rk3188--2.linux-3.0.36中内核参数的读取与传递

一.内核参数的获取
1.1 kernel获取uboot传递的参数地址
a. 在arch/arm/kernel/head.S中,内核解压后就会跳到这个文件中
ldr r13, =__mmap_switched       @ address to jump to after
b. 在arch/arm/kernel/head-common.S中

__INIT
__mmap_switched:
    ....
    str    r9, [r4]            @ Save processor ID
    str    r1, [r5]            @ Save machine type
    str    r2, [r6]            @ Save atags pointer   //将参数地址保存在r6中
    bic    r4, r0, #CR_A       @ Clear 'A' bit
    stmia    r7, {r0, r4}      @ Save control register values
    b    start_kernel          //下一步进入c程序的start_kernel
ENDPROC(__mmap_switched)

    .align    2
    .type    __mmap_switched_data, %object
__mmap_switched_data:
    .long    __data_loc            @ r4
    .long    _sdata                @ r5
    .long    __bss_start           @ r6
    .long    _end                  @ r7
    .long    processor_id          @ r4
    .long    __machine_arch_type   @ r5
    .long    __atags_pointer       @ r6       //参数将会保存在__atags_pointer中
    .long    cr_alignment          @ r7
    .long    init_thread_union + THREAD_START_SP @ sp
    .size    __mmap_switched_data, . - __mmap_switched_data

1.2 将参数的读取到内核的过程
start_kernel
    --> setup_arch

void __init setup_arch(char **cmdline_p)
{
    struct machine_desc *mdesc;
    mdesc = setup_machine_fdt(__atags_pointer);  //这是个空函数,mdesc仍为NULL
    if (!mdesc)
        mdesc = setup_machine_tags(machine_arch_type);  //1.2.1
    machine_desc = mdesc;
    machine_name = mdesc->name;

    init_mm.start_code = (unsigned long) _text;
    init_mm.end_code = (unsigned long) _etext;
    init_mm.end_data = (unsigned long) _edata;
    init_mm.brk     = (unsigned long) _end;

    strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);
    *cmdline_p = cmd_line;    //将读取出来的参数赋给cmdline_p,一会就打印出来

    parse_early_param();     //这个函数在2.1分析-->内核参数的解析
}

1.2.1 查找machine_desc并取出参数
start_kernel
    --> setup_arch
        --> setup_machine_tags

static struct machine_desc * __init setup_machine_tags(unsigned int nr)
{
    struct tag *tags = (struct tag *)&init_tags;  //这个初始化实际上没有用
    struct machine_desc *mdesc = NULL, *p;
    char *from = default_command_line;
    init_tags.mem.start = PHYS_OFFSET;
    //查找当前的machine_desc结构体,即定义在board-rk3188-ds1006h.c中的
    //MACHINE_START(RK30, "RK30board")
    for_each_machine_desc(p)
        if (nr == p->nr) {
            printk("Machine: %s\n", p->name);
            mdesc = p;
            break;
        }
    //__atags_pointer=0x60000800
    if (__atags_pointer)
        tags = phys_to_virt(__atags_pointer);

    if (tags->hdr.tag == ATAG_CORE) {
        if (meminfo.nr_banks != 0)
            squash_mem_tags(tags);
        save_atags(tags);
        parse_tags(tags);       //1.2.1.1将参数复制到全局default_command_line中
    }
    //将uboot的参数复制到boot_command_line中
    strlcpy(boot_command_line, from, COMMAND_LINE_SIZE);

    return mdesc;
}

1.2.1.1  取参数到全局变量default_command_line
start_kernel
    --> setup_arch
        --> setup_machine_tags
        --> parse_tags
        --> parse_tag
            --> parse_tag_cmdline
在arch/arm/kernel/setup.c中

static void __init parse_tags(const struct tag *t)
{
    for (; t->hdr.size; t = tag_next(t))
        parse_tag(t);
}

继续调用

static int __init parse_tag(const struct tag *tag)
{
    extern struct tagtable __tagtable_begin, __tagtable_end;
    struct tagtable *t;

    for (t = &__tagtable_begin; t < &__tagtable_end; t++)
        if (tag->hdr.tag == t->tag) {
            t->parse(tag);
            break;
        }

    return t < &__tagtable_end;
}

继续调用

static int __init parse_tag_cmdline(const struct tag *tag)
{
    strlcpy(default_command_line, tag->u.cmdline.cmdline, COMMAND_LINE_SIZE);
}

---

二.内核参数的解析
2.1 整理一下流程
start_kernel
    --> setup_arch
    --> parse_early_param();
在init/main.c中

void __init parse_early_param(void)
{
    static __initdata int done = 0;
    static __initdata char tmp_cmdline[COMMAND_LINE_SIZE];

    strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
    parse_early_options(tmp_cmdline);
    done = 1;
}

2.2 将内核参数分解,并调用各个回调
start_kernel
    --> setup_arch
    --> parse_early_param();
        --> parse_early_options
在init/main.c中

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

这个函数有两个作用:
a是解析字符串
从uboot传入的字符串是：
Kernel command line: console=ttyFIQ0 androidboot.console=ttyFIQ0 init=/init initrd=0x62000000,0x00130000 mtdparts=rk29xxnand:0x00002000@0x00002000(misc),0x00004000@0x00004000(kernel),0x00008000@0x00008000(boot),0x00010000@0x00010000(recovery),0x00020000@0x00020000(backup),0x00040000@0x00040000(cache),0x00200000@0x00080000(userdata),0x00002000@0x00280000(kpanic),0x00100000@0x00282000(system),-@0x00382000(user) bootver=2013-06-20#1.24 firmware_ver=4.1.1
那么经过解析后的字符串是:
param=console, val=ttyFIQ0
param=androidboot.console, val=ttyFIQ0
param=init, val=/init
param=initrd, val=0x62000000,0x00130000
param=mtdparts, val=rk29xxnand:0x00002000@0x00002000(misc),0x00004000@0x00004000(kernel),0x00008000@0x00008000(boot),0x00010000@0x00010000(recovery),0x00020000@0x00020000(backup),0x00040000@0x00040000(cache),0x00200000@0x00080000(userdata),0x00002000@0x00280000(kpanic),0x00100000@0x00282000(system),-@0x00382000(user)
其中param与val都是两个char*,
b是对每一个param调用回调函数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++) {
        //p->early=1的,内核参数的名字与结构体名字相符合
        //这儿也解释了, 所有的内核代码里面都有early_initrd这个函数,
       // 却并不是每一个都会调用early_initrd,只有在内核参数中有initrd时才会调用
        if ((p->early && strcmp(param, p->str) == 0) ||
         (strcmp(param, "console") == 0 &&
             strcmp(p->str, "earlycon") == 0)
        )
       p->setup_func(val);     //对.init.setup段中符合条件的结构体,调用setup_func函数.
    return 0;
}

注1:     
    do_early_param只是对p->early=1的调用其setup_func   
    对p->early!=1的在函数obsolete_checksetup中执行
注2:early_initrd会不会每一个内核都执行?
      所有的内核代码里面都有这一句: early_param("initrd", early_initrd);为什么不是所有的内核都会执行early_intrd这个函数呢?
  [解释]:
      在do_early_param中,要想执行回调p->setup_func(这儿对应early_initrd),必须満足条件 strcmp(param, p->str) == 0.
      p->str是定义的结构体__setup_early_initrd的str="initrd"
      param是uboot传给kernel的参数中的参数,如果内核参数没有initrd,那么early_initrd就不会即行.    
      例如这个: root=/dev/mtdblock2 rootfstype=yaffs2 init=/linuxrc nconsole=tty1 console=ttySAC0,115200 就不会执行early_initrd     
注3: 这个p->setup_func这个指针是哪儿来的呢?
以early_param("initrd", early_initrd);为例说明一下:

其中early_param是定义在include/linux/init.h中
#define early_param(str, fn)                    \
    __setup_param(str, fn, fn, 1)

#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 }
展开后:
__setup_param("initrd", early_initrd, early_initrd, 1)
再展开:
static const char __setup_str_early_initrd[] __initconst __aligned(1) = "initrd";
static struct obs_kernel_param __setup_early_initrd    __used __section(.init.setup)
__attribute__((aligned((sizeof(long))))) = { __setup_str_early_initrd, early_initrd, early }
最终的展开形式:
static struct obs_kernel_param __setup_early_initrd    __used __section(.init.setup)
= { "initrd", early_initrd, 1 }
也就是定义了一个结构体:
struct obs_kernel_param {
    const char *str;
    int (*setup_func)(char *);
    int early;
};
其中section是定义在:arch/arm/kernel/vmlinux.lds中
. = ALIGN(16); __setup_start = .; *(.init.setup) __setup_end = .;
这样遍历段.init.setup就可以找到所有的结构体

start_kernel
    --> setup_arch
    --> parse_early_param();
        --> parse_early_options
            --> early_initrd
在arch/arm/mm/init.c中
param=initrd, val=0x62000000,0x00130000

static int __init early_initrd(char *p)  //只用了val,所以p=val
{
    unsigned long start, size;
    char *endp;
    start = memparse(p, &endp);
    if (*endp == ',') {
        size = memparse(endp + 1, NULL);

        phys_initrd_start = start;   //start=0x62000000
        phys_initrd_size = size;     //size=0x00130000
    }
    return 0;
}
early_param("initrd", early_initrd);