挂载system.img并提取文件

今天提取线刷包的system.img出来，使用Mount命令挂载

$ sudo mount -t ext4 -o loop system.img /mnt
mount: 文件系统类型错误、选项错误、/dev/loop0 上有坏超级块、
       缺少代码页或助手程序，或其他错误

       有些情况下在 syslog 中可以找到一些有用信息- 请尝试
       dmesg | tail  这样的命令看看。

这坑爹死了。。于是想了个办法把ext4转为yaffs2格式，使用simg2img.py，脚本在博文最下面

$ ./simg2img.py system.img

等待转换完成，当前目录下就会出现一个tmp.img，然后我们就可以挂载了！

$ mkdir tmp
$ sudo mount tmp.img tmp

我需要提取system.img里面文件，所以复制一份出来，然后卸载tmp.img的挂载

$ sudo cp -r tmp system
$ sudo umount tmp

最后递归修改提取出来的文件用户就可以了！

$ sudo chown -R michellgaby system

这样就大功告成了！！下面是ext4转换为yaffs2的脚本

#!/usr/bin/env python
#encoding:utf8
#===============================================================================
#
#          FILE:  simg2img.py
# 
#         USAGE:  ./simg2img.py system.img 
# 
#   DESCRIPTION:  
# 
#        AUTHOR: Karl Zheng 
#       COMPANY: Meizu
#       CREATED: 2011年10月18日 15时25分15秒 CST
#      REVISION:  ---
#===============================================================================

import sys
import struct

class ext4_file_header:
    def __init__(self, buf):
        self.magic, 
                self.major, 
                self.minor, 
                self.file_header_size, 
                self.chunk_header_size, 
                self.block_size, 
                self.total_blocks, 
                self.total_chunks, 
                self.crc32, 
                = struct.unpack('<IHHHHIIII', buf)

class ext4_chunk_header:
    def __init__(self, buf):
        self.type,
                self.reserved,
                self.chunk_size,
                self.total_size,
                = struct.unpack('<HHII', buf)

if len(sys.argv) > 1:
    filename = sys.argv[1]
else:
    print "No file is designated!!"
    sys.exit(1)
ifd = open(filename, "rb")

buf=""

# get filelen
ifd.seek(0, 2)
file_len = ifd.tell()
print file_len
ifd.seek(0, 0)

buf = ifd.read(28)
#print repr(buf)
file_header = ext4_file_header(buf)

EXT4_FILE_HEADER_MAGIC = 0xED26FF3A
EXT4_CHUNK_HEADER_SIZE = 12

if file_header.magic != EXT4_FILE_HEADER_MAGIC:
    print "Not a compressed ext4 file!!"
    sys.exit(1)

print "file_header chunks:%X"%(file_header.total_chunks)

total_chunks = file_header.total_chunks
print("total chunk = %d "%(total_chunks))

ofd = open("tmp.img", "wb")

sector_base = 82528
output_len = 0

while total_chunks > 0:
    buf = ifd.read(EXT4_CHUNK_HEADER_SIZE)
    chunk_header = ext4_chunk_header(buf)
    sector_size = (chunk_header.chunk_size * file_header.block_size) >> 9;
    #print "ct:%X, cs:%X, ts:%X, ss:%X"%(chunk_header.type, chunk_header.chunk_size, chunk_header.total_size, sector_size)

    data = ""
    if chunk_header.type == 0xCAC1:  # raw type 
        data = ifd.read(chunk_header.total_size - EXT4_CHUNK_HEADER_SIZE)
        if len(data) != (sector_size << 9):
            print("len data:%d, sector_size:%d"%(len(data), (sector_size << 9)))
            sys.exit(1)
        else:
            print ("len data:%d, sector_size:%d"%(len(data), sector_size << 9))
            ofd.write(data)
            output_len += len(data)
            print("raw_chunk ")
            print("write raw data in %d size %d 
"%(sector_base, sector_size))
            print("output len:%x"%(output_len))

            sector_base += sector_size
    else:
        if chunk_header.type == 0xCAC2:  # TYPE_FILL
            data = '' * (sector_size << 9);
            ofd.write(data) 
            output_len += len(data)
            print("fill_chunk 
")
            print("chunk_size:%x"%(chunk_header.chunk_size))
            print("output len:%x"%(output_len))
            sector_base += sector_size
        else:
            if chunk_header.type == 0xCAC3:  # TYPE_DONT_CARE
                print "none chunk at chunk:%d"%(file_header.total_chunks - total_chunks)
                print("data_size:0x%x, chunk_size:%d, block_size:%d"%(sector_size << 9, chunk_header.chunk_size, file_header.block_size))
                data = '' * (sector_size << 9);
                ofd.write(data) 
                output_len += len(data)
                sector_base += sector_size
            else:
                data = '' * (sector_size << 9);
                ofd.write(data)
                print "unknown type!!"
                output_len += len(data)
                print("output len:%x"%(output_len))
                sector_base += sector_size

    total_chunks -= 1 
    print("remain chunks = %d "%(total_chunks));

print "write done"

ifd.close()
ofd.close()