[Nagiosplug-devel] system specific defines ... Was: check_dhcp - a possible addition

[Andreas Ericsson]

Stanley Hopcroft wrote:
> Dear Folks,
> 
> As pointed out by Mr Ericsson, check_dhcp will not build properly 
> without preprocessor symbols being defined (__bsd__ etc).
> 
> I thought this was necessary to select _completely_ different code to 
> get the MAC address of the interface from the system (eg BSD use raw 
> sockets, solaris and hpux use DLPI [and prob AIX ...], Linux uses a 
> Linux specific ioctl()).
> 
> Continuing down this path requires that configure.in and config.h.in be 
> patched to set these symbols depending on the value of 'host'.
> 
> While tbis is feasable, doing so is seems anti-autoconf and 
> anachronistic (although this is the way that fping seems to operate) - 
> it looks bad and probably is too.
> 
> What is a better way ?
> 

Make sure in the necessary plugins that they are being compiled with 
GCC. The default compile mode for gcc is -std=gnu89 (meaning c89 with 
GNU extensions) for versions until the c99 support started emerging (not 
sure where that was), and -std=gnu99 (meaning c99 with GNU extensions). 
GNU extensions means that most BSD features (all networking ones, some 
stringhandling ones) are available as well as the "pure" gnu extensions 
(such as asprintf(), which is being heavily used throughout all C plugins).

The code to accomplish the above is done as such;
#ifdef __GCC__
<code>
#else
int
main(void)
{
	puts("This plugin requires GNU extensions, and can't be properly 
compiled without GCC\n");
	return 0;
}
#endif

main must be present (unless this is done from autoconf, which would be 
neater) or there will be lots of errors during make. It could probably 
be put in utils.c or somewhere else which all plugins use, but only 
compiled #if !defined(__GCC__).

> Chuck the system specific stuff and let the user define the broadcast 
> interface _and_ the MAC address (simply set the hardware address in the 
> DISCOVER packet and let the server respond with an OFFER to the real 
> MAC) ?
> 

Broadcast interface should be enough, although it couldn't hurt with MAC 
address as well. I'll have a look at how the ISC client does it, as it 
ports nicely to virtually every unix available.

> Chuck the C version and build a Perl one (based on Net::DHCP or friends) 
> ?
> 

suid perl is not a very good idea, and I strongly disagree with having 
to install additional perl modules (yes, I know it's simple enough using 
the automated CPAN stuff).

> Leave the C version Linux specific (and prob put it back in  contrib/) 
> and or build a Perl one ?
> 

Nah. Make sure it's compiled by GCC and write in the suggested changes. 
It shouldn't be terribly complicated.

-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Lead Developer