Accessing ifunit/ifaddr_byindex

[Brooks Davis]

On Thu, Mar 17, 2005 at 02:15:31PM +0100, Patrik Arlos wrote:
> Hi,
> 
> I'm writing a small program that tries to read out some parameters from a
> ifnet structure. The code used ifunit() to obtain the ifnet structure for
> the interface in question and later on it used ifaddr_byindex. The code
> compiles nicely, but fails miserably to link, with undefined references to
> the two mentioned functions. I've googled quite a lot (but obviously at the
> wrong places), but can't find what library to include.  I've included the
> code below, the compile command used is the following; 'gcc -o ifList.bsd
> -lpcap ifList.c'. The system is a FreeBSD-5.3-Release (?). 
> 
> If there are any other ways of finding the hw address and MTU for an
> Interface please let me know.

ifunit() and ifaddr_byindex() are both kernel functions and may not
be used in userland.  In fact, no program should access struct ifnet
directly from userland (though a few badly behaved ones do).  To get the
MTU, check the code if ifconfig that does it.  It's not all that hard,
though ifconfig obfuscates the process a fair bit.

-- Brooks

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