Re: ETHERMTU

[Guy Harris <guy () alum mit edu>]

On Sep 5, 2007, at 2:17 PM, Saikiran Madugula wrote:

> Yes, I get warning when gencode.c gets compiled with the custom  
> package.
> (ofcourse standalone libpcap compiles fine).
>
> gcc -O2 -I.  -I<path to custom package's include files> - 
> DHAVE_CONFIG_H  -D_U_="__attribute__((unused))" -D<XXX_ONLY> -fPIC - 
> DPIC -c ./gencode.c
> ./gencode.c:87:1: warning: "ETHERMTU" redefined
> In file included from /usr/include/netinet/if_ether.h:61,
>                 from /usr/include/netinet/ether.h:26,
> 		 from /pathtocustompackage/customheader.h                 		  
> from ./pcap-int.h:55,
>                 from ./gencode.c:65:

OK, so you have a *modified* version of gencode.c; this problem  
doesn't show up with *standard* libpcap.

> My apologies for loose terminology. I understand it is impossible to  
> predict what symbols might prop up. But to my surprise something  
> like ETHERMTU has been defined in that way and *I wish to only know  
> the reason behind this*

The reason behind this is that it's a perfectly reasonable name for  
the MTU of an Ethernet, that MTU being 1500 bytes (1500 bytes of  
Ethernet payload, after the 14-byte Ethernet header).

> If a package supports a OS such as Linux, is it not clean way of  
> being cautious of symbols that OS uses ?

No, there is no clean way to be cautious of symbols the OS uses,  
except not to use any symbols at all, which is a bit impractical.
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