Difference between printk and pr_info

Question

What's the exact difference between printk and pr_info functions ? And under what conditions, should I choose one over the another ?

All those are equivalent except debug one. – 0andriy Feb 15 '17 at 22:37 — 0andriy, Feb 15 '17 at 22:37

score 23 · Accepted Answer · edited Feb 15 '17 at 09:38

23

The kernel's printk.h has:

#define pr_info(fmt,arg...) \
    printk(KERN_INFO fmt,##arg)

Just like the name, pr_info is printk with the KERN_INFO priority.

edited Feb 15 '17 at 09:38

CL.

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answered Feb 15 '17 at 07:49

barcelona_delpy

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Actually `#define pr_info(fmt, ...) eprintf(0, verbose, pr_fmt(fmt), ##__VA_ARGS__)` – LPs Feb 15 '17 at 08:24
Exception is `pr_debug()` vs. `printk(KERN_DEBUG)` and all derivatives. – 0andriy Feb 15 '17 at 22:38

score 10 · Answer 2 · answered Mar 08 '18 at 04:29

When looking specifically at pr_info, the definition will in turn use printk(KERN_INFO ... (as mentioned in barcelona_delpy's answer); however, the answer's source snippet appears to exclude the format wrapper pr_fmt(fmt) (as mentioned by LPs comment).

The difference to why you may use pr_info over printk(KERN_INFO ... is the custom formatting you can set. If you wish to prefix your messages in your module with printk, a method is to explicitly add your prefix on each line:

printk(KERN_INFO "mymodule: hello there\n");
// outputs "mymodule: hello there"

or:

printk(KERN_INFO KBUILD_MODNAME " hello there\n");
// outputs "mymodule: hello there"

However, if you use pr_info (and other pr_* functions), you can re-define the format and simply use pr_info without additional work:

... (includes)
#ifdef pr_fmt
#undef pr_fmt
#endif
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

...
{
    ...
    pr_err("hello there\n");
    // outputs "mymodule: hello there" (assuming module is named 'mymodule')
    ...
}
...

Difference between printk and pr_info

2 Answers2