Hi,

I am trying to learn Kernel Module Programming by referring

"The Linux Kernel Module Programming Guide" written by
Peter Jay Salzman and Ori Pomerantz downloaded from tldp.org

After some minor changes, the code gets compiled correctly, when I issue gcc -c firstmod.c.
I also see the oject file created named firstmod.o.

Problem is, whenever I try to insert the module by typing

insmod ./firstmod.o

I get an error stating that the module was not inserted because of some kernel compatibility issue.

I apologize for not providing the exact error message, but this is the gist of it.

Here is the code.

#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_ALERT */


int init_module(void)
{
printk("<1>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_ALERT Goodbye world 1.\n");
}


I am using Redhat 9.0

Please help me.


Regards,

Pritesh

Does it say that the module will taint the kernel, if so add a line MODULE_LICENSE("GPL");.

It is also possible that you have a kernel with versioning support compiled in. This appends a string to the end of each function name you register formed by encoding the parameters, return type, etc. This allows a module compiled for an older kernel to be loaded provided the functions used haven't changed their interface. To support versioning you have to #include <linux/modversions.h> (you may have to do something else too, I can't remember at the moment).

P.S. The KERN_ALERT should come outside the quotation marks.

Hi NHS,

Thank you for the reply.

However, if KERN_ALERT is put outside the quote, I get errors stating that it does not recongnize KERN_ALERT, that its an undeclared variable.
Regards,
Pritesh

I think you #include <linux/printk.h> to get KERN_ALERT.You could also try #include <linux/error.h>. If both fail then look in /usr/src/linux/include/linux/*.h for a likely looking file.

I think the commands

cd /usr/src/linux/include
for file in *.h; do grep '#define KERN_ALERT' $file >/dev/null 2>&1 && echo $file;done

should output each file which defines KERN_ALERT.

Back on a linux box, I've looked at some of my code and realised that your code was missing the lines
#define __KERNEL__
#define MODULE
before any of the #include lines. The __KERNEL__ symbol enables a lot of code that isn't used by user-space code but is by kernel code (eg. KERN_ALERT) and MODULE just includes the module specific code. This should sort your problem.