Changing MAX_PLUGINOUTPUT_LENGTH in include/objects.h

[Amri Karim]

Hi,

When changing the value of MAX_PLUGINOUTPUT_LENGTH in include/objects.h,
the pre flight check prints out a warning message about the
size of the service_message struct being longer than the
POSIX-guaranteed
atomic write size. This is the actual code in base/config.c:

/*****************************************/
/* check sanity of service message size...   */
/*****************************************/
if(sizeof(service_message)>512){
	snprintf(temp_buffer,sizeof(temp_buffer),
      "Warning: Size of service_message struct (%d bytes) is >
POSIX-guaranteed atomic write size (512 bytes).  Service checks results
may get lost or mangled!",sizeof(service_message));
		temp_buffer[sizeof(temp_buffer)-1]='\x0';
		write_to_logs_and_console(temp_buffer,
            NSLOG_VERIFICATION_WARNING,TRUE);
		warnings++;
	        }

There has been some discussion about changing 
MAX_PLUGINOUTPUT_LENGTH on this list bofore, I think. 
I found these two links to be interesting:

https://sourceforge.net/mailarchive/message.php?msg_id=6783947
http://article.gmane.org/gmane.network.nagios.user/6486/match=ipc+size

They suggest that this value is related to the 
BUF_SIZE setting of the OS.

If MAX_PLUGINOUTPUT_LENGTH has been bumped by 1000 bytes on a
custom install, I am wondering if this warning message can be 
ignored on a modern Linux system - from looking at 
include/linux/limits.h on a kernel tree and 
/usr/include/linux/limits.h, it appears that Linux uses a 
BUF_SIZE of 4096, well past the POSIX requirement of 512
bytes..

Can I just change base/config.c to reflect this before
compiling Nagios ? In other words, change the 512 on this line:

  if(sizeof(service_message)>512){

Additionally, is it safe to increase this value to, say,
10000 or so bytes ? Or is that an absolute no-go under
any circumstances.

Thanks in advance,
Karim


-------------------------------------------------------
This SF.Net email is sponsored by: Oracle 10g
Get certified on the hottest thing ever to hit the market... Oracle 10g. 
Take an Oracle 10g class now, and we'll give you the exam FREE.
http://ads.osdn.com/?ad_id149&alloc_id66&op=click