rk3188--4.android用initrd文件系统启动流程


在init/intramfs.c中

static
int __init populate_rootfs(void)

{

unpack_to_rootfs(__initramfs_start, __initramfs_size);
//1. initramfs的解压

if
(initrd_start) {

unpack_to_rootfs((char
*)initrd_start, initrd_end
- initrd_start);
//2.initrd的解压

free_initrd();

}

}

rootfs_initcall(populate_rootfs);
//这个相当于module_init在系统初始化时会调用

1. initramfs的解压

unpack_to_rootfs(__initramfs_start, __initramfs_size);

rootfs_initcall(populate_rootfs);

--> populate_rootfs

--> unpack_to_rootfs

在init/initramfs.c中

static char
* __init unpack_to_rootfs(char
*buf, unsigned
len)

{

int i;

int written, res;

decompress_fn decompress;

const char
*compress_name;

static __initdata char msg_buf[64];

header_buf
= kmalloc(110, GFP_KERNEL);

symlink_buf
= kmalloc(PATH_MAX
+ N_ALIGN(PATH_MAX)
+ 1, GFP_KERNEL);

name_buf = kmalloc(N_ALIGN(PATH_MAX),
GFP_KERNEL);

state = Start;

this_header
= 0;

message =
NULL;

while
(!message
&&
len)
{

loff_t saved_offset
= this_header;
//如果开头以字符'0'开始,说明这是cpio格式的ram disk,不用解压直接用复制

if
(*buf
==
'0'
&&
!(this_header
& 3))
{

state
= Start;

written
= write_buffer(buf,
len);

buf
+= written;

len
-= written;

continue;

}

}

dir_utime();

kfree(name_buf);

kfree(symlink_buf);

kfree(header_buf);

return message;

}

在initramfs.cpio中打包了3个文件(2个目录 1个字符设备文件):

/dev 目录

/dev/console 文件

/root 目录

dir
/dev 0755 0 0

nod /dev/console 0600 0 0 c 5 1

dir /root 0700 0 0

下面来看一下它们是如何依次解出来的:

buf=__initramfs_start, len=__initramfs_size

static
int __init write_buffer(char
*buf, unsigned
len)

{

count =
len;

victim = buf;

while
(!actions[state]())

;

return len
- count;

}

1.1 do_start

因为在initramfs.cpio的文件长度都为0,所以没有do_copy的过程

write_buffer

--> do_start

在init/initramfs.c中

static
int __init do_start(void)

{

//实际作用是将collect指针移动到打包的cpio每一个文件头处

read_into(header_buf, 110, GotHeader);

return 0;

}

注意:这个名虽然叫read_into而且第一个参数又是buf,但实际上这个buf没有起到任何作用

static void __init read_into(char
*buf, unsigned size, enum state
next)

{

if
(count >= size)
{

collected
= victim;

eat(size);

state =
next;
//下一步要执行do_header

}

}

1.2 do_header解析110字节的头

write_buffer

--> do_start

--> do_header

static
int __init do_header(void)

{

if
(memcmp(collected,
"070707", 6)==0)
{

error("incorrect cpio method used: use -H newc option");

return 1;

}

if
(memcmp(collected,
"070701", 6))
{

error("no cpio magic");

return 1;

}

parse_header(collected);
//从101个字节的头中解析出inod mode uid gid等

next_header
= this_header + N_ALIGN(name_len)
+ body_len;
//移到下一个文件的头处

next_header
= (next_header
+ 3)
& ~3; //cpio的头部都是4字节对齐的

state = SkipIt;

if
(name_len <= 0
|| name_len
> PATH_MAX)

return 0;

if
(S_ISLNK(mode))
{

if
(body_len
> PATH_MAX)

return 0;

collect
= collected = symlink_buf;

remains
= N_ALIGN(name_len)
+ body_len;

next_state
= GotSymlink;

state = Collect;

return 0;

}

//注意下面这个 !body_len,目录的body_len为0设备文件的body_len也为0

//所以这儿代表的是,所有非链接文件

if
(S_ISREG(mode)
||
!body_len)

read_into(name_buf, N_ALIGN(name_len),
GotName);
//这个实际的作用是,将指针移动到下一个文件的头处

return 0;
//并将状态改为GotName,即要调用do_name

}

1.3 do_name建立目录文件

write_buffer

--> do_start

--> do_header

--> do_name

进行到此处,系统中己存在/与/root两个目录(都是虚拟的),此时再把打包在cpio里面的文件解析到系统的相应位置上.

static
int __init do_name(void)

{

state = SkipIt;

next_state
= Reset;

if
(strcmp(collected,
"TRAILER!!!")
== 0)
{ //判断是不是结尾

free_hash();

return 0;

}

clean_path(collected, mode);
//把原先有的路径去掉, 相当于rmdir /dev 或 rm /dev/console

if
(S_ISREG(mode))
{

int ml
= maybe_link();

if
(ml >= 0)
{

int openflags
= O_WRONLY|O_CREAT;

if
(ml != 1)

openflags
|= O_TRUNC;

wfd
= sys_open(collected, openflags, mode);
//如果是普通文件打开sys_open

if
(wfd >= 0)
{

sys_fchown(wfd, uid, gid);
//设置权限等

sys_fchmod(wfd, mode);

if
(body_len)

sys_ftruncate(wfd, body_len);

vcollected
= kstrdup(collected, GFP_KERNEL);

state
= CopyFile; //最后调用do_copy将文件内容复制过来

}

}

}
else if
(S_ISDIR(mode))
{ // 以/dev为例


sys_mkdir(collected, mode);
// 创建 /dev目录

sys_chown(collected, uid, gid);
// 设置所有者

sys_chmod(collected, mode);
// 设置权限

dir_add(collected, mtime);
// 更改/dev目录的mtime

}
else if
(S_ISBLK(mode)
|| S_ISCHR(mode)
|| S_ISFIFO(mode)
|| S_ISSOCK(mode))
{

if
(maybe_link()
== 0)
{ // 以/dev/console为例

sys_mknod(collected, mode, rdev);
// 创建 /dev/console结点

sys_chown(collected, uid, gid);
//
[b]设置所有者[/b]

sys_chmod(collected, mode);
//
[b]设置权限[/b]

do_utime(collected, mtime); //
更改时间戳

}

}

return 0;

}

1.3 do_skip

write_buffer

--> do_start

--> do_header

--> do_name

--> do_skip

static
int __init do_skip(void)

{

if
(this_header + count
< next_header)
{

dbmsg();

eat(count);

return 1;

}
else {

dbmsg();

eat(next_header
- this_header);

state = next_state;

return 0;

}

}

1.5 do_reset

write_buffer

--> do_start

--> do_header

--> do_name

--> do_skip

--> do_reset

static
int __init do_reset(void)

{

dbmsg();

while(count
&&
*victim
==
'\0')

eat(1);

if
(count &&
(this_header
& 3))

error("broken padding");

return 1;

}

2.initrd的解压

2.1 initrd的起始地址的获取

make menuconfig中

General setup --->

[*] Initial RAM filesystem and RAM disk (initramfs/initrd) support

start_kernel

-->setup_arch

在arch/arm/kernel/setup.c中

void __init setup_arch(char
**cmdline_p)

{

struct machine_desc
*mdesc;

mdesc = setup_machine_fdt(__atags_pointer);

if
(!mdesc)

mdesc = setup_machine_tags(machine_arch_type); //读取内核参数

//uboot的参数: init=/init initrd=0x62000000,0x00130000

//指定了initrd在内存的起始地址0x62000000,长度0x130000

parse_early_param();

arm_memblock_init(&meminfo, mdesc);
//将物理地址转为虚地址

}

start_kernel

-->setup_arch

--> arm_memblock_init

在arch/arm/mm/init.c中

void __init arm_memblock_init(struct meminfo
*mi, struct machine_desc
*mdesc)

{

#ifdef CONFIG_BLK_DEV_INITRD

if
(phys_initrd_size)
{

memblock_reserve(phys_initrd_start, phys_initrd_size);

initrd_start
= __phys_to_virt(phys_initrd_start);
//将物理地址0x62000000转为虚地址

initrd_end
= initrd_start + phys_initrd_size;
//end地址+size=0x00130000

}

#endif

}

unpack_to_rootfs((char
*)initrd_start, initrd_end
- initrd_start);

其中initrd_start是uboot传入的参数0x62000000的虚地址

里面的内容是烧入板子的boot.img去掉头8字节与尾4个字节,即out/target/product/rk3188/ramdisk.img

注: boot.img的生成

目录out/target/product/rk30sdk/root存在

a.将root下的每个文件加上cpio头+每个文件的内容,打包成cpios格式

b. 将这个cpio文件用gzip压缩后写到文件ramdisk.img中

c. mkkrnlimg会对ramdisk.img加上8个字节的头标志,尾部加上4个字节

2.2 解压并释放initrd中的文件目录

rootfs_initcall(populate_rootfs);

--> populate_rootfs

--> unpack_to_rootfs

在init/initramfs.c中

static char
* __init unpack_to_rootfs(char
*buf, unsigned
len)

{

int i;

int written, res;

decompress_fn decompress;

const char
*compress_name;

static __initdata char msg_buf[64];

header_buf
= kmalloc(110, GFP_KERNEL);

symlink_buf
= kmalloc(PATH_MAX
+ N_ALIGN(PATH_MAX)
+ 1, GFP_KERNEL);

name_buf = kmalloc(N_ALIGN(PATH_MAX),
GFP_KERNEL);

if
(!header_buf
||
!symlink_buf ||
!name_buf)

panic("can't allocate buffers");

state = Start;

this_header
= 0;

message =
NULL;

while
(!message
&&
len)
{

loff_t saved_offset
= this_header;

if
(*buf
==
'0'
&&
!(this_header
& 3))
{

//不是cpio格式,zip压缩过的开头不为字符'0'

continue;

}

this_header
= 0;

//以开头的0x1f, 0x8b判断是zip压缩的,找到gunzip

decompress
= decompress_method(buf,
len,
&compress_name);


//调用压缩函数进行解压缩,解压后调用flush_buffer拷贝到各个目录

decompress(buf,
len,
NULL, flush_buffer,
NULL,
&my_inptr,
error);

this_header
= saved_offset + my_inptr;

buf += my_inptr;

len
-= my_inptr;

}

dir_utime();

kfree(name_buf);

kfree(symlink_buf);

kfree(header_buf);

return message;

}

do_start

do_header

do_name

do_copy

do_utime

do_skip

do_reset

这儿的wite_buffer,比initramfs的write_buffer多了一个do_copy的过程

因为initramfs中只有名,没有数据.initrd有数据,所以需要将数据复制过去.

static
int __init flush_buffer(void
*bufv, unsigned
len)

{

char *buf
= (char
*) bufv;

int written;

int origLen
= len;

if
(message)

return
-1;

while
((written
= write_buffer(buf,
len))
< len
&&
!message)
{

char c
= buf[written];

if
(c ==
'0')
{

buf
+= written;

len
-= written;

state
= Start;

}
else if
(c == 0)
{

buf
+= written;

len
-= written;

state
= Reset;

}
else

error("junk in compressed archive");

}

return origLen;

}