Busybox与根文件系统的构造

 

嵌入式linux系统的构成

0 确认交叉编译环境已经设置好，我的为arm-linux-

 

1 编译安装Busybox

[root@localhost busybox]# cd /root/embed-2010/embedded-xmu/tools/busybox/

[root@localhost busybox]# make menuconfig

// 以下设置是我自己的设置情况，仅供参考

// 详细设置参考 实验文档Lab3[1].linux+内核裁减及文件系统构建.pdf 附录二

Busybox Settings -->

Build Options -->

 

编译成静态库

跨平台编译 arm-linux-

 

Coreutils -->

 

Init Utilities -->

Linux System Utilities -->

 

Shells -->

 

保存退出

[root@localhost busybox]# make

[root@localhost busybox]# make install PREFIX=/root/embed-2010/embedded-dev/fs

 

2 构建根文件系统

[root@localhost busybox]# cd /root/embed-2010/embedded-dev/fs

[root@localhost fs]# ls

bin  linuxrc  sbin  usr

[root@localhost fs]# mkdir etc dev proc tmp lib var sys

[root@localhost fs]# ls

bin  dev  etc  lib  linuxrc  proc  sbin  sys  tmp  usr  var

创建设备节点

[root@localhost fs]# cd dev/

[root@localhost dev]# mknod ram0 b 1 0

[root@localhost dev]# mknod console c 5 1

[root@localhost dev]# mknod null c 1 3

[root@localhost dev]# mknod zero c 1 5

NOTE:

摘自：http://linux.about.com/library/cmd/blcmdl1_mknod.htm

mknod - make block or character special files  

mknod [OPTION]... NAME TYPE [MAJOR MINOR]  

                                          类型  主    次 设备号

b

create a block (buffered) special file

c, u

create a character (unbuffered) special file

mknod console c 5 1
console为设备文件名，自己随便取
c是指字符型设备 (可选b，块设备)
5是主设备号 /dev/devices里面记录现有的设备
找个没有用的就可以了
1是次设备号，当你要给两个同样的设备上一个驱动的时候就要分了，从0开始，1就是第二个了

Definition:

/dev/null: On UNIX, this is a virtual-file that can be written to. Data written to this file gets discarded.

/dev/zero is a special file that provides as many null characters (ASCII NUL, 0x00) as are read from it.

设备文件：对于每种硬件设备，系统内核有相应的设备驱动程序负责对它的处理。而在Unix中，使用设备文件的方式来表示硬件设备，每种设备驱动程序都被抽象为设备文件的形式，这样就给应用程序一个一致的文件界面，方便应用程序和操作系统之间的通信。

[root@localhost dev]# ls

console  null  ram0  zero

创建inittab P134, inittab 是init程序读取的配置文件。Init是内核启动后运行的第一个程序。

[root@localhost dev]# cd ..

[root@localhost fs]# ls

bin  dev  etc  lib  linuxrc  proc  sbin  sys  tmp  usr  var

[root@localhost fs]# cd etc/

[root@localhost etc]# vim inittab

::sysinit:/etc/init.d/rcS     # 系统初始化时执行的内容

::askfirst:/bin/ash    # 启动shell

建立sysinit（执行指定的程序进行系统初始化）动作项 执行的命令脚本

[root@localhost etc]# mkdir init.d

[root@localhost etc]# vim init.d/rcS

#!/bin/ash

mount -t proc proc/proc

mount -t sysfs sysfs/sys

ifconfig lo 127.0.0.1

ifconfig eth0 192.168.0.100

[root@localhost etc]# chmod +x init.d/rcS

 

3 创建根文件系统映像文件

[root@localhost etc]# cd ../../

[root@localhost embedded-dev]# ls

fs

[root@localhost embedded-dev]# mkdir initrd

[root@localhost embedded-dev]# cd initrd/

[root@localhost initrd]# dd if=/dev/zero of=initrd bs=1k count=2048

读入了 2048+0 个块

输出了 2048+0 个块

NOTE:这将以1024字节为单位，从/dev/zero读取2048字节的数据null characters (ASCII NUL, 0x00)，保存到名字为initrd的文件中，

[root@localhost initrd]# mkfs.ext2 initrd -F

mke2fs 1.32 (09-Nov-2002)

Filesystem label=

OS type: Linux

Block size=1024 (log=0)

Fragment size=1024 (log=0)

256 inodes, 2048 blocks

102 blocks (4.98%) reserved for the super user

First data block=1

1 block group

8192 blocks per group, 8192 fragments per group

256 inodes per group

 

Writing inode tables: done

Writing superblocks and filesystem accounting information: done

 

This filesystem will be automatically checked every 22 mounts or

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

NOTE:

摘自 http://linux.die.net/man/8/mkfs http://linux.die.net/man/8/mkfs.ext2

mkfs - build a Linux file system

In actuality, mkfs is simply a front-end for the various file system builders (mkfs.fstype) available under Linux.

-F

Force mke2fs to run, even if the specified device is not a block special device, or appears to be mounted.

 

[root@localhost initrd]# mkdir initrd_mnt

[root@localhost initrd]# mount initrd initrd_mnt -o loop

NOTE:

摘自：http://www.csulb.edu/~pnguye11/loopbackDev.html

Loopback Devices in Linux

Purpose

The purpose for using a loopback device is to fake out some piece of software so that you can "mount" a file as a disk and read the filesystem in it; the thing that the loopback device points to does not have to be a separate drive, but it can be a file! Once you mount your blank file, you can store individual files in it, and even copy it to a new volume, instantly filling that volume with the directory tree and all that it contains!

-o

Options are specified with a -o flag followed by a comma separated string of options. Some of these options are only useful when they appear in the /etc/fstab file. The following options apply to any file system that is being mounted (but not every file system actually honors them - e.g., the sync option today has effect only for ext2, ext3, fat, vfat and ufs):

摘自： http://linux.die.net/man/8/mount

the Loop Device

One further possible type is a mount via the loop device. For example, the command

mount /tmp/fdimage /mnt -t msdos -o loop=/dev/loop3,blocksize=1024

will set up the loop device /dev/loop3 to correspond to the file /tmp/fdimage, and then mount this device on /mnt.

This type of mount knows about three options, namely loop, offset and encryption, that are really options to losetup(8). (These options can be used in addition to those specific to the filesystem type.)

If no explicit loop device is mentioned (but just an option '-o loop' is given), then mount will try to find some unused loop device and use that. If you are not so unwise as to make /etc/mtab a symbolic link to /proc/mounts then any loop device allocated by mount will be freed by umount. You can also free a loop device by hand, using 'losetup -d', see losetup(8).

 

[root@localhost initrd]# cp -a /root/embed-2010/embedded-dev/fs/* initrd_mnt/

[root@localhost initrd]# umount initrd

[root@localhost initrd]# ls

initrd  initrd_mnt

 

4.skyeye上测试根文件系统

[root@localhost skyeyetest]# cp initrd /root/embed-2010/embedded-xmu/skyeyetest/initrd2010

[root@localhost skyeyetest]# cd /root/embed-2010/embedded-xmu/skyeyetest/

[root@localhost skyeyetest]# vim skyeye.conf

mem_bank: map=M, type=RW, addr=0xc1000000, size=0x01000000, file=./initrd2010

[root@localhost skyeyetest]# ./skyeye -e vmlinux-xmu-2010

arch: arm

cpu info: xscale, pxa25x, 69052100, fffffff0, 2

mach info: name pxa_lubbock, mach_init addr 0x807ced0

uart_mod:0, desc_in:, desc_out:

SKYEYE: use xscale mmu ops

Loaded RAM   ./initrd2010

exec file "vmlinux-xmu-2010"'s format is elf32-little.

……….

……….

……….

Starting pid 657, console /dev/console: '/etc/init.d/rcS'

Bummer, could not run '/etc/init.d/rcS': No such file or directory

Bummer, could not run '/etc/init.d/rcS': No such file or directory

 

Please press Enter to activate this console.

Starting pid 658, console /dev/console: '/bin/ash'

 

 

BusyBox v1.2.2 (2010.03.27-09:16+0000) Built-in shell (ash)

Enter 'help' for a list of built-in commands.

 

/bin/ash: can't access tty; job control turned off

# ls

bin         lib         myspace     sys         var

dev         linuxrc     proc        tmp

etc         lost+found  sbin        usr

#

内核运行成功，根文件系统基本正确。

Bummer, could not run '/etc/init.d/rcS': No such file or directory

/bin/ash: can't access tty; job control turned off

这两个还不知道怎么解决。