Programming :: Writing To Console From Kernel Module
Mar 2, 2011
I'm currently doing a tutorial for writing kernel modules. Right now I'm still at the very beginning, i.e. writing my helloworld stuff.
But what I like to do now is to write stuff onto the console, and I don't get it. According to my tutorials I can print stuff on the console using the printk()-function as long as the priority-level of the macro used in printk() is lower than the console_loglevel (how can I find that value out btw?).
But it doesn't work for me. Even if I use KERN_EMERG it still gets only logged, but not printed on the console and I thought KERN_EMERG get always printed...
Here's my code:
Code:
Code:
Everything works fine. But as soon as there are any blanks in mystring, e.g.
Code:
I always get
Code:
Why do I get this error and how can I insert string with blanks?
I am trying to learn how to write a kernel module. I am following the excellent guide from The Linux Documentation Project called The Linux Kernel Module Programming Guide v.2.6.4.
My machine is running Ubuntu Lucid Lynx (10.04)
Code:
I installed the corresponding linux headers and just to make sure I also installed the linux source and extracted it in /usr/src
I am trying to run the following trivial kernel module
i have written some really basic loadable kernel modules. There are a couple of concepts that i'll like to get cleared.
In a tutorial, the Makefile was given as follows- obj-m += try.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
I understand that -C option of 'make' changes the current directory to /lib/modules/$(shell uname -r)/build (which depends on my kernel).
Now, my question is why to change to that particular directory? Also M=$(PWD) will hold the dir where i have written the module. Why is it required? What does 'modules' at the end of that line indicate?
Q2> We need to include <linux/module.h> and <linux/kernel.h> in a module. If i am right, the module uses kernel headers for these definitions. But how does 'make' find these definitions.
Q3> We are planning to write a custom scheduler for linux kernel. cat /sys/block/sda/queue/scheduler gives us the currently loaded schedulers. How do we expose our scheduler to linux kernel so that we can use it by switching to it.
I'm trying to write a simple, console based application in linux, in c++. I know how to start in Eclipse and I have some experience in c++ from Windoze. I would like to ask, if there is some tutorial available on writing console apps. I mean, I know from using linux that there are two conventions on using parameters in command line (-v and --version for example).
do you have any code to flash led lights with paralel port (device driver programming)or any lecture about this subject .if there is a working code this would be better ofcourse.
I'm trying to build the kernel module for dvbhdhomerun. The problem is the linux kernel headers provided by Debian do not have the dvb header files. Trying to set up my own kernel source tree to use is not working out so well.
I'm following the instructions in the Debian section here: [URL] ....
My first try compiled, but the modules ender up under /lib/modules/3.2.51/extra instead of /lib/modules/3.2.0-4-amd64/extra. Why?
I tried to start over, but noticed this while running apt-get source linux-image-3.2.0-4-amd64:
Code: Select allReading package lists... Done Building dependency tree Reading state information... Done Picking 'linux' as source package instead of 'linux-image-3.2.0-4-amd64' NOTICE: 'linux' packaging is maintained in the 'Svn' version control system at: svn://svn.debian.org/svn/kernel/dists/trunk/linux/
[Code] ....
The failure to verify the signature has me concerned, but beyond that, what do I do about the different version number when compiling and installing the kernel modules?
I`m trying to compile sources of kernel module which has been written for kernel 2.6.9. There were many changes in kernel headers since then in current kernel sources. I`ve found that old /asm/system.h was moved under architecture dedicated directory /arch/*/include/asm/system.h. Anyway during sources compilation I`m having errors related to kernel sources. It looks like there is something wrong with this /asm/system.h
Code:
../asm/system.h: In function �__cmpxchg�: ../asm/system.h:248: error: expected string literal before �LOCK_PREFIX� ../asm/system.h:254: error: expected string literal before �LOCK_PREFIX�
I am looking for information to insert kernel module into kernel. I am not looking at dynamically insert of kernel module using insmod, modprobe etc. I am looking for statically insertion of kernel module procedure, such as what to change on makefile, what to change on menuconfig, what to change on .config file, etc.
There is a file called elevator.c. It is written as a module (i.e it has specific init and exit functions). However we are not able to see it in lsmod listing. We are working on a project where we need to modify this file. Compiling every time we change something will be time consuming. Is it possible to compile just this file and insert it as a normal module?
I have just started learning Device driver programming in Linux and am stuck in my first program. Its just to see init_module and cleanup_module calls to use printk and see results using dmesg. program is:
Code:
#define MODULE #include<linux/module.h> int init_module(void)
I'm trying to compile a Linux kernel module called hello-2.c using the command "make -C /lib/modules/$(uname -r)/build M=${PWD} modules" (without the quotes) (which I found online), and the following is the (seemingly successful) output.:
There is a module A which is compiled with the kernel. I wrote an external module B which exported a symbol using EXPORT_SYMBOL.The module A now needs to talk with that exported symbol (function call). For that i modified A so that it includes the function call from B. However i now get unidentified symbol errors during 'make' operation as symbols of B are not present during kernel compile and A now kind of depends on B.
One solution is that make B part of the kernel as well. However, it would mean that whenever now i try to compile a kernel with a different source, i have to modify the config files and everything to accommodate B.Hence i am seeking a solution which does not include modifying the kernel.
I'm trying to debug a module I programmed but I don't want to do it on the running host but against UML (don't want to reboot every 5 minutes).
The UML kernel I downloaded is 2.6.38.2. I have already downloaded the ubuntu kernel headers for this version (they belong to natty though I'm running maverick.... when I installed the .deb file with dpkg I had no problem at all).
Now I'd like to build said module against these headers. How can I do it?
How can we fire a shell command like ls,./a.out automatically in kernel space via a kernel module ? i.e. replacement of system() function of user space into kernel space.We need to develop a kernel module which can fire some shell command let say "firefox [url]" automatically to open google automatically from module.
I'm currently working with wireless network kernel module.
This device initialiy gets its IP address by using DHCP, but the problem is sometimes the new IP assigned for internal reason.
So what I want to do is assigning new(changed)IP address into exsiting interface, or occuring DHCP renew event to cause update IP from kernel level. This shold be done without user's intervention, so whenever the kernel module detects IP changed(via underlying wireless communication), it automatically correct update its IP address.
Q1) any functions or api to cause DHCP renew event from kernel level? Q2) or any functions or api to assign IP address to specific interface?
I want to be able to access my email account from the console. I'm reading all day about fetchmail, postfix, sendmail etc. but all the stuff I found is related to building whole mail system. All I want to do is to read my emails and write some. Which is the painless way to do this? I successfully configured Evolution for this purpose but I want to do that from the console.
This for Kernel 2.6.29.6. I'm trying to code a kernel module that displays process information.
how to count opened file descriptors per task. I have been able to write a module that lists all the current process names along with their pid number in /var/log/messages. Basically, I cycle through the ring of processes using the macro for_each_process(task) and printk the comm and pid of each task. I'm trying to see how many file descriptors each task has open. I've been reading up in books and all over the internet. At first I thought I needed to access max_fds under files_struct, but that just lists the maximum number of file descriptors that can be opened per task, which by default is set at 256. I then thought about counting the elements in the fd_array. But then I learned that every task's fd_array is initially set at 32. Now I know that I need to access open_fds of type fd_set * in files_struct. open_fds is a pointer to all the open file descriptors. The problem is that I don't know how to access a pointer of type fd_set.
Is there a good guide or book that really focuses on type fd_set and open_fds? Every book and resource I've read never really go into depth on this. relationship between files struct, open_fds, and the open file descriptors in task?
I need to install module u32 into the netfilter module for kernel 2.6.27.
I did not see the source code in the kernel version I have. where can I find the code for U32 module.
I have checked "netfilter.org" and looks like POM is discontinued. Is the u32 module committed to kernel version 2.6.27 or need to patch it. If yes, where can I find the patch?
I wrote a character device driver for an Embedded Linux build (Kernel Revision 2.6.17.1) running on ARM9. In the module's "read()" function, I'm returning the number of bytes that were copied into the user buffer. I saw some module code samples online and in most cases the "read()" function is returning the number of bytes read.The very strange behavior I saw in my case was, if I use a variable to return the value from the module's "read()" function, the user application reading from the module always saw "0".For instance:
I have a problem with my custom kernel when I want to create the Nvidia kernel module.After this finished I installed the image and headers and created the Nvidia kernel module. Everything worked fine.However, if I remove the linux-source from my home directory then I can't create the kernel module.Even though I have the headers for the kernel installed.
I'm running Virtualbox from the Sun website (need the USB support) and it breaks after each kernel update.The problem is that I installed a lot of Ubuntu systems for transitioning windows users with Windows in virtualbox to ease the migration but I have to rerun vboxdrv setup after each kernel patch.
I am interested in using fortran and an external library called matio used to save arrays to matlab .mat files. I have installed the matio and matio-dev packages from synaptics but i cannot compile a code receiving an error Code: christos@christos-laptop:~/Desktop$ gfortran -o test test.f90 -lmatio -lz test.f90:2.13: USE MATIO 1
Fatal Error: Can't open module file 'matio.mod' for reading at (1): No such file or directory How can i load a module in order to use it in fortran through the GCC compiler?
I am going to write a TCP server program using c. Can anyone give me some advices on whats and what not to do specially when using select?
There would be a lot of data to be transferred both on the server and back to the client. I already have a simple server here but the server uses a lot of resources. Maybe 3 to 4 connections and the server's load would rise to unacceptable levels.
Which do you think is better to use fork or select?
I want to write some PHP for a website that'll have the data that the script will generate written inside a table with thin black line around it, much like LQ itself. My problem is: how do I draw the box that the text will be inside of, since the amount of text will vary - if I have a GIF with a picture of a box, that'll be of a fixed length, and my script can then only generate that much text, for it to look nice. Or do I need to fiddle with the GD library to get done what I want?
