How to do it...

In the previous example, we saw that we can use the printk() function to generate kernel messages, but there are other functions that we can use in place of printk() in order to have more efficient messages and compact and readable code:

1. Use the following macros (as defined in the include/linux/printk.h file), which are listed in the following:

#define pr_emerg(fmt, ...) \
        printk(KERN_EMERG pr_fmt(fmt), ##__VA_ARGS__)
#define pr_alert(fmt, ...) \
        printk(KERN_ALERT pr_fmt(fmt), ##__VA_ARGS__)
#define pr_crit(fmt, ...) \
        printk(KERN_CRIT pr_fmt(fmt), ##__VA_ARGS__)
#define pr_err(fmt, ...) \
        printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__)
#define pr_warning(fmt, ...) \
        printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
#define pr_warn pr_warning
#define pr_notice(fmt, ...) \
        printk(KERN_NOTICE pr_fmt(fmt), ##__VA_ARGS__)
#define pr_info(fmt, ...) \
        printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)

1. Now, to generate a kernel message, we can do the following: looking at these definitions, we can rewrite our dummy_code_init() and dummy_code_exit() functions from the previous example into the dummy-code.c file, as follows:

static int __init dummy_code_init(void)
{
        pr_info("dummy-code loaded\n");
        return 0;
}

static void __exit dummy_code_exit(void)
{
        pr_info("dummy-code unloaded\n");
}