Linux内核中的__KERNEL__是什么? [英] what is __KERNEL__ used for in linux kernel?

问题描述

谁可以解释以下代码的含义?

who can explain what does the following code means?

如果未定义__KERNEL__，请定义以下宏. 何时何地定义__KERNEL__?

if __KERNEL__ is not defined, define following macros. when and where define __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__ */

推荐答案

编译内核时，在命令行上定义了__KERNEL__.

When you compile your kernel, __KERNEL__ is defined on the command line.

用户空间程序需要访问内核头，但是内核头中的某些信息仅适用于内核.在#ifdef __KERNEL__/#endif块中包装一些语句可确保用户空间程序看不到这些语句.

User-space programs need access to the kernel headers, but some of the info in kernel headers is intended only for the kernel. Wrapping some statements in an #ifdef __KERNEL__/#endif block ensures that user-space programs don't see those statements.

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