CODEWITHSUNDEEP
linux-kernelkernel-moduleprintk
Marco Montevechi Filho
Marco Montevechi Filho

Reputation: 193

Is printk() deprecated?

Asking this seems absurd to me but...

I'm reading Linux Device Drivers to learn how to create kernel modules. The book seems a bit old but I couldn't find a more recent version.

So I set up a Debian 12 virtual machine with VirtualBox, cloned the Linux kernel v6.4.3, recompiled and installed it.

Finally, in a different folder, I wrote the book's first simple "hello world" example which I show at the end of this question. It uses printk() to print a warning message in init and one in exit. Doing:

insmod hello.ko

Prints an empty line in my dmesg buffer, as shown in image below. Same for rmmod command. So I found this question and decided to change my

printk(KERNEL_WARNING, "Hello, World!\n")

to

pr_err("Hello, world!\n")

and now I have a decent line shown in dmesg. Am I doing something wrong? What is wrong with using printk()?

Code and image below:

#include <linux/init.h>
#include <linux/module.h>

MODULE_LICENSE("Duas BSD/GPL");

static int hello_init(void)
{
    // pr_err("Hello, world!\n"); // uncomment this line to get intended result
    printk(KERN_ERR, "Hello, world!\n");
    return 0;
}

static void hello_exit(void)
{
    printk(KERN_ERR, "Goodbye, world!\n");
}

module_init(hello_init);
module_exit(hello_exit);

dmesg result below. Blank spaces in dmesg result are generated by insmod hello.ko compiled with pr_err() line commented. "Hello world" line was generated by uncommenting pr_err() line.

Upvotes: 0

Views: 32

Answers (0)

Related Questions