The following minimal test program:
#include <net/if.h>
#include <linux/rtnetlink.h>
int main (int argc, char **argv) { return 0; }
compiled successfully in Ubuntu 10.10, but fails in the in-development Natty series (libc6-dev 2.12.1-0ubuntu8, linux-libc-dev 2.6.37-2.10) as follows:
$ gcc -Wall t.c -o t
In file included from /usr/include/linux/netdevice.h:28:0,
from /usr/include/linux/rtnetlink.h:9,
from t.c:2:
/usr/include/linux/if.h:135:8: error: redefinition of ‘struct ifmap’
/usr/include/net/if.h:112:8: note: originally defined here
/usr/include/linux/if.h:169:8: error: redefinition of ‘struct ifreq’
/usr/include/net/if.h:127:8: note: originally defined here
/usr/include/linux/if.h:218:8: error: redefinition of ‘struct ifconf’
/usr/include/net/if.h:177:8: note: originally defined here
So far, this problem has bitten busybox, wireless-tools, and NetworkManager.
This was triggered by a change in Linux 2.6.37-rc1 which added '#include <linux/netdevice.h>' to include/linux/rtnetlink.h, so I'm filing this bug on both libc and the kernel. It might be possible to work around this in the kernel in a way that's less intrusive to userspace applications, but really, I think the problem is that you can't include both <net/if.h> and <linux/if.h> (even transitively) at the same time. Until that's fixed, it's difficult to use the generic net headers together with Linux-specific features - note that there's no way to get at the functionality from <linux/rtnetlink.h> without including a <linux/*> header directly.
It's possible to work around this by shuffling includes to avoid using <net/if.h> and only use <linux/if.h> (you typically have to include <sys/socket.h> too), but it's messy and it would be better to steer in the direction of fewer <linux/*> inclusions in userspace applications, not more.
wpasupplicant is touched by this as well, both in its current version and the 0.7.3 packaging in Debian SVN.