On Sun, Dec 09, 2007 at 07:08:12PM +0530, Amogh Hooshdar wrote:
> I am a newbie in the world of Linux kernel. I have lots of questions
> and some may be really silly. So, I will be asking a lot of questions
> in the coming few months. I hope asking such questions is considered
> OK here. If not, please guide me. Here is the question I have now. I
> was playing with the printk() statements and how they work. I found a
> strange thing.
>
> printk(KERN_INFO "hello, world\n" KERN_INFO "hello, again\n");
>
> Initially, I was expecting it to print "hello world" in one line and
> "<6>hello, again" in the next line. But this is printing "hello,
> world" and "hello, again" in two different lines. So, is it that the
> printk() puts the whole message in some kernel buffer. and the kernel
> searches for PRIORITY-message-newline-PRIORITY-message-newline... and
> so on and prints into dmesg?
It's dmesg() (and klogd) that interpret the priority levels for you.
Here's a dmesg that dumps the raw kernel printk() buffer without any
interpretation:
#include <unistd.h>
#include <sys/syscall.h>
#include <errno.h>
#include <stdio.h>
static int my_syslog(int type, char *bufp, int len)
{
return syscall(__NR_syslog, type, bufp, len);
}
int main(void)
{
char buf[65536];
my_syslog(3, buf, 65535);
printf("buf: %s\n", buf);
return 0;
}
That should show you what's going on.
Erik
--
They're all fools. Don't worry. Darwin may be slow, but he'll
eventually get them. -- Matthew Lammers in alt.sysadmin.recovery
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