那个网站可以做公示,手机端网站建设要点,西宁市建设网站公司电话,做一个主题的网页代码前言学习文件系统的第一步#xff0c;先搞清楚文件系统在设备上的存储结构#xff0c;先来简单了解一下。F2FS空间布局图和描述选自《F2FS技术拆解》https://mp.weixin.qq.com/s/k1ibtWF_TRQi8wbqUGjMrgF2FS空间布局F2FS空间布局整个存储空间被划分为6个区域#xff1a;超级… 前言学习文件系统的第一步先搞清楚文件系统在设备上的存储结构先来简单了解一下。F2FS空间布局图和描述选自《F2FS技术拆解》https://mp.weixin.qq.com/s/k1ibtWF_TRQi8wbqUGjMrgF2FS空间布局F2FS空间布局整个存储空间被划分为6个区域超级块SB 包含基本分区信息和F2FS在格式化分区时确定不可更改的参数检查点CP 保存文件系统状态有效NAT/SIT见下文说明集合的位图孤儿inode列表文件被删除时尚有引用无法立即释放时需被计入此列表以便再次挂载时释放和当前活跃段的所有者信息。和其他日志结构文件系统一样F2FS检查点时某一给定时点一致的文件系统状态集合——可用于系统崩溃或掉电后的数据恢复。F2FS的两个检查点各占一个Segment和前述不同的是F2FS通过检查点头尾两个数据块中的version信息判断检查点是否有效。段信息表Segment Information TableSIT 包含主区域Main Area见下文说明中每个段的有效块数和标记块是否有效的位图。SIT主要用于回收过程中选择需要搬移的段和识别段中有效数据。索引节点地址表Node Address TableNAT 用于定位所有主区域的索引节点块包括inode节点、直接索引节点、间接索引节点地址。即NAT中存放的是inode或各类索引node的实际存放地址。段摘要区Segment Summary Area (SSA) 主区域所有数据块的所有者信息即反向索引包括父inode号和内部偏移。SSA表项可用于搬移有效块前查找其父亲索引节点编号,主区域 Main Area 由4KB大小的数据块组成每个块被分配用于存储数据文件或目录内容和索引inode或数据块索引。一定数量的连续块组成Segment进而组成Section和Zone如前所述。一个Segment要么存储数据要么存储索引据此可将Segment划分为数据段和索引段。眼见为实耳听为虚我们自己动手实验一样一、创建块设备在sdcard中新建一个100MB大小的文件f2fs_devicedd if/dev/zero of/sdcard/f2fs_device bs1MB count100
将文件f2fs_device格式化成f2fs文件系统make_f2fs /sdcard/f2fs_device
将f2fs_device和loop设备绑定生成一个虚拟块设备如果提示设备忙13换成其他数字losetup /dev/block/loop13 /sdcard/f2fs_device
新建一个目录f2fs_root_dirmkdir /sdcard/f2fs_root_dir
将loop13挂在到f2fs_root_dir目录mount -t f2fs /dev/block/loop13 /sdcard/f2fs_root_dir
二、填充数据在目录中新建一个1.txt文件并且写入hello worldT1_PRO:/sdcard/f2fs_root_dir # touch 1.txt
T1_PRO:/sdcard/f2fs_root_dir # echo hello world 1.txt
三、hexdump工具分析pull出文件f2fs_device千万别出pull f2fs_root_dir这个路径adb pull sdcard/f2fs_device
直接用hexdump分析块设备的原始数据hexdump -C f2fs_device
3.1 dump开头内容分析首先你会看到下面的一堆16进制的数字就是块设备的原始数据00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
#super block 1 start
*
00000400 10 20 f5 f2 01 00 0b 00 09 00 00 00 03 00 00 00 |. ..............|
00000410 0c 00 00 00 09 00 00 00 01 00 00 00 01 00 00 00 |................|
00000420 00 00 00 00 00 64 00 00 00 00 00 00 2a 00 00 00 |.....d......*...|
00000430 31 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 |1...............|
00000440 01 00 00 00 2a 00 00 00 00 02 00 00 00 02 00 00 |....*...........|
00000450 00 06 00 00 00 0a 00 00 00 0e 00 00 00 10 00 00 |................|
00000460 03 00 00 00 01 00 00 00 02 00 00 00 b6 71 aa 9d |.............q..|
00000470 8e e2 40 64 81 df 52 71 22 74 8d ac 00 00 00 00 |..d..Rqt......|
00000480 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000870 00 00 00 00 00 00 00 00 00 00 00 00 22 00 00 00 |...............|
00000880 6a 70 67 00 00 00 00 00 67 69 66 00 00 00 00 00 |jpg.....gif.....|
00000890 70 6e 67 00 00 00 00 00 61 76 69 00 00 00 00 00 |png.....avi.....|
000008a0 64 69 76 78 00 00 00 00 6d 34 61 00 00 00 00 00 |divx....m4a.....|
000008b0 6d 34 76 00 00 00 00 00 6d 34 70 00 00 00 00 00 |m4v.....m4p.....|
000008c0 6d 70 34 00 00 00 00 00 6d 70 33 00 00 00 00 00 |mp4.....mp3.....|
000008d0 33 67 70 00 00 00 00 00 77 6d 76 00 00 00 00 00 |3gp.....wmv.....|
000008e0 77 6d 61 00 00 00 00 00 6d 70 65 67 00 00 00 00 |wma.....mpeg....|
000008f0 6d 6b 76 00 00 00 00 00 6d 6f 76 00 00 00 00 00 |mkv.....mov.....|
00000900 61 73 78 00 00 00 00 00 61 73 66 00 00 00 00 00 |asx.....asf.....|
00000910 77 6d 78 00 00 00 00 00 73 76 69 00 00 00 00 00 |wmx.....svi.....|
00000920 77 76 78 00 00 00 00 00 77 76 00 00 00 00 00 00 |wvx.....wv......|
00000930 77 6d 00 00 00 00 00 00 6d 70 67 00 00 00 00 00 |wm......mpg.....|
00000940 6d 70 65 00 00 00 00 00 72 6d 00 00 00 00 00 00 |mpe.....rm......|
00000950 6f 67 67 00 00 00 00 00 6f 70 75 73 00 00 00 00 |ogg.....opus....|
00000960 66 6c 61 63 00 00 00 00 6a 70 65 67 00 00 00 00 |flac....jpeg....|
00000970 76 69 64 65 6f 00 00 00 61 70 6b 00 00 00 00 00 |video...apk.....|
00000980 73 6f 00 00 00 00 00 00 65 78 65 00 00 00 00 00 |so......exe.....|
00000990 64 62 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |db..............|
000009a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
...省略大量数据
3.1.1 超级块SB超级块SB从0x00000400开始也就是从1KB开始存不是从0开始.存在两个一模一样的超级块SBf2fs的设计防止数据损坏两个结构体间隔4KB00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000400 10 20 f5 f2 01 00 0b 00 09 00 00 00 03 00 00 00 |. ..............|//SB1
*
00001400 10 20 f5 f2 01 00 0b 00 09 00 00 00 03 00 00 00 |. ..............|//SB2
3.1.3 检查点CP检查点CP从0x00200000开始也就是2MB开始因为一个Segment为2MB检查点CP是段对齐的*
00200000 3b 51 5b 23 00 00 00 00 00 28 00 00 00 00 00 00 |;Q[#.....(......|#CP
3.2 文件1.txt整个1.txt文件对应的索引inode从地址0x01201000到0x01202000等于0x1000B 4KB留个疑问为什么文件内容hello world会保存在inode块而不是在数据块01201000 b6 81 00 0b 00 00 00 00 00 00 00 00 01 00 00 00 |................|
01201010 0c 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 |................|
01201020 4f 26 70 5e 00 00 00 00 57 26 70 5e 00 00 00 00 |Op^....Wp^....|
01201030 57 26 70 5e 00 00 00 00 a2 f4 2a 02 9e 08 d3 1d |Wp^......*.....|
01201040 9e 08 d3 1d af 1e c5 19 00 00 00 00 00 00 00 00 |................|
01201050 00 00 00 00 03 00 00 00 05 00 00 00 31 2e 74 78 |............1.tx|
01201060 74 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |t...............|
01201070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
01201160 00 00 00 00 00 00 00 00 00 00 00 00 68 65 6c 6c |............hell|
01201170 6f 20 77 6f 72 6c 64 0a 00 00 00 00 00 00 00 00 |o world.........|
01201180 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
01201f00 00 00 00 00 00 00 00 00 00 00 00 00 11 20 f5 f2 |............. ..|
01201f10 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
01201f20 00 00 00 00 06 07 18 00 73 65 6c 69 6e 75 78 75 |........selinuxu|
01201f30 3a 6f 62 6a 65 63 74 5f 72 3a 75 6e 6c 61 62 65 |:object_r:unlabe|
01201f40 6c 65 64 3a 73 30 00 00 00 00 00 00 00 00 00 00 |led:s0..........|
01201f50 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
01201fe0 00 00 00 00 00 00 00 00 04 00 00 00 04 00 00 00 |................|
01201ff0 01 00 00 00 3a 51 5b 23 21 79 00 61 02 12 00 00 |....:Q[#!y.a....|
01202000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
3.3最后一行最大的寻址是0x06400000100MB我们创建的块设备就是100MB*
06400000
四、dump.f2fs工具分析单纯的用hexdump去分析f2fs块设备上的存储结构我们还可以通过dump.f2fs工具去查看当然Android源码下默认dump.f2fs是关闭的以后我再写文章如何开启Android下的dump.f2fs。4.1 dump.f2fs使用说明Usage: dump.f2fs [options] device
[options]:-d debug level [default:0]-i inode no (hex)-n [NAT dump nid from #1~#2 (decimal), for all 0~-1]-s [SIT dump segno from #1~#2 (decimal), for all 0~-1]-S sparse_mode-a [SSA dump segno from #1~#2 (decimal), for all 0~-1]-b blk_addr (in 4KB)-V print the version number and exit
4.2 dump.f2fs -n触发dump node address table1|T1_PRO:/sdcard $ dump.f2fs -n 0~-1 f2fs_deviceInfo: No support kernel version!
Info: Segments per p 1
Info: Sections per zone 1
Info: sector size 512
Info: total sectors 204800 (100 MB)
Info: MKFS version4.14.117 #1 SMP PREEMPT Mon Mar 9 21:37:48 CST 2020
Info: FSCK versionfrom 4.14.117 #1 SMP PREEMPT Mon Mar 9 21:37:48 CST 2020to 4.14.117 #1 SMP PREEMPT Mon Mar 9 21:37:48 CST 2020
Info: superblock features 0 :
Info: superblock encrypt level 0, salt 00000000000000000000000000000000
Info: total FS sectors 204800 (100 MB)
Info: CKPT version 235b513e
Info: checkpoint state c5 : nat_bits crc compacted_summary unmountDone.
查看生成文件dump_natT1_PRO:/sdcard $ cat dump_nat
nid: 3 ino: 3 offset: 0 blkaddr: 4098 pack:2
nid: 4 ino: 4 offset: 0 blkaddr: 4609 pack:2
注意nid 4对应的blkaddr 4609转成16进制就是1201有没有点眼熟看看3.2 中dump的1.txt的文件对应的inode第一样的地址01201000所以blkaddr:4609就是代表nid为4的数据结构在存储设备中的地址也就是blkaddr * 4k还记得开头说的主区域 Main Area 由4KB大小的数据块组成嘛正好对应。01201000 b6 81 00 0b 00 00 00 00 00 00 00 00 01 00 00 00 |................|
4.3 dump.f2fs -idump inode号对应的inode结构体T1_PRO:/sdcard $ dump.f2fs -i 4 f2fs_deviceInfo: No support kernel version!
Info: Segments per p 1
Info: Sections per zone 1
Info: sector size 512
Info: total sectors 204800 (100 MB)
Info: MKFS version4.14.117 #1 SMP PREEMPT Mon Mar 9 21:37:48 CST 2020
Info: FSCK versionfrom 4.14.117 #1 SMP PREEMPT Mon Mar 9 21:37:48 CST 2020to 4.14.117 #1 SMP PREEMPT Mon Mar 9 21:37:48 CST 2020
Info: superblock features 0 :
Info: superblock encrypt level 0, salt 00000000000000000000000000000000
Info: total FS sectors 204800 (100 MB)
Info: CKPT version 235b513e
[print_node_info: 275] Node ID [0x4:4] is inode
i_mode [0x 81b6 : 33206]
i_advise [0x 0 : 0]
i_uid [0x 0 : 0]
i_gid [0x 0 : 0]
i_links [0x 1 : 1]
i_size [0x c : 12]
i_blocks [0x 1 : 1]
i_atime [0x5e70264f : 1584408143]
i_atime_nsec [0x 22af4a2 : 36369570]
i_ctime [0x5e702657 : 1584408151]
i_ctime_nsec [0x1dd3089e : 500369566]
i_mtime [0x5e702657 : 1584408151]
i_mtime_nsec [0x1dd3089e : 500369566]
i_generation [0x19c51eaf : 432348847]
i_current_depth [0x 0 : 0]
i_xattr_nid [0x 0 : 0]
i_flags [0x 0 : 0]
i_inline [0x b : 11]
i_pino [0x 3 : 3]
i_dir_level [0x 0 : 0]
i_namelen [0x 5 : 5]
i_name [1.txt]
i_ext: fofs:0 blkaddr:0 len:0
i_addr[ofs] [0x 0 : 0]
i_addr[ofs 1] [0x6c6c6568 : 1819043176]
i_addr[ofs 2] [0x6f77206f : 1870078063]
i_addr[ofs 3] [0x a646c72 : 174353522]
i_addr[0x3] points data block [0xa646c72]
i_nid[0] [0x 0 : 0]
i_nid[1] [0x 0 : 0]
i_nid[2] [0x 0 : 0]
i_nid[3] [0x 0 : 0]
i_nid[4] [0x 0 : 0]xattr: e_name_index:6 e_name:selinux e_name_len:7 e_value_size:24 e_value:
753A6F626A6563745F723A756E6C6162656C65643A733000Do you want to dump this file into ./lost_found/? [Y/N] y
Info: checkpoint state c5 : nat_bits crc compacted_summary unmountDone.
如果选择y可以dump出1.txt到./lost_found/路径下似乎这个指令以后可以用来从原始数据直接生成文件Do you want to dump this file into ./lost_found/? [Y/N] y
T1_PRO:/sdcard $ cat ./lost_found/1.txt
hello world
注意inode的i_addr看起来数字是不是也很眼熟其实就是hello world为什么i_addr不是指向数据块而是直接存储hello world。因为F2FS支持inline data数据直接存储在inode中小文件大小最大可达约3.4KB在Android大量小文件场景中对存取空间占用和性能有一定优化。i_addr[ofs 1] [0x6c6c6568 : 1819043176]
i_addr[ofs 2] [0x6f77206f : 1870078063]
i_addr[ofs 3] [0x a646c72 : 174353522]
01201160 00 00 00 00 00 00 00 00 00 00 00 00 68 65 6c 6c |............hell|
01201170 6f 20 77 6f 72 6c 64 0a 00 00 00 00 00 00 00 00 |o world.........|
五、总结对f2fs存储结构学习只有这么一点是远远不够的为什么研究文件系统要先研究存储结构因为文件系统的很多代码都是按照存储结构来写的我觉得文件系统其实就是块设备的原始数据的翻译者管理者。 回复「 篮球的大肚子」进入技术群聊回复「1024」获取1000G学习资料
