June 5, 2014 At 10:16 AM

@anil sir…..what’s the meaning of API??? like spinlock API, semaphore API, completion API in device drivers????

- anil_pugalia June 12, 2014 At 12:31 PM
  
  API as such stands for “Application Programming Interface”, but in our context, it means the set of functions provided by kernel for programming the particular functionalities.
  
Aravind July 4, 2014 At 11:51 PM

Dear Sir,,,Can you please explain driver code for interfacing a RapidIO?

- anil_pugalia July 31, 2014 At 11:09 AM
  
  That’s a very generic request. Please specify what do you want to achieve with that driver.
  
  - Aravind August 3, 2014 At 11:10 PM
    
    @anil sir,,I want to interface a RapidIO driver with a T4240 processor. I have setup the host system in Ubuntu 12.04 and initially I want to test the mport(master port) driver so that I can gradually create the rapidio interface.
    Kindly offer some suggestions.
    
    - anil_pugalia August 4, 2014 At 4:36 PM
      
      Is RapidIO interface more like a network interface? If yes, you may write a network (vertical) driver, or otherwise you may start with writing a character (vertical) driver.
      
      - Aravind August 4, 2014 At 5:29 PM
        
        Rapidio is a chip to chip or board to board interface. Also the driver was already implemented in 2005 but I want to know if it is compatible with T4240.
        If so what are steps to integrate with Ubuntu 12.04. If no then where I can go for a suitable rapdio driver.
        Kindly provide some suggestions.
        Thanks.
      - anil_pugalia August 5, 2014 At 5:59 PM
        
        Okay. So then for compatibility, just load the driver and check out. Or, it is not part of the distro, download the source and compile for it, and then try out.
      - Aravind August 7, 2014 At 4:36 PM
        
        Thank you sir.
        I will try.
tahi August 27, 2014 At 5:15 PM

Hi there,
I am linux beginner. I install debian in virtualbox
I saw several directories /usr/src/

#KERNEL_SOURCE := /usr/src/linux-headers-3.2.0-4-686-pae
#KERNEL_SOURCE := /usr/src/linux-headers-3.2.0-4-common
#KERNEL_SOURCE := /usr/src/virtualbox-guest-4.1.18
# KERNEL_SOURCE := /usr/src/linux-kbuild-3.2

I not sure what is kernel source? I try to make all of them. But i got :
make: Nothing to be done for `default’.
What’s going on here? Please give me any idea

Thank you!

- anil_pugalia August 27, 2014 At 5:24 PM
  
  Typically, most of them are kernel headers and not kernel source and hence there wouldn’t be anything to build.
  
  - tahi August 28, 2014 At 7:34 AM
    
    thank you. How can i find out kernel source location?
    
    - anil_pugalia August 28, 2014 At 10:27 AM
      
      Okay. So, now you are building the drivers, and not the kernel – that can be done using the headers. And I think, that’s what you have resolved. But then, you need to make sure that you use the headers corresponding to your running kernel version. Check that using uname -r
      
      - tahi August 28, 2014 At 12:49 PM
        
        uname –all Linux debian-vir1 3.2.0-4-486 #1 Debian 3.2.60-1+deb7u3 i686 GNU/Linux
        
        i typed dmesg
        ofd: disagrees about version of symbol module_layout
        
        modinfo
        vermagic: 3.2.0-4-686-pae SMP mod_unload modversions 686
        
        In “/lib/module/”. we had 2 directories
        – 3.2.0-4-686-pae
        – 3.2.0-4-486
        
        I saw that some differences from version. But, i can not find out “build” folder in /lib/modules/3.2.0-4-486
        
        what’s going on here?I missed something?
      - anil_pugalia August 28, 2014 At 4:58 PM
        
        It may not have the build folder, but still the other stuff at the top level may be there. Just give the top folder itself as the path.
      - tahi August 28, 2014 At 5:34 PM
        
        Went to root folder and typed
        find -name -build
        this result:
        ./lib/modules/3.2.0-4-686-pae/build
        …
        may be, i missed “build” directory. How can i recover it?
        or maybe, when i install OS to virtual box. It’s difference with real machine?
      - tahi August 29, 2014 At 9:55 AM
        
        Hi there
        
        I fixed it.
        
        1. Download kernel soucre code from debina website
        http://security.debian.org/debian-security/pool/updates/main/l/linux/linux-headers-3.2.0-4-486_3.2.60-1+deb7u3_i386.deb
        
        2. Extract downloaded file. Then
        – Copy “build” and “source” to /lib/modules/3.2.0-4-486
        – copy “usr/src/linux-headers-3.2.0-4-486” to “/usr/src/”
        3. Edit Makefile
        KERNEL_SOURCE := /lib/modules/3.2.0-4-486/build
        4. Check modinfo and re insmod
        
        Thank for all,
        Sincerely,
        Tahi
      - anil_pugalia August 30, 2014 At 11:52 AM
        
        Great about your fixing the stuff.
        
        About testing, it depends on what functionality your driver provides, and how does it provide.
Vijay Kanta October 2, 2014 At 6:57 PM

Wonderful startup tutorial for junior linux programmers. However had to search around to actually link the /lib/modules… to the KERNEL_SOURCE, and I also had to substitute M= instead of SUBDIRS=

- anil_pugalia October 7, 2014 At 5:17 PM
  
  May be follow the more upto date versions from my blog at SysPlay: http://sysplay.in/blog
  Specifically, the above article is updated at: http://sysplay.in/blog/linux-device-drivers/2013/03/writing-your-first-linux-driver-in-the-classroom/
  
  - Vijay Kanta October 29, 2014 At 5:07 PM
    
    These are much better. Thanks.
    
    - anil_pugalia October 30, 2014 At 2:44 PM
      
      Welcome.
      
paras gupta October 17, 2014 At 2:10 PM

hi there,
under my /usr/src directory there are three directories

linux-headers-3.13.0-24
linux-headers-3.13.0-24-generic
virtualbox-guest-4.3.10

i tried using first two as linux headers but output is

make: Entering directory `/usr/src/linux-headers-3.13.0-24′

ERROR: Kernel configuration is invalid.
include/generated/autoconf.h or include/config/auto.conf are missing.
Run ‘make oldconfig && make prepare’ on kernel src to fix it.

mkdir: cannot create directory ‘…’: Permission denied

WARNING: Symbol version dump /usr/src/linux-headers-3.13.0-24/Module.symvers
is missing; modules will have no dependencies and modversions.

scripts/Makefile.build:44: /usr/src/linux-headers-3.13.0-24/…/Makefile: No such file or directory
make[1]: *** No rule to make target `/usr/src/linux-headers-3.13.0-24/…/Makefile’. Stop.
make: *** [_module_…] Error 2
make: Leaving directory `/usr/src/linux-headers-3.13.0-24′

so, what’s going on here? plz help me.

- anil_pugalia October 17, 2014 At 7:57 PM
  
  Which distro is it? Before try those paths, go into those folders and do the following steps:
  make oldconfig
  make modules_prepare
  
  - paras gupta October 18, 2014 At 10:04 PM
    
    it’s linux mint.
    and these commands are not working
    
    output is—
    HOSTCC scripts/basic/fixdep
    scripts/basic/fixdep.c:462:1: fatal error: opening dependency file scripts/basic/.fixdep.d: Permission denied
    }
    ^
    compilation terminated.
    make[2]: *** [scripts/basic/fixdep] Error 1
    make[1]: *** [scripts_basic] Error 2
    make: *** No rule to make target `modules_prepare’. Stop.
    
    - anil_pugalia October 19, 2014 At 6:08 PM
      
      You need to try them as root.
      
      - paras gupta November 5, 2014 At 11:29 PM
        
        sudo make oldconfig outputs:
        HOSTCC scripts/basic/fixdep
        HOSTCC scripts/kconfig/conf.o
        HOSTCC scripts/kconfig/zconf.tab.o
        HOSTLD scripts/kconfig/conf
        scripts/kconfig/conf –oldconfig Kconfig
        #
        # configuration written to .config
        #
        
        but sudo make modules_prepare outputs:
        make[1]: *** No rule to make target `/usr/src/linux-headers-3.13.0-24-generic/arch/x86/syscalls/syscall_32.tbl’, needed by `arch/x86/syscalls/../include/generated/uapi/asm/unistd_32.h’. Stop.
        make: *** [archheaders] Error 2
      - anil_pugalia November 6, 2014 At 3:10 PM
        
        Seems like the source tree doesn’t contain the correct headers &/or Makefile scripts. Try “sudo make prepare”
      - paras gupta November 6, 2014 At 5:44 PM
        
        actually i have a doubt
        i have 3 folders under /usr/src/
        1) linux-headers-3.13.0-24
        2) linux-headers-3.13.0-24-generic
        3) virtualbox-guest-4.3.10
        in which folder do i run the commands…1 or 2?
        
        BTW….i run ‘sudo make prepare’ in both of them
        output is—
        scripts/kconfig/conf –silentoldconfig Kconfig
        make[1]: *** No rule to make target `/usr/src/linux-headers-3.13.0-24-generic/arch/x86/syscalls/syscall_32.tbl’, needed by `arch/x86/syscalls/../include/generated/uapi/asm/unistd_32.h’. Stop.
        make: *** [archheaders] Error 2
      - anil_pugalia November 7, 2014 At 11:56 AM
        
        Difference between 1 & 2 may not be much except the extra version.
        
        Errors point to something missing in the folders – may be try building your driver without this *prepare commands.
      - paras gupta November 7, 2014 At 12:08 PM
        
        this command “make -C /usr/src/linux-headers-3.13.0-24-generic SUBDIRS=…modules”
        
        outputs—
        make: Entering directory `/usr/src/linux-headers-3.13.0-24-generic’
        
        /usr/src/linux-headers-3.13.0-24-generic/arch/x86/Makefile:113: CONFIG_X86_X32 enabled but no binutils support
        
        mkdir: cannot create directory ‘…modules’: Permission denied
        
        scripts/Makefile.build:44: /usr/src/linux-headers-3.13.0-24-generic/…modules/Makefile: No such file or directory
        
        make[1]: *** No rule to make target `/usr/src/linux-headers-3.13.0-24-generic/…modules/Makefile’. Stop.
        
        make: *** [_module_…modules] Error 2
        
        make: Leaving directory `/usr/src/linux-headers-3.13.0-24-generic’
      - anil_pugalia November 8, 2014 At 9:57 AM
        
        Why are you doing so? And what is this …modules?
      - paras gupta November 8, 2014 At 11:36 AM
        
        it’s a directory under /linux-3/13/0-24-generic/
        
        what should i do now to make the driver up and running?
      - anil_pugalia November 8, 2014 At 3:47 PM
        
        Yes, it is because of the version mismatch.
        
        Now, you may compile & install this new downloaded kernel and have your system boot with that. And then, you should be able to play around with your drivers.
suresh February 9, 2015 At 1:04 AM

what is the link for the next part of this ?

- anil_pugalia February 11, 2015 At 4:17 PM
  
  You may follow the series on my SysPlay’s blog, where the link’s to next articles are also provided towards the end of each article. The link to this first article on my blog is http://sysplay.in/blog/linux-device-drivers/2013/02/linux-device-drivers-for-your-girl-friend
  
Adam Wojnarski September 28, 2015 At 3:40 PM

I like to bash windows as the next guy BUT, M$ has been using hybrid kernels not needing restart for most drivers succesfully since NT4.0 (around 1996), 98 had a monolith kernel and needed restarts but XP(2001) used the hybrid approach and could load and unload drivers as well. Otherwise a very good post. Cheers

Aijaz March 31, 2018 At 11:26 AM

Hi Anil

Nice article series! Nevertheless, I have a doubt (don’t we all ;))

I’ve forgotten quite a few things and hence your posts are a wonderful revision. Now as far as I remember, one could not compile drivers without “linking against” a pre-compiled kernel since all those module related glue functions are defined there isn’t it? I was wondering why so many are asking about Linux Headers perhaps it is because by default only the headers are present (since we need those for applications) but then a more pertinent problem is of the version mismatch between the modules and the kernel.

Could you elaborate a bit more on that please? What that problem is and how do we typically resolve it?

- Aijaz March 31, 2018 At 11:29 AM
  
  Also more than just the module related glue functions, one typically uses a bunch of kernel functions and helpers for which we need to link against the kernel. So now what would happen if my ‘KERNEL_SRC’ would point to a version other than the running one? Will it still work in the sense will one be able to insert the module etc?
  
  - Anil Kumar Pugalia June 25, 2018 At 12:48 PM
    
    Now, kernel version match is mandatory.
    
Albin Paiyan August 1, 2018 At 5:25 PM

First thank you so much for this article, I am facing problem while running Make file, it’s through error as
Error: ubuntu@ubuntu:~/kernel$ sudo make
[sudo] password for ubuntu:
makefile:1: *** missing separator. Stop.
Am waiting for your reply

Anil Kumar Pugalia August 6, 2018 At 5:04 PM

Makefiles should compulsorily have tabs not spaces, so make sure that once you copy paste the Makefile, replace the bunch of spaces by a tab. Hope that helps.