about printk and console_loglevel

about printk and console_loglevel

[Siddu]

Hi all,
Hi all,

I am little stuck understanding this piece of code below and the way its
been working

Question: since KERN_INFO = 6 # which is msg_log_level
and as per code
*msg_log_level < console_loglevel*

 this line of printk is not supposed to show up in the dmesg log ? but it is
showing up . Why

cat /proc/sys/kernel/printk
4    4   1   7

console_loglevel = 4

printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus());


static void _call_console_drivers(unsigned start,
       unsigned end, int msg_log_level)
{
 if ((*msg_log_level < console_loglevel* || ignore_loglevel) &&
     console_drivers && start != end) {
   if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
     /* wrapped write */
     __call_console_drivers(start & LOG_BUF_MASK,
           log_buf_len);
     __call_console_drivers(0, end & LOG_BUF_MASK);
   } else {
     __call_console_drivers(start, end);
   }
 }
}

Thanks for any inputs !
-- 
Regards,
~Sid~
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about printk and console_loglevel

[Михаил Кринкин]

I think, that console and dmesg are not the same. console_loglevel mean
sumething like text terminal. parport and so on, but dmesg is independent
from this log level. You can write simple module like this:

#include <linux/module.h>
#include <linux/kernel.h>

int init_module(void) {
        printk(KERN_EMERG "EMERG: Hello World.\n"); printk(KERN_ALERT
"ALERT: Hello World.\n"); printk(KERN_CRIT "CRIT: Hello World.\n");
printk(KERN_WARNING "WARNING: Hello World.\n"); printk(KERN_NOTICE "NOTICE:
Hello World.\n"); printk(KERN_INFO "INFO: Hello World.\n");
printk(KERN_DEBUG "DEBUG: Hello World.\n"); return 0;
}

void cleanup_module(void) {
        printk("Bye :)");
}

and you see, that dmesg print everything (but /var/log/messages contained
only WARNING, NOTICE and INFO levels messages, for console_loglevel = 3)

2011/3/5 Siddu <siddu.sjce@gmail.com>

> Hi all,
> Hi all,
>
> I am little stuck understanding this piece of code below and the way its
> been working
>
> Question: since KERN_INFO = 6 # which is msg_log_level
> and as per code
> *msg_log_level < console_loglevel*
>
>  this line of printk is not supposed to show up in the dmesg log ? but it
> is showing up . Why
>
> cat /proc/sys/kernel/printk
> 4    4   1   7
>
> console_loglevel = 4
>
> printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus());
>
>
> static void _call_console_drivers(unsigned start,
>        unsigned end, int msg_log_level)
> {
>  if ((*msg_log_level < console_loglevel* || ignore_loglevel) &&
>      console_drivers && start != end) {
>    if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
>      /* wrapped write */
>      __call_console_drivers(start & LOG_BUF_MASK,
>            log_buf_len);
>      __call_console_drivers(0, end & LOG_BUF_MASK);
>    } else {
>      __call_console_drivers(start, end);
>    }
>  }
> }
>
> Thanks for any inputs !
> --
> Regards,
> ~Sid~
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
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about printk and console_loglevel

[Andrzej Kardas]

On 05.03.2011 19:42, Siddu wrote:
> Hi all,
> Hi all,
>
> I am little stuck understanding this piece of code below and the way 
> its been working
>
> Question: since KERN_INFO = 6 # which is msg_log_level
> and as per code
> *msg_log_level < console_loglevel*
>
>  this line of printk is not supposed to show up in the dmesg log ? but 
> it is showing up . Why

console_loglevel concern messages that should display on the CONSOLE not 
"dmesg" and controls if message is enough important (read: have prioryty 
below *console_loglevel) *to display it on the console. You must know 
that, kernel logs its messages into buffer (into the RAM) which have 
constant size, when you type dmesg, you simply read messages from that 
buffer (ring-buffer), so that why you see your line in dmesg.

What is more, there is deamon called syslog (rsyslog) which reads this 
buffer periodically and saves messages in appropriate log file on the 
hard drive e.g. /var/log/kern.log or /var/log/messages etc. You can 
configure rsyslog as you wish, to log certain types messages into logfiles.


--
regards
Andrzej Kardas
http://www.linux.mynotes.pl
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about printk and console_loglevel

[Siddu]

Thank you ... I guess that answers :)

On Sun, Mar 6, 2011 at 3:52 AM, Andrzej Kardas <andrzej-kardas@o2.pl> wrote:

>
>
> On 05.03.2011 19:42, Siddu wrote:
>
> Hi all,
> Hi all,
>
>  I am little stuck understanding this piece of code below and the way its
> been working
>
> Question: since KERN_INFO = 6 # which is msg_log_level
> and as per code
> *msg_log_level < console_loglevel*
>
>   this line of printk is not supposed to show up in the dmesg log ? but it
> is showing up . Why
>
>
> console_loglevel concern messages that should display on the CONSOLE not
> "dmesg" and controls if message is enough important (read: have prioryty
> below *console_loglevel) *to display it on the console. You must know
> that, kernel logs its messages into buffer (into the RAM) which have
> constant size, when you type dmesg, you simply read messages from that
> buffer (ring-buffer), so that why you see your line in dmesg.
>
> What is more, there is deamon called syslog (rsyslog) which reads this
> buffer periodically and saves messages in appropriate log file on the hard
> drive e.g. /var/log/kern.log or /var/log/messages etc. You can configure
> rsyslog as you wish, to log certain types messages into logfiles.
>
>
> --
> regards
> Andrzej Kardas
> http://www.linux.mynotes.pl
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>


-- 
Regards,
~Sid~
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