内核模块编程中常用的宏的内核源码实现分析

/* Generic info of form tag = "info" */

#define MODULE_INFO(tag, info) __MODULE_INFO(tag, tag, info)

 

#define __MODULE_INFO(tag, name, info)                                           \

static const char __module_cat(name,__LINE__)[]                                      \

  __attribute__((__used__))                                                  \

  __attribute__((section(".modinfo"),unused)) = __stringify(tag) "=" info

 

#define ___module_cat(a,b) __mod_ ## a ## b

#define __module_cat(a,b) ___module_cat(a,b)

 

#define __stringify_1(x...)        #x

#define __stringify(x...)   __stringify_1(x)

 

MODULE_INFO(foo,bar) 则展开之后就是:

static const char __mod_foo##__LINE__[]  __attribute__((used))     \

__attribute__((section(“.modinfo”),unused)) = “foo=bar”

##__LINE__用MODULE_INFO这个语句在源文件中所在的行数替换。

 

 

#define MODULE_ALIAS(_alias) MODULE_INFO(alias, _alias)

举一反三… MODULE_INFO(“md-raid5”) 展开就是:

static const char __mod_alias##__LINE__[]  __attribute__((used)) \

         __attribute__((section(“.modinfo”),unused)) = “alias=md-raid5”

 

#define MODULE_LICENSE(_license) MODULE_INFO(license, _license)

举一反三…MODULE_LICENSE(“Dual BSD/GPL”)展开就是:

static const char __mod_license##__LINE__[]  __attribute__((used)) \

         __attribute__((section(“.modinfo”),unused)) = “license=Dual BSD/GPL”

 

#define MODULE_AUTHOR(_author) MODULE_INFO(author, _author)

MODULE_AUTHOR(“liangtao”)展开就是:

static const char __mod_author##__LINE__[]  __attribute__((used)) \

         __attribute__((section(“.modinfo”),unused)) = “author=liangtao”

 

#define MODULE_DESCRIPTION(_description) MODULE_INFO(description, _description)

MODULE_DESCRIPTION(“dummy”)展开就是:

static const char __mod_description##__LINE__[] __attribute__((used)) \

         __attribute__((section(“.modinfo”),unused)) = “description=dummy”

 

#define MODULE_VERSION(_version) MODULE_INFO(version, _version)

MODULE_VERSION(“0.0.1”)展开就是:

static const char __mod_version##__LINE__[]  __attribute__((used)) \

         __attribute__((section(“.modinfo”),unused)) = “version=0.0.1”

 

#define EXPORT_SYMBOL(sym)                                            \

         __EXPORT_SYMBOL(sym, "")

 

/* For every exported symbol, place a struct in the __ksymtab section */

#define __EXPORT_SYMBOL(sym, sec)                               \

         extern typeof(sym) sym;                                      \        首先声明sym是全局可用的

         __CRC_SYMBOL(sym, sec)                                           \        校验…version check

         static const char __kstrtab_##sym[]                         \

         __attribute__((section("__ksymtab_strings"), aligned(1))) \

         = MODULE_SYMBOL_PREFIX #sym;                            \

         static const struct kernel_symbol __ksymtab_##sym    \

         __used                                                             \

         __attribute__((section("__ksymtab" sec), unused))       \

         = { (unsigned long)&sym, __kstrtab_##sym }

 

例如:

EXPORT_SYMBOL(foo_var)展开为:
static const char __kstrtab_foo_var[] __attribute__((section(“__ksymtab_strings”).aligned(1))) \

         = “foo_var”;

static const struct kernel_symbol __ksymtab_foo_var __attribute__((used)) \

         __attribute__((section(“__ksymtab”),unused)) \

         = { (unsigned long)&foo_var, __kstrtab_foo_var }

 

extern struct module __this_module;

#define THIS_MODULE (&__this_module)