'flushing' printk to klogd

'flushing' printk to klogd

[Amir Hermelin]

Hi,
Is there any way to make sure klogd flushes printk output to
/var/log/messages before the circular buffer wraps?  I intend to use this
only during the development phase, but I find that during 'activity storms'
where lots of printk's are involved I lose some of the output.

Thanks,
Amir.

Re: 'flushing' printk to klogd

[Eugene Teo]

You can configure your syslog to output the messages to
a dedicated file. Also, you can increase the length
of your buffer:

352  #define LOG_BUF_LEN    (131072)
353  #elif defined(CONFIG_SMP)
354  #define LOG_BUF_LEN    (32768)
355 +#elif defined(CONFIG_VMSTAT_PFAULTS)
356 +#define LOG_BUF_LEN (1048576)
357  #else  
358  #define LOG_BUF_LEN    (16384) /* This must be a power of two */
359  #endif

Note that even if you flush printk output before the circular
buffer wraps, you will still likely to lose some output since
it doesn't take care of multiple writes at the same time.

Eugene

<quote sender="Amir Hermelin">
> Hi,
> Is there any way to make sure klogd flushes printk output to
> /var/log/messages before the circular buffer wraps?  I intend to use this
> only during the development phase, but I find that during 'activity storms'
> where lots of printk's are involved I lose some of the output.
> 
> Thanks,
> Amir.
> 
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

RE: 'flushing' printk to klogd

[Amir Hermelin]

Thanks Eugene

I've already changed the buf len (in my development version).  However, what
I really need is a way to flush the buffer before going into either heavy
log sections or, more importantly, fragile code sections.  So, if I'm in a
procedure that is safe to sleep, I can do the following:

int proc_ok_to_sleep()
{
	printk("these are the args we got" ....);
	flush_printk_to_syslog();
	/* Here starts the critical section, possibly will cause kernel
panic */
	....
}

Does a function such as the flush_printk_to_syslog() exists?

Thanks,
Amir.

-----Original Message-----
From: Eugene Teo [mailto:eugene.teo@eugeneteo.net] 
Sent: Sunday, November 09, 2003 6:10 PM
To: Amir Hermelin
Cc: linux-kernel@vger.kernel.org
Subject: Re: 'flushing' printk to klogd


You can configure your syslog to output the messages to
a dedicated file. Also, you can increase the length
of your buffer:

352  #define LOG_BUF_LEN    (131072)
353  #elif defined(CONFIG_SMP)
354  #define LOG_BUF_LEN    (32768)
355 +#elif defined(CONFIG_VMSTAT_PFAULTS)
356 +#define LOG_BUF_LEN (1048576)
357  #else  
358  #define LOG_BUF_LEN    (16384) /* This must be a power of two */
359  #endif

Note that even if you flush printk output before the circular buffer wraps,
you will still likely to lose some output since it doesn't take care of
multiple writes at the same time.

Eugene

<quote sender="Amir Hermelin">
> Hi,
> Is there any way to make sure klogd flushes printk output to 
> /var/log/messages before the circular buffer wraps?  I intend to use 
> this only during the development phase, but I find that during 
> 'activity storms' where lots of printk's are involved I lose some of 
> the output.
> 
> Thanks,
> Amir.
> 
> 
> -
> To unsubscribe from this list: send the line "unsubscribe 
> linux-kernel" in the body of a message to majordomo@vger.kernel.org 
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Re: 'flushing' printk to klogd

[Eugene Teo]

Hi Amir,

No, I don't think flush_printk_to_syslog exists but relevant
code in do_syslog can form our flush_printk_to_syslog().

In do_syslog, we can find the code to read the ring buffer:

232         while (!error && (log_start != log_end) && i < len) {
233             c = LOG_BUF(log_start);
234             log_start++;
235             spin_unlock_irq(&logbuf_lock);
236             error = __put_user(c,buf);
237             buf++;
238             i++;
239             spin_lock_irq(&logbuf_lock);
240         }

One way we can do is to add case 10 to do_syslog's switch, so that
we can call do_syslog(10, buf, count) when we want to flush the
printk to a log. 

We have to find a way to perform what is required in case 3, and in
our case, after we read the messages from the ring buffer, we want to 
flush it, so we do a logged_chars = 0; in the end.

But take note that __put_user() could sleep. Our messages could be
overwritten by other printks. 

If you are free, can you code it, and mail me the patch? I would have
coded it if not for my exams. Thanks.

Eugene

<quote sender="Amir Hermelin">
> Thanks Eugene
> 
> I've already changed the buf len (in my development version).  However, what
> I really need is a way to flush the buffer before going into either heavy
> log sections or, more importantly, fragile code sections.  So, if I'm in a
> procedure that is safe to sleep, I can do the following:
> 
> int proc_ok_to_sleep()
> {
> 	printk("these are the args we got" ....);
> 	flush_printk_to_syslog();
> 	/* Here starts the critical section, possibly will cause kernel
> panic */
> 	....
> }
> 
> Does a function such as the flush_printk_to_syslog() exists?
> 
> Thanks,
> Amir.
> 
> -----Original Message-----
> From: Eugene Teo [mailto:eugene.teo@eugeneteo.net] 
> Sent: Sunday, November 09, 2003 6:10 PM
> To: Amir Hermelin
> Cc: linux-kernel@vger.kernel.org
> Subject: Re: 'flushing' printk to klogd
> 
> 
> You can configure your syslog to output the messages to
> a dedicated file. Also, you can increase the length
> of your buffer:
> 
> 352  #define LOG_BUF_LEN    (131072)
> 353  #elif defined(CONFIG_SMP)
> 354  #define LOG_BUF_LEN    (32768)
> 355 +#elif defined(CONFIG_VMSTAT_PFAULTS)
> 356 +#define LOG_BUF_LEN (1048576)
> 357  #else  
> 358  #define LOG_BUF_LEN    (16384) /* This must be a power of two */
> 359  #endif
> 
> Note that even if you flush printk output before the circular buffer wraps,
> you will still likely to lose some output since it doesn't take care of
> multiple writes at the same time.
> 
> Eugene
> 
> <quote sender="Amir Hermelin">
> > Hi,
> > Is there any way to make sure klogd flushes printk output to 
> > /var/log/messages before the circular buffer wraps?  I intend to use 
> > this only during the development phase, but I find that during 
> > 'activity storms' where lots of printk's are involved I lose some of 
> > the output.
> > 
> > Thanks,
> > Amir.
> > 
> > 
> > -
> > To unsubscribe from this list: send the line "unsubscribe 
> > linux-kernel" in the body of a message to majordomo@vger.kernel.org 
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> 
> 
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

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