Re: ETHERMTU

[Saikiran Madugula <hummerbliss () gmail com>]

Guy Harris wrote:
> Saikiran Madugula wrote:
> > I ran into this problem when I was trying to compile libpcap with a 
> > package which has support for a custom interface in Linux. I get a 
> > warning message about redefining ETHERMTU while compiling that package 
> > as the package uses net/ethernet.h.
>
> Do you get a warning message *when gencode.c is compiled*?

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:

the customheader includes net/ethernet.h. Which has ETHERMTU defined.

> If not, then there isn't a problem with gencode.c.
>
> > if gencode.c (or any other code) is indeed intended for use across 
> > several operating systems then it should be careful not pollute name 
> > space of the platforms it intends to be used on.
>
> gencode.c isn't polluting the name space.  Source files don't pollute 
> the name space - header files, such as ethernet.h, do.  It's impossible 
> to avoid using names that *might* be defined by *some* header file on a 
> system - even if you manage to avoid every name defined by the header 
> files in one release of a system, the next release might add a new symbol.
> -

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* and about the consequences.

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

Saikiran.


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