linux内核启动过程中__set_up的作用!

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__set_up是一个宏

#define __setup(str, fn)                    \
    __setup_param(str, fn, fn, 0)

#define __setup_param(str, unique_id, fn, early)                static char __setup_str_##unique_id[] __initdata = str;        static struct obs_kernel_param __setup_##unique_id            __attribute_used__                        __attribute__((__section__(".init.setup")))            __attribute__((aligned((sizeof(long)))))            = { __setup_str_##unique_id, fn, early }
struct obs_kernel_param {
    const char *str;
    int (*setup_func)(char *);
    int early;
};

#define __init        __attribute__ ((__section__ (".init.text")))
#define __initdata    __attribute__ ((__section__ (".init.data")))
#define __exitdata    __attribute__ ((__section__(".exit.data")))

举例:

static int __init init_setup(char *str)
{
    unsigned int i;

    execute_command = str;

    for (i = 1; i < MAX_INIT_ARGS; i++)
        argv_init[i] = NULL;
    return 1;
}
__setup("init=", init_setup);
//转换为
    static char __setup_str_init_setup[] __attribute__ ((__section__ (".init.data"))) ="init=";    
    static struct obs_kernel_param __setup_init_setup    
        __attribute_used__                
        __attribute__((__section__(".init.setup")))    
        __attribute__((aligned((sizeof(long)))))    
        = { __setup_str_init_setup, init_setup, 0 }
/*vmlinux.lds的.init段中
{
  ...
  __setup_start = .;
   *(.init.setup)
   __setup_end = .;
...
}*/
static
int __init obsolete_checksetup(char *line)/* Handle obsolete-style parameters */ { struct obs_kernel_param *p; int had_early_param = 0; p = __setup_start; /*从.init.setup段的开始分析*/ do { int n = strlen(p->str); /*计算出.init.setup中字符串的长度*/ if (!strncmp(line, p->str, n)) { if (p->early) { /*这里的都是early属性为0的*/ /* Already done in parse_early_param? * (Needs exact match on param part). * Keep iterating, as we can have early * params and __setups of same names 8( */ if (line[n] == \0 || line[n] == =) had_early_param = 1; } else if (!p->setup_func) { printk(KERN_WARNING "Parameter %s is obsolete," " ignored\n", p->str); return 1; } else if (p->setup_func(line + n))/*调用参数中对应函数,参数为偏移n个(初始化是参数长度)后的字符串*/ return 1; } p++; /*继续处理,直到结束*/ } while (p < __setup_end); return had_early_param; }
static int __init init_setup(char *str)
{
    unsigned int i;

    execute_command = str;
    /*
     * In case LILO is going to boot us with default command line,
     * it prepends "auto" before the whole cmdline which makes
     * the shell think it should execute a script with such name.
     * So we ignore all arguments entered _before_ init=... [MJ]
     */
    for (i = 1; i < MAX_INIT_ARGS; i++)
        argv_init[i] = NULL;
    return 1;
}
//作用就是把“=”后边的传给execute_command。
//比如设置了init=/linuxrc   则execute_command=&“/linuxrc” 表示不正确 就是那个结构体的str参数偏移n个的地址
static int noinline init_post(void)
{
        ...
    if (ramdisk_execute_command) {
        run_init_process(ramdisk_execute_command);
        printk(KERN_WARNING "Failed to execute %s\n",
                ramdisk_execute_command);
    }
        ...
    if (execute_command) {
        run_init_process(execute_command);
        printk(KERN_WARNING "Failed to execute %s.  Attempting "
                    "defaults...\n", execute_command);
    }
    run_init_process("/sbin/init");
    run_init_process("/etc/init");
    run_init_process("/bin/init");
    run_init_process("/bin/sh");

    panic("No init found.  Try passing init= option to kernel.");
}        

 









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