有谁能解释一下以下代码的含义?
如果未定义__KERNEL__
,则定义以下宏。
何时和在哪里定义__KERNEL__
?
/* only for userspace compatibility */
#ifndef __KERNEL__
/* IP6 Hooks */
/* After promisc drops, checksum checks. */
#define NF_IP6_PRE_ROUTING 0
/* If the packet is destined for this box. */
#define NF_IP6_LOCAL_IN 1
/* If the packet is destined for another interface. */
#define NF_IP6_FORWARD 2
/* Packets coming from a local process. */
#define NF_IP6_LOCAL_OUT 3
/* Packets about to hit the wire. */
#define NF_IP6_POST_ROUTING 4
#define NF_IP6_NUMHOOKS 5
#endif /* ! __KERNEL__ */