About multi-line printk and the need (not) to repeat loglevel markers [Was: Re: [PATCH] ARM: mx3/pcm037: properly allocate memory for mx3-camera]

[Linus Torvalds]

10/11/23 Uwe Kleine-König <u.kleine-koenig at pengutronix.de>:
>
> BTW, I just noticed that Linus wrote:
>
>        Additionally, if no newline existed, one is added (unless the
>        log-level is the explicit KERN_CONT marker, to explicitly show
>        that it's a continuation of a previous line).
>
> This seems to be unimplemented, otherwise the output of
>
>        printk(KERN_ERR "foo bar baz ");
>        printk("buz\n" KERN_WARNING "fiz\n");
>
> should be
>
>        "foo bar baz \n" at error level
>        "buz\n<4>fiz\n" at default level

No. The KERN_WARNING in the middle of a string is always totally
bogus. There is no "should be". It's just wrong.

The "\n" is added automatically iff there is a log-level marker at the
beginning of the string (with LOG_CONT being the exception). So

   printk("foo bar baz ");
   printk(KERN_WARNING "fiz\n");

should output two lines ("foo bar baz" with the default loglevel, and
"fiz" with KERN_WARNING). Even though there is no explicit "\n" there
for the first one.

But KERN_XYZ anywhere but in the beginning of the string do not
matter. Adding newlines changes none of that. It doesn't make the
marker beginning of the string, it just makes it beginning of the
line.

   Linus