rk3188--4.android用initrd文件系统启动流程



在init/intramfs.c中

1. static int __init populate_rootfs(void)
   
2. {
3.     unpack_to_rootfs(__initramfs_start, __initramfs_size);  //1. initramfs的解压
   
4.     if (initrd_start) {
   
5.         unpack_to_rootfs((char *)initrd_start, initrd_end - initrd_start); //2.initrd的解压
   
6.         free_initrd();
   
7.     }
   
8. }
   
9. 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

1. static char * __init unpack_to_rootfs(char *buf, unsigned len)
   
2. {
   
3.     int i;
   
4.     int written, res;
   
5.     decompress_fn decompress;
   
6.     const char *compress_name;
   
7.     static __initdata char msg_buf[64];
   
8.     header_buf = kmalloc(110, GFP_KERNEL);
   
9.     symlink_buf = kmalloc(PATH_MAX + N_ALIGN(PATH_MAX) + 1, GFP_KERNEL);
   
10.     name_buf = kmalloc(N_ALIGN(PATH_MAX), GFP_KERNEL);
    
11.     state = Start;
    
12.     this_header = 0;
    
13.     message = NULL;
    
14.     while (!message && len) {
    
15.         loff_t saved_offset = this_header;
16.         //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
    
17.         if (*buf == '0' && !(this_header & 3)) {
    
18.             state = Start;
    
19.             written = write_buffer(buf, len);
    
20.             buf += written;
    
21.             len -= written;
    
22.             continue;
    
23.         }       
    
24.     }
    
25.     dir_utime();
    
26.     kfree(name_buf);
    
27.     kfree(symlink_buf);
    
28.     kfree(header_buf);
    
29.     return message;
    
30. }

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

1. dir /dev 0755 0 0
   
2. nod /dev/console 0600 0 0 c 5 1
   
3. 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

1. static int __init write_buffer(char *buf, unsigned len)
   
2. {
   
3.     count = len;
   
4.     victim = buf;
   
5. 
   
6.     while (!actions[state]())
   
7.         ;
   
8.     return len - count;
   
9. }

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

1. static int __init do_start(void)
   
2. {
3.     //实际作用是将collect指针移动到打包的cpio每一个文件头处
   
4.     read_into(header_buf, 110, GotHeader);
   
5.     return 0;
   
6. }

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

1. static void __init read_into(char *buf, unsigned size, enum state next)
   
2. {
   
3.     if (count >= size) {
   
4.         collected = victim;
   
5.         eat(size);
   
6.         state = next;      //下一步要执行do_header
   
7.     }
8. }

1.2 do_header解析110字节的头
write_buffer
    --> do_start
        --> do_header

1. static int __init do_header(void)
   
2. {
   
3.     if (memcmp(collected, "070707", 6)==0) {
   
4.         error("incorrect cpio method used: use -H newc option");
   
5.         return 1;
   
6.     }
   
7.     if (memcmp(collected, "070701", 6)) {
   
8.         error("no cpio magic");
   
9.         return 1;
   
10.     }
    
11.     parse_header(collected);      //从101个字节的头中解析出inod mode uid gid等
    
12.     next_header = this_header + N_ALIGN(name_len) + body_len;   //移到下一个文件的头处
    
13.     next_header = (next_header + 3) & ~3;              //cpio的头部都是4字节对齐的
    
14.     state = SkipIt;
    
15.     if (name_len <= 0 || name_len > PATH_MAX)
    
16.         return 0;
    
17.     if (S_ISLNK(mode)) {
    
18.         if (body_len > PATH_MAX)
    
19.             return 0;
    
20.         collect = collected = symlink_buf;
    
21.         remains = N_ALIGN(name_len) + body_len;
    
22.         next_state = GotSymlink;
    
23.         state = Collect;
    
24.         return 0;
    
25.     }
26.     //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
27.     //所以这儿代表的是,所有非链接文件
    
28.     if (S_ISREG(mode) || !body_len)                 
    
29.         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
    
30.     return 0;                                             //并将状态改为GotName,即要调用do_name
    
31. }

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.

1. static int __init do_name(void)
   
2. {
   
3.     state = SkipIt;
   
4.     next_state = Reset;
   
5.     if (strcmp(collected, "TRAILER!!!") == 0) {   //判断是不是结尾
   
6.         free_hash();
   
7.         return 0;
   
8.     }
   
9.     clean_path(collected, mode);         //把原先有的路径去掉, 相当于rmdir /dev 或 rm /dev/console
   
10.     if (S_ISREG(mode)) {                        
    
11.         int ml = maybe_link();
    
12.         if (ml >= 0) {
    
13.             int openflags = O_WRONLY|O_CREAT;
    
14.             if (ml != 1)
    
15.                 openflags |= O_TRUNC;
    
16.             wfd = sys_open(collected, openflags, mode);    //如果是普通文件打开sys_open
    
17. 
    
18.             if (wfd >= 0) {
    
19.                 sys_fchown(wfd, uid, gid);                 //设置权限等
    
20.                 sys_fchmod(wfd, mode);
    
21.                 if (body_len)
    
22.                     sys_ftruncate(wfd, body_len);
    
23.                 vcollected = kstrdup(collected, GFP_KERNEL);
    
24.                 state = CopyFile;                         //最后调用do_copy将文件内容复制过来
    
25.             }
    
26.         }
    
27.     } else if (S_ISDIR(mode)) {                      // 以/dev为例
    
28.         sys_mkdir(collected, mode);                  // 创建 /dev目录
    
29.         sys_chown(collected, uid, gid);              // 设置所有者
    
30.         sys_chmod(collected, mode);                  // 设置权限
    
31.         dir_add(collected, mtime);                   // 更改/dev目录的mtime
    
32.     } else if (S_ISBLK(mode) || S_ISCHR(mode) || S_ISFIFO(mode) || S_ISSOCK(mode)) {
    
33.         if (maybe_link() == 0) {                     // 以/dev/console为例 
    
34.             sys_mknod(collected, mode, rdev);        // 创建 /dev/console结点
    
35.             sys_chown(collected, uid, gid);          // 设置所有者
    
36.             sys_chmod(collected, mode);              // 设置权限
    
37.             do_utime(collected, mtime);              // 更改时间戳
    
38.         }
    
39.     }
    
40.     return 0;
    
41. }

1.3 do_skip
write_buffer
    --> do_start
        --> do_header
            --> do_name
                --> do_skip

1. static int __init do_skip(void)
   
2. {
   
3.     if (this_header + count < next_header) {
   
4.         dbmsg();
   
5.         eat(count);
   
6.         return 1;
   
7.     } else {
   
8.         dbmsg();
   
9.         eat(next_header - this_header);
   
10.         state = next_state;
    
11.         return 0;
    
12.     }
    
13. }

1.5 do_reset
write_buffer
    --> do_start
        --> do_header
            --> do_name
                --> do_skip
                    --> do_reset

1. static int __init do_reset(void)
   
2. {
   
3.     dbmsg();
   
4.     while(count && *victim == '\0')
   
5.         eat(1);
   
6.     if (count && (this_header & 3))
   
7.         error("broken padding");
   
8.     return 1;
   
9. }

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

1. void __init setup_arch(char **cmdline_p)
   
2. {
   
3.     struct machine_desc *mdesc;
   
4.     mdesc = setup_machine_fdt(__atags_pointer); 
   
5.     if (!mdesc)
   
6.         mdesc = setup_machine_tags(machine_arch_type);  //读取内核参数
7.     //uboot的参数: init=/init initrd=0x62000000,0x00130000
8.     //指定了initrd在内存的起始地址0x62000000,长度0x130000
   
9.     parse_early_param();  
   
10.     arm_memblock_init(&meminfo, mdesc); //将物理地址转为虚地址
    
11. }

start_kernel
    -->setup_arch
        --> arm_memblock_init
在arch/arm/mm/init.c中

1. void __init arm_memblock_init(struct meminfo *mi, struct machine_desc *mdesc)
   
2. {
   
3. #ifdef CONFIG_BLK_DEV_INITRD
   
4.     if (phys_initrd_size) {
   
5.         memblock_reserve(phys_initrd_start, phys_initrd_size);
   
6.         initrd_start = __phys_to_virt(phys_initrd_start);     //将物理地址0x62000000转为虚地址
   
7.         initrd_end = initrd_start + phys_initrd_size;         //end地址+size=0x00130000  
   
8.     }
   
9. #endif
   
10. }

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

1. static char * __init unpack_to_rootfs(char *buf, unsigned len)
   
2. {
   
3.     int i;
   
4.     int written, res;
   
5.     decompress_fn decompress;
   
6.     const char *compress_name;
   
7.     static __initdata char msg_buf[64];
   
8.     header_buf = kmalloc(110, GFP_KERNEL);
   
9.     symlink_buf = kmalloc(PATH_MAX + N_ALIGN(PATH_MAX) + 1, GFP_KERNEL);
   
10.     name_buf = kmalloc(N_ALIGN(PATH_MAX), GFP_KERNEL);
    
11. 
    
12.     if (!header_buf || !symlink_buf || !name_buf)
    
13.         panic("can't allocate buffers");
    
14. 
    
15.     state = Start;
    
16.     this_header = 0;
    
17.     message = NULL;
    
18.     while (!message && len) {
    
19.         loff_t saved_offset = this_header;
    
20.         if (*buf == '0' && !(this_header & 3)) {
21.             //不是cpio格式,zip压缩过的开头不为字符'0'
    
22.             continue;
    
23.         }
    
24.         this_header = 0;
25.         //以开头的0x1f, 0x8b判断是zip压缩的,找到gunzip
    
26.         decompress = decompress_method(buf, len, &compress_name);
27.         //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
    
28.         decompress(buf, len, NULL, flush_buffer, NULL, &my_inptr, error);       
    
29.         this_header = saved_offset + my_inptr;
    
30.         buf += my_inptr;
    
31.         len -= my_inptr;
    
32.     }
    
33.     dir_utime();
    
34.     kfree(name_buf);
    
35.     kfree(symlink_buf);
    
36.     kfree(header_buf);
    
37.     return message;
    
38. }

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.

1. static int __init flush_buffer(void *bufv, unsigned len)
   
2. {
   
3.     char *buf = (char *) bufv;
   
4.     int written;
   
5.     int origLen = len;
   
6.     if (message)
   
7.         return -1;
   
8.     while ((written = write_buffer(buf, len)) < len && !message) {
   
9.         char c = buf[written];
   
10.         if (c == '0') {
    
11.             buf += written;
    
12.             len -= written;
    
13.             state = Start;
    
14.         } else if (c == 0) {
    
15.             buf += written;
    
16.             len -= written;
    
17.             state = Reset;
    
18.         } else
    
19.             error("junk in compressed archive");
    
20.     }
    
21.     return origLen;
    
22. }