Nagios 2.0 - x86_64 - POSIX-guaranteed warning

[Eli Stair]

I've attached an email I saved a while back in relation to this.  I see 
the same issue when compiling 64-bit on any x86* platform & distro. 
Haven't had a chance to patch and test (or even read it...) this yet, 
let us know if it resolves the issue.

/eli

Tom Brown wrote:
> Hi
> 
> Just installed and run up my first 2.0 installation and this was 
> compiled and run on a x86_64 box running CentOS 4.2 - things seem to be 
> OK but running the pre-flight check i get this
> 
> Size of service_message struct (528 bytes) is > POSIX-guaranteed atomic 
> write size (512 bytes). Service checks results may get lost or mangled!
> 
> Is this something to be worried about??
> 
> thanks
> 
> 
> 
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It turns out that struct timeval is different 8-bytes verses 16-bytes. 
What if the value of MAX_PLUGINOUTPUT_LENGTH was calculated at compile 
time, based on the overall size of the service_message structure?  Of 
course, I think this would mean that all of your Nagios machines have to 
be of the same architecture?

I've recompiled with the two changes shown below... So far so good.



*** objects.h.orig      2006-01-19 15:46:13.000000000 -0500
--- objects.h   2006-01-19 15:46:25.000000000 -0500
***************
*** 45,51 ****

   #define MAX_HOSTNAME_LENGTH                           64      /* max. 
host name length */
   #define MAX_SERVICEDESC_LENGTH                        64      /* max. 
service description length */
- #define MAX_PLUGINOUTPUT_LENGTH                       348     /* max. 
length of plugin output */

   #define MAX_STATE_HISTORY_ENTRIES             21      /* max number 
of old states to keep track of for flap detection */

--- 45,50 ----




*** nagios.h.orig       2006-01-19 15:47:50.000000000 -0500
--- nagios.h    2006-01-19 15:47:26.000000000 -0500
***************
*** 389,394 ****
--- 389,396 ----
           }notification;


+ #define MAX_PLUGINOUTPUT_LENGTH 
512-MAX_HOSTNAME_LENGTH-MAX_SERVICEDESC_LENGTH-5*sizeof(int)-2*sizeof(struct 
timeval) /* max. length of plugin output */
+
   /* SERVICE_MESSAGE structure */
   typedef struct service_message_struct{
         char host_name[MAX_HOSTNAME_LENGTH];            /* host name */


-----Original Message-----
From:	nagios-users-admin at lists.sourceforge.net on behalf of Chris Waters
Sent:	Thu 01/19/2006 03:19 PM
To:	nagios-users at lists.sourceforge.net
Cc:	
Subject:	RE: [Nagios-users] Nagios 2.0rc2 on FC4 x86_64
I have the same issue on Nagios 2.06b FC4 x86_64 although I have not
seen an actualy problem arise from the warning yet that I can tell.


Chris Waters
WAN/LAN Technician
JELD-WEN, Inc.
Network Services Group
===================




-----Original Message-----
From: nagios-users-admin at lists.sourceforge.net
[mailto:nagios-users-admin at lists.sourceforge.net] On Behalf Of Miner,
Jonathan W (CSC) (US SSA)
Sent: Thursday, January 19, 2006 12:00 PM
To: nagios-users at lists.sourceforge.net
Subject: RE: [Nagios-users] Nagios 2.0rc2 on FC4 x86_64

I didn't modify "objects.h", so it must be the compiler padding things
differently for 64-bit.


-----Original Message-----
From:	nagios-users-admin at lists.sourceforge.net on behalf of Marc
Powell
Sent:	Thu 01/19/2006 02:32 PM
To:	nagios-users at lists.sourceforge.net
Cc:	
Subject:	RE: [Nagios-users] Nagios 2.0rc2 on FC4 x86_64



 >> -----Original Message-----
 >> From: nagios-users-admin at lists.sourceforge.net [mailto:nagios-users-
 >> admin at lists.sourceforge.net] On Behalf Of Miner, Jonathan W (CSC) (US

SSA)

 >> Sent: Thursday, January 19, 2006 11:29 AM
 >> To: nagios-users at lists.sourceforge.net
 >> Subject: [Nagios-users] Nagios 2.0rc2 on FC4 x86_64
 >>
 >> Hi -
 >>
 >> I've noticed an interesting warning when running Nagios on a 64-bit
 >> machine:
 >>
 >
 >>> > Warning: Size of service_message struct (528 bytes) is > POSIX-
 >
 >> guaranteed
 >
 >>> > atomic write size (512 bytes).  Service checks results may get lost

or

 >>> > mangled!
 >
 >>


The most probable reason for this is that you have modified the
MAX_HOSTNAME_LENGTH (64), MAX_SERVICEDESC_LENGTH (64) or
MAX_OLUGINOUTPUT_LENGTH (348) variables from their defaults in
include/objects.h. They are set so that the entire service_message
struct is < 512 bytes. If that's not the case then you may be seeing
compiler oddities that cause other structs or types (int, timeval) to be
larger than normal.


 >> How concerned should I be?  Should I be looking for a 32-bit machine

to

 >> host my production instance of Nagios?


While I can't tell you all the possible problems that might result, one
that I know is that if you are using passive checks, the results may get
lost or mangled because they're larger than what can usually be written
to a named pipe in one go. 32-bit vs 64-bit isn't a factor unless 64-bit
allows for larger pipes. The hostname length + service description
length + plugin output length would have to be > ~480 bytes to be
worrisome.

--
Marc


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