linux 系统编程学习笔记四

文件系统

ext2文件系统

分区的格式化工具mkfs

文件系统的总体存储布局

boot block(1kb)

block group 0

super block (超级块):描述整个分区的文件系统信息

GDT(块组描述表group descriptor table)：由块组描述符组成

block bitmap(块位图) 用来描述整个块组中哪些块已用哪些块空闲

inode bitmap(inode 位图):本身占一个块，每个bit表示一个inode可用

inode table(inode 表):文件的描述信息存放在inode中，每个文件都有一个

node,一个块组的所有inode组成inode表

一个块组有多少个8kb就分配多少个inode

data blocks(数据块):存放文件的数据

block group 1

block group n

文件系统中存储的最小单位是块(block)

块的大小在格式化时确定，如mke2fs 的-b参数设定的块的大小

yuezhenhua@ubuntu:/home$ ls -l

总用量 12

drwxrwxrwx 4 root root 4096 2012-03-06 17:04 online

drwxrwxrwx 2 root root 4096 2012-02-02 16:06 share

drwxr-xr-x 33 yuezhenhua yuezhenhua 4096 2012-12-10 20:29 yuezheULL

目录的大小都是4096的整倍，因为分区的块大小是4096,

ls -l /dev/

/*xconsole 文件的类型是p 是一个FIFO文件,不在磁盘上保存数据,*/

crw------- 1 root root 0 2012-12-12 20:05 console

/*zero的文件类型是c,表示字符设备文件,代表内核中的一个设备驱动程序，没有数据块

1 主设备号

5 次设备号

*/

crw-rw-rw- 1 root root 1, 5 2012-12-12 20:04 zero

创建符号链接文件

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ touch hello

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ ln -s ./hello halo

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ ls -l

/*符号链接文件halo指向hello,字节数是7,是"./hello"这7个字符*/

wxrwxrwx 1 yuezhenhua yuezhenhua 7 2012-12-12 20:22 halo -> ./hello

-rw-rw-r-- 1 yuezhenhua yuezhenhua 6 2012-12-12 20:21 hello

创建硬链接

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ ln ./hello hello2

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ ls -l

/*第二栏的数字原本是1，现在变2，ls -l第二栏的数字是硬链接数,

表示一个文件在文件系统中有几个名字,可以保存在不同目录的数据块中，

也保存在inode中

*/

-rw-rw-r-- 2 yuezhenhua yuezhenhua 6 2012-12-12 20:21 hello

-rw-rw-r-- 2 yuezhenhua yuezhenhua 6 2012-12-12 20:21 hello2

目录的硬链接数

/*创建目录a*/

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ mkdir a

/*创建子目录b*/

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ mkdir a/b

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ ls -ld a

/*显示结果 */

drwxrwxr-x 3 yuezhenhua yuezhenhua 4096 2012-12-12 20:33 a

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ ls -la a

/*显示结果 目录a的硬链接数是3*/

总用量 12

drwxrwxr-x 3 yuezhenhua yuezhenhua 4096 2012-12-12 20:33 .

drwxrwxr-x 3 yuezhenhua yuezhenhua 4096 2012-12-12 20:33 ..

drwxrwxr-x 2 yuezhenhua yuezhenhua 4096 2012-12-12 20: b

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ ls -la a/b

/*显示结果 b目录的硬链接数是2*/

总用量 8

drwxrwxr-x 2 yuezhenhua yuezhenhua 4096 2012-12-12 20:33 .

drwxrwxr-x 3 yuezhenhua yuezhenhua 4096 2012-12-12 20:3 ..

示例代码：

1 创建一个1MB的文件并清零

/*dd命令把一个文件的一部分拷贝成另一个文件

if 表示输入文件

of 表示输出文件

count 表示拷贝多少次

bs 表示每次拷贝多少字节

*/

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ dd if=/dev/zero of=fs count=256 bs=4k

记录了256+0 的读入

记录了256+0 的写出

1048576字节(1.0 MB)已复制，0.00396396 秒，265 M 秒

2 对fs进行格式化(把这个文件的数据块合起来看成一个1MB在磁盘分区，在这个分区上再划

分块组)

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ mke2fs fs

mke2fs 1.41.14 (22-Dec-2010)

fs is not a block special device.

无论如何也要继续? (y,n) y

文件系统标签=

操作系统:Linux

块大小=1024 (log=0)

分块大小=1024 (log=0)

Stride=0 blocks, Stripe width=0 blocks

128 inodes, 1024 blocks

51 blocks (4.98%) reserved for the super user

第一个数据块=1

Maximum filesystem blocks=1048576

1 block group

8192 blocks per group, 8192 fragments per group

128 inodes per group

正在写入inode表: 完成

Writing superblocks and filesystem accounting information: 完成

This filesystem will be automatically checked every 34 mounts or

180 days, whichever comes first. Use tune2fs -c or -i to override.

查看个块的块组和描述信息

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ dumpe2fs fs

dumpe2fs 1.41.14 (22-Dec-2010)

Filesystem volume name: <none>

Last mounted on: <not available>

Filesystem UUID: 08c37487-bd06-4258-bd25-d8a323914575

Filesystem magic number: 0xEF53

Filesystem revision #: 1 (dynamic)

Filesystem features: ext_attr resize_inode dir_index filetype sparse_super

Filesystem flags: signed_directory_hash

Default mount options: (none)

Filesystem state: clean

Errors behavior: Continue

Filesystem OS type: Linux

Inode count: 128

Block count: 1024

Reserved block count: 51

Free blocks: 986

Free inodes: 117

First block: 1

Block size: 1024 # 块大小

Fragment size: 1024

Reserved GDT blocks: 3

Blocks per group: 8192

Fragments per group: 8192

Inodes per group: 128

Inode blocks per group: 16

Filesystem created: Wed Dec 12 21:03:32 2012

Last mount time: n/a

Last write time: Wed Dec 12 21:03:32 2012

Mount count: 0

Maximum mount count: 34

Last checked: Wed Dec 12 21:03:32 2012

Check interval: 15552000 (6 months)

Next check after: Mon Jun 10 21:03:32 2013

Reserved blocks uid: 0 (user root)

Reserved blocks gid: 0 (group root)

First inode: 11

Inode size: 128

Default directory hash: half_md4

Directory Hash Seed: 7fdbe0d3-0192-4f0f-b269-d7c083b305c8

#第0个块是启动块,所以group 0只占1023个块

Group 0: (Blocks 1-1023)

主 superblock at 1, Group descriptors at 2-2

保留的GDT块位于 3-5

#块位图占一个块

Block bitmap at 6 (+5), Inode bitmap at 7 (+6)

Inode表位于 8-23 (+7)

986 free blocks, 117 free inodes, 2 directories

可用块数: 38-1023

#每8kb分配一个inode

可用inode数: 12-128

常规文件制作而成的文件系统也可以mount到某个目录

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ sudo mount -o loop fs /mnt

[sudo] password for yuezhenhua:

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ cd /mnt/

yuezhenhua@ubuntu:/mnt$ ls

lost+found

yuezhenhua@ubuntu:/mnt$ ls -la

总用量 17

drwxr-xr-x 3 yuezhenhua yuezhenhua 1024 2012-12-12 21:03 .

drwxr-xr-x 25 root root 4096 2012-04-06 12:29 ..

drwx------ 2 root root 12288 2012-12-12 21:03 lost+found

文件系统在格式化之后在根目录下自动生成三个目录

.

..

lost+found 由e2fsck工具使用

.和..表示根目录本身

yuezhenhua@ubuntu:/$ sudo umount /mnt/

查看这个文件系统的所有字节

/*启动块*/

000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

/*超级块*/

000400 80 00 00 00 00 04 00 00 33 00 00 00 da 03 00 00

inode count=128 block count=1024 reserved block=51 free blocks=986

000410 75 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00

000420 00 20 00 00 00 20 00 00 80 00 00 00 00 00 00 00

000430 2c 85 c8 50 01 00 22 00 53 ef 01 00 01 00 00 00

000440 a4 80 c8 50 00 4e ed 00 00 00 00 00 01 00 00 00

000450 00 00 00 00 0b 00 00 00 80 00 00 00 38 00 00 00

000460 02 00 00 00 01 00 00 00 08 c3 74 87 bd 06 42 58

000470 bd 25 d8 a3 23 91 45 75 00 00 00 00 00 00 00 00

000480 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

0004c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 03 00

0004d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

0004e0 00 00 00 00 00 00 00 00 00 00 00 00 7f db e0 d3

0004f0 01 92 4f 0f b2 69 d7 c0 83 b3 05 c8 01 00 00 00

000500 00 00 00 00 00 00 00 00 a4 80 c8 50 00 00 00 00

000510 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

000560 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

000570 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

000800 06 00 00 00 07 00 00 00 08 00 00 00 da 03 75 00

000810 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

000820 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

001800 ff ff ff ff 1f 00 00 00 00 00 00 00 00 00 00 00

001810 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

001870 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 80

001880 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

*

001c00 ff 07 00 00 00 00 00 00 00 00 00 00 00 00 00 00

001c10 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

*

002000 00 00 00 00 00 00 00 00 a4 80 c8 50 a4 80 c8 50

002010 a4 80 c8 50 00 00 00 00 00 00 00 00 00 00 00 00

002020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

/*根目录的inode

st_mode是以八进制表示,包含文件类型、文件权限

*/

002080 ed 41 e8 03 00 04 00 00 ed 83 c8 50 a4 80 c8 50

st_mode=040755

002090 a4 80 c8 50 00 00 00 00 e8 03 03 00 02 00 00 00

0020a0 00 00 00 00 00 00 00 00 18 00 00 00 00 00 00 00

0020b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

002300 80 81 00 00 00 30 04 04 a4 80 c8 50 a4 80 c8 50

002310 a4 80 c8 50 00 00 00 00 00 00 01 00 08 00 00 00

002320 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

002350 00 00 00 00 00 00 00 00 00 00 00 00 25 00 00 00

002360 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

002500 c0 41 00 00 00 30 00 00 a4 80 c8 50 a4 80 c8 50

002510 a4 80 c8 50 00 00 00 00 00 00 02 00 18 00 00 00

002520 00 00 00 00 00 00 00 00 19 00 00 00 1a 00 00 00

002530 1b 00 00 00 1c 00 00 00 1d 00 00 00 1e 00 00 00

002540 1f 00 00 00 20 00 00 00 21 00 00 00 22 00 00 00

002550 23 00 00 00 24 00 00 00 00 00 00 00 00 00 00 00

002560 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

/*根目录的数据块*/

006000 02 00 00 00 0c 00 01 02 2e 00 00 00 02 00 00 00

006010 0c 00 02 02 2e 2e 00 00 0b 00 00 00 e8 03 0a 02

006020 6c 6f 73 74 2b 66 6f 75 6e 64 00 00 00 00 00 00

006030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

006400 0b 00 00 00 0c 00 01 02 2e 00 00 00 02 00 00 00

006410 f4 03 02 02 2e 2e 00 00 00 00 00 00 00 00 00 00

006420 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

006800 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

006810 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

006c00 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

006c10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

007000 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

007010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

007400 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

007410 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

007800 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

007810 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

007c00 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

007c10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

008000 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

008010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

008400 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

008410 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

008800 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

008810 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

008c00 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

008c10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

009000 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00

009010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

009400 00 00 00 00 03 00 00 00 04 00 00 00 05 00 00 00

009410 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

*

100000

debugfs 可以对文件系统作各种操作,如查看信息、恢复数据、修正文件系统中的错误

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$ debugfs fs

debugfs 1.41.14 (22-Dec-2010)

debugfs: help

显示目录的inode信息

yuezhenhua@ubuntu:/opt/sdk/tc/mmap$stat /

Inode: 2 Type: directory Mode: 0755 Flags: 0x0

Generation: 0 Version: 0x00000000

User: 1000 Group: 1000 Size: 1024

File ACL: 0 Directory ACL: 0

Links: 3 Blockcount: 2

Fragment: Address: 0 Number: 0 Size: 0

ctime: 0x50c880a4 -- Wed Dec 12 21:03:32 2012

atime: 0x50c883ed -- Wed Dec 12 21:17:33 2012

mtime: 0x50c880a4 -- Wed Dec 12 21:03:32 2012

BLOCKS:

(0):24

TOTAL: 1

quit退出debugfs

数据块寻址

如果一个文件有多个数据块，这些数据块可能不是边续存放，需通过其inode中的

索引项blockss查找

文件和目录操作的系统函数

stat(2)读取文件的inode，把inode中和文件属性填入一个struct_stat结构体中返回

示例代码：

stat /opt/file

查找的顺序是

读出inode中的第二项（根目录的inode），找出根目录数据块的位置

从根目录数据块中找出文件名为opt的记录,从记录中读出它的inode号

读出opt目录的inode，找出它数据块的位置

从opt目录的数据块中找出文件名为file的记录,从记录中读出它的inode号

读出file文件的inode

fstat(2)

传入一个文件描述符，传出inode信息

lstat(2)

传入路径，传出inode信息(如果文件是个符号链接文件时，返回的是文件本身的inode)

access(2) 检查执行当前进程的用户是否有权限访问某个文件

传入文件路径和要执行的访问操作（读、写、执行）,取出inode中的st_mode字段,

比较访问权限，0表示允许，-1表示不允许

chmod(2)\fchmod(2) 改变文件的访问权限,修改inode中的st_mode

两函数的区别类似于stat/fstat

chmod(1)命令

chown(2)\fchown(2)\lchown(2) 改变文件的所有者和组,修改inode中的user和group字段

chwn(1)命令

utime改变文件的访问时间和修改时间,修改inode中的atime和mtime字段

touch(1)命令

truncate(2)\ftruncate(2)把文件截断成某个长度,如果新的长度比原长度长，则补0

修改inode中的block索引项和块位图中相应的bit

link(2)创建硬链接,在目录的数据块中添加一条新记录

syslink(2)创建一个符号链接,创建一个新的inode，st_mode的文件类型是符号链接

ln(1) 命令

unlink(2)删除一个链接

符号链接 释放inode和数据块，清除inode位图和块位图中相应的位

硬链接于 清除一条文件名记录

unlink(1)\rm(1)命令

rename(2)改变文件名,修改目录数据块中的文件名记录

mv(1)命令

readlink(2) 读取一个符号链接所指向的目标路径,从符号链接的inode或数据块中读出

目标路径

mkdir(2) 创建一个目录

在父目录的数据块中添加一条记录，分配新的inode和数据块.

mkdir(1)命令

rmdir(2) 删除一个目录(目录必需为空)

释放inode和数据块，清除inode位图和块位图中相应的位,

清除父目录数据块中的记录,父目录的硬链接数减1

rmdir(1)命令

opendir(3)\readdir(3)\close(3)遍历目录数据块中的记录

opendir打开一个目录，返回一个DIR *,类似于file *的名柄

closedir 关闭这个句柄,把dir *指针传给readdir读取目录数据块中的记录

每次返回一个指向struts_dirent的指针

structs_dirent结构体的定义如下

struct dirent{

ino_t d_ino; /*incode number*/

off_t d_off; /*offset to the next dirent*/

unsigned short d_reclen; /*length of this record*/

unsigned char d_type; /*type of file*/

char d_name; /*filename*/

};

用递归打印目录下的所有子目录和文件

#include <sys/types.h>

#include <sys/stat.h>

#include <unistd.h>

#include <dirent.h>

#include <stdio.h>

#include <string.h>

#define MAX_PATH 1024

/*打印目录下的所有子目录和文件*/

void dirwalk(char *dir,void (*fcn)(char *)){

char name[MAX_PATH];

struct dirent *dp;

DIR *dfd;

if((dfd=opendir(dir))==NULL){

fprintf(stderr,"dirwalk: can't open %s\n",dir);

return;

}

while((dp=readdir(dfd))!=NULL){

if(strcmp(dp->d_name,".")==0||strcmp(dp->d_name,"..")==0){

continue;

}

if(strlen(dir)+strlen(dp->d_name)+2>sizeof(name)){

fprintf(stderr,"dirwalk:name %s %s too long\n",dir,dp-

>d_name);

}else{

sprintf(name,"%s%s",dir,dp->d_name);

(*fcn)(name);

}

}

closedir(dfd);

}

void fsize(char *name){

struct stat stbuf;

if(stat(name,&stbuf)==-1){

fprintf(stderr,"fsize: can't access %s\n",name);

return;

}

if((stbuf.st_mode & S_IFMT)==S_IFDIR){

dirwalk(name,fsize);

}

printf("%8ld %s\n",stbuf.st_size,name);

}

int main(int argc,char **argv){

if(argc==1){

fsize(".");

}else{

while(--argc>0){

fsize(*++argv);

}

}

return 0;

}