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SubjectRe: [PATCH 2/2] printk: Remember the message level for multi-line output
On Mon, Apr 14, 2008 at 10:03:51AM +0200, Ingo Molnar wrote:
>
> * Nick Andrew <nick@nick-andrew.net> wrote:
>
> > printk: Remember the message level for multi-line output
> >
> > printk(KERN_ALERT "Danger Will Robinson!\nAlien Approaching!\n");
> >
> > At present this will result in one message at ALERT level and one at
> > the current default message loglevel (e.g. WARNING). This is
> > non-intuitive.
> >
> > Modify vprintk() to remember the message loglevel each time it is
> > specified and use it for subsequent lines of output which do not
> > specify one, within the same call to printk.
>
> i've applied this too for testing.
>
> but multi-line strings are a bit unclean i think: each message line
> should have its separate printk.

You'd think. But there are a lot of calls to printk() with multi-line
format strings; developers clearly expect it to "just work" and
that a message level set at the start will be retained across lines.

> will your patch leave the behavior of multiple calls to printk alone?
> I.e. if i do:
>
> printk(KERN_ALERT "Danger Will Robinson!\n");
> printk("Alien Approaching!\n");
>
> then we'll still get a KERN_ALERT plus a default printk, right?

Yes, quite. The state of whether we're inside a line is retained
across calls to printk (from anywhere in the system) - this allows
code like this to usually do what you expect:

printk(KERN_ERR "Error:");
for (i = 0; i < 16; ++i) {
printk(" %02x", i);
}
printk("\n");

But in your example the first printk call contains a \n at the
end of the line and so upon entry to the second printk call
the function knows a new line is beginning.

The message level is a local variable. It's set to the default
at function entry, and is recalculated at the beginning of each
new line. It's changed only if a new line begins with a token.
So subsequent new lines which don't contain a token reuse the
previous value ... only within a single call to printk().

Nick.
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