Several parameters that a driver needs to know can change from system to system. These can vary from the device number to use to numerous aspects of how the driver should operate.

This example shows how our kernel module get parameters from user at load time by insmod or modprobe.

To build this module, execute:

make KERNELDIR=/path/to/kernel/source/dir

If you have already set and exported KERNELDIR environment variable, simply execute make is enough.

If neither KERNELDIR environment variable nor KERNELDIR option of make are set, the current running kernel will be built against.

Copy hello_world.ko file to the target machine, then run:

insmod module_parameters.ko

Running dmesg | tail -10, you can find something like this:

[ 1141.505799] parameters test module is loaded
[ 1141.508953] #0 Hello, Mom

It is right that we defautly set to print hello, Mom only one time. Next we unload this module and pass parameters to it when loading.

# unload the module
rmmod module_parameters

# re-load the module and passing parameters to it
insmod module_parameters.ko whom=dady howmany=3

This time, the message is changed:

[ 1322.364784] parameters test module is loaded
[ 1322.366768] #0 Hello, dady
[ 1322.367999] #1 Hello, dady
[ 1322.369154] #2 Hello, dady