early_param和__setup宏

一.宏的定义

在/include/linux/Init.h中

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

 

#define early_param(str, fn)    \
__setup_param(str, fn, fn, 1)

两个宏都会调用__setup_param

跟踪进__setup_param宏的定义

#define __setup_param(str, unique_id, fn, early)            \
    static const char __setup_str_##unique_id[] __initconst \
        __aligned(1) = str;                 \
    static struct obs_kernel_param __setup_##unique_id      \
        __used __section(.init.setup)           \
        __attribute__((aligned((sizeof(long)))))        \
        = { __setup_str_##unique_id, fn, early }

 这个宏里面有个结构体obs_kernel_param

struct obs_kernel_param {
    const char *str;
    int (*setup_func)(char *);
    int early;
};

 

结合上面两个宏和一个结构体展开__setup

__setup(str, fn)宏定义了

一个static const char  __setup_str_fn[]变量=str

接着定义了

一个static struct obs_kernel_param __setup_fn结构体,并赋值(标记编译进.init.setup段)

{

    str;

    fn(char *); 

    0,或1

}

二.宏的作用

1.编译相关

在/include/asm-generic/Vmlinux.lds.h文件中定义了__setup_start.....__setup_end段

#define INIT_SETUP(initsetup_align)         \
        . = ALIGN(initsetup_align);     \
        VMLINUX_SYMBOL(__setup_start) = .;  \
        *(.init.setup)          \
        VMLINUX_SYMBOL(__setup_end) = .;

标记了.init.setup的函数会被编译进该段

2.内核启动的相关调用关系

在start_kernel中调用parse_early_param()

void __init parse_early_param(void)
{
    static __initdata int done = 0;
    static __initdata char tmp_cmdline[COMMAND_LINE_SIZE];
    if (done)
        return;
    strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE); //复制启动命令行数据
    parse_early_options(tmp_cmdline);   //调用parse_early_options函数
    done = 1;
}

parse_early_options函数

void __init parse_early_options(char *cmdline)
{
    parse_args("early options", cmdline, NULL, 0, do_early_param);
}

接着调用parse_args函数

int parse_args(const char *name,char *args,const struct kernel_param *params,unsigned num,int (*unknown)(char *param, char *val))
{
    char *param, *val;
    DEBUGP("Parsing ARGS: %s\n", args);

    args = skip_spaces(args);

    while (*args) { //遍历启动命令行
        int ret;
        int irq_was_disabled;

        args = next_arg(args, ?m, &val);    //获取下一个参数,填充param和val参数(例如:param--console;val--tty2,115200n8)
        irq_was_disabled = irqs_disabled();
        ret = parse_one(param, val, params, num, unknown);  //解析一个命令行参数
        if (irq_was_disabled && !irqs_disabled()) {
            printk(KERN_WARNING "parse_args(): option '%s' enabled ""irq's!\n", param);
        }
        switch (ret) {
        case -ENOENT:
            printk(KERN_ERR "%s: Unknown parameter `%s'\n",name, param);
            return ret;
        case -ENOSPC:
            printk(KERN_ERR "%s: `%s' too large for parameter `%s'\n",name, val ?: "", param);
            return ret;
        case 0:
            break;
        default:
            printk(KERN_ERR"%s: `%s' invalid for parameter `%s'\n",name, val ?: "", param);
            return ret;
        }
    }

    /* All parsed OK. */
    return 0;
}

命令行参数的解析parse_one

static int parse_one(char *param,char *val,const struct kernel_param *params,unsigned num_params,int (*handle_unknown)(char *param, char *val))
{
    unsigned int i;
    int err;

    /* Find parameter */
    for (i = 0; i < num_params; i++) {   //num_params=0
        if (parameq(param, params[i].name)) {
            if (!val && params[i].ops->set != param_set_bool)
                return -EINVAL;
            DEBUGP("They are equal!  Calling %p\n",params[i].ops->set);
            mutex_lock(?m_lock);
            err = params[i].ops->set(val, ?ms[i]);
            mutex_unlock(?m_lock);
            return err;
        }
    }

    if (handle_unknown) {   //若handle_unknown函数存在
        DEBUGP("Unknown argument: calling %p\n", handle_unknown);
        return handle_unknown(param, val);  //则调用handle_unknown函数,参数为param,val
    }

    DEBUGP("Unknown argument `%s'\n", param);
    return -ENOENT;
}

回溯回去handle_unknow函数就是do_early_param

static int __init do_early_param(char *param, char *val)
{
    const struct obs_kernel_param *p;

    for (p = __setup_start; p < __setup_end; p++) {
        if ((p->early && strcmp(param, p->str) == 0) || (strcmp(param, "console") == 0 && strcmp(p->str, "earlycon") == 0)) {
            if (p->setup_func(val) != 0)
                printk(KERN_WARNING"Malformed early option '%s'\n", param);
        }
    }
    /* We accept everything at this stage. */
    return 0;
}

do_early_param函数从__setup_start遍历到__setup_end段,

判断参数,进入if函数体里面

if (p->setup_func(val) != 0)这句调用了对应setup_func或early_param成员的函数,并将val作为其参数,val其实便是__setup(str, fn)或__early_param中的str

其实就是调用了fn(str)
这里的第一条if会刷选掉__setup定义的情况(除了console和earlycon参数的),因为__setup定义的obs_kernel_param结构体p->early=0

__setup定义的fn会在start_kernel->parse_args("Booting kernel", static_command_line, __start___param,__stop___param - __start___param,&unknown_bootoption);

unknown_bootoption->obsolete_checksetup函数给调用
看start_kernel中调用顺序

parse_early_param();
parse_args("Booting kernel", static_command_line, __start___param, __stop___param - __start___param,&unknown_bootoption);

可见先调用__early_param定义的解析参数函数及__setup定义的(console及earlycon)的参数解析函数

接着再调用__setup定义的其他解析参数函数