RTM_BASE
#define RTM_NR_MSGTYPES (RTM_MAX + 1 - RTM_BASE)
#define RTM_FAM(cmd) (((cmd) - RTM_BASE) >> 2)
int msgindex = msgtype - RTM_BASE;
int type = cb->nlh->nlmsg_type - RTM_BASE;
type -= RTM_BASE;
if (type == RTM_GETLINK - RTM_BASE)
#define RTM_NR_MSGTYPES (RTM_MAX + 1 - RTM_BASE)
#define RTM_FAM(cmd) (((cmd) - RTM_BASE) >> 2)