I played dumb and tried to see how far it could lead me along. Despite the mistakes, there is indeed an algorithm present for printing a message every 5 seconds. It’s like two separate module examples were concatenated together. It repeats module_init() and module_exit() twice. Anyway, at first glance you can tell this output has some issues. If you care, you can often get it to spit out the rest of the response if you ask it the right way. I’ve noticed that ChatGPT does that sometimes. TheĪt this point, I guess the response was too long so it got cut off. Then, run make to compile the kernel module. ![]() To use this Makefile, save the code above in a file named hello_world.c, and save the Makefile in the same directory. Make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean Make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules Here is a Makefile that can be used to compile the kernel module: Thread = kthread_run(thread_fn, NULL, "hello_world_thread") This function is called repeatedly by a kernel thread Sleep for 1 ms to avoid hogging the CPU Reset the jiffies counter so that we only print every 5 seconds If 5 seconds have passed, print "Hello world" Unsigned long time_since_load_sec = time_since_load / HZ Convert time in jiffies to time in seconds Unsigned long time_since_load = jiffies - jiffies_at_load Calculate the time that has passed since the module was loaded That file can be loaded into the kernel on the target system for testing.#include // Needed for all kernel modules The Linux build system should build the new kernel module and generate a ‘.ko’ file for it. To configure, run ‘make menuconfig’, find the new option and enable it (select ‘M’ to generate a kernel module). Once all of these changes are in place, the kernel can be configured and built with the new module. In these examples, ‘cmod’ is the folder containing the new module and CONFIG_MOD is an existing kernel option that the new custom module depends on. New lines must be added that refer to the new files, as in the following example: This is done by modifying the corresponding menu config file and make file in the parent folder. ![]() It contains one source file, ‘source_code.c’.Īfter the folder and files are in place, the Linux kernel needs a way to find them. The make file defines a kernel module called ‘custom-module.ko’. If it’s M it will be built as a kernel module. If it’s on, it will be built into the main kernel image. The menu config file defines a new menu option that can be set to either off, on or M. Obj- $(CONFIG_CUSTOM_MODULE) + = custom-module.o Tristate “Support for a Custom Linux Module” ![]() The new folder must contain a menu config file (Kconfig) and a make file (Makefile). The best parent folder depends on what the new modules does and what existing kernel features it builds on. Usually, the new module will have its own folder under an existing folder. Setting up Linux to build a new kernel module requires creating and modifying a few files in the kernel source code. Linux development using kernel modules can be more convenient than developing built-in code because the kernel modules are usually smaller than the entire kernel image, and they can usually be tested without re-booting the target system. A Linux kernel module contains code that can be added or removed from the kernel at runtime using command line utilities (insmod, rmmod).
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