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1.瞭解initramfs檔案系統

initramfs在編譯核心的同時被編譯並與核心生成一個映像檔案，可以壓縮也可以不壓縮，但是目前只支援cpio包格式。它是根檔案系統製作和製作的一種非常簡單的方法，也可以通過執行這個檔案系統中的程式引導真正的檔案系統，這樣載入根檔案系統的工作就不是核心的工作，而是initramfs的工作。由於initramfs使用cpio包格式，所以很容易將一個單一的檔案、目錄、node編譯連結到系統中去，這樣很簡單的系統中使用起來很方便，不需要另外掛接檔案系統。

2.對根檔案系統進行修改

[[email protected] rootfs]$ ln -s bin/busybox init

[[email protected] rootfs]$ ll

total 60

drwxr-xr-x 2 lingyun trainning 4096 Apr 25 20:15 apps

drwxr-xr-x 2 lingyun trainning 4096 Apr 26 15:16 bin

drwxr-xr-x 2 lingyun trainning 4096 Apr 25 20:15 data

drwxr-xr-x 2 lingyun trainning 4096 Apr 25 20:51 dev

drwxr-xr-x 4 lingyun trainning 4096 Apr 26 14:16 etc

drwxr-xr-x 2 lingyun trainning 4096 Apr 25 20:15 info

lrwxrwxrwx 1 lingyun trainning   11 Apr 27 21:19 init -> bin/busybox

drwxr-xr-x 3 lingyun trainning 4096 Apr 25 21:17 lib

lrwxrwxrwx 1 root    root        11 Apr 26 15:16 linuxrc -> bin/busybox

drwxr-xr-x 6 lingyun trainning 4096 Apr 25 20:15 mnt

drwxr-xr-x 2 lingyun trainning 4096 Apr 25 20:15 proc

drwxr-xr-x 2 lingyun trainning 4096 Apr 25 20:15 root

drwxr-xr-x 2 lingyun trainning 4096 Apr 26 15:16 sbin

drwxr-xr-x 2 lingyun trainning 4096 Apr 25 20:15 sys

drwxr-xr-x 2 lingyun trainning 4096 Apr 25 20:15 tmp

drwxr-xr-x 6 lingyun trainning 4096 Apr 25 20:15 usr

drwxr-xr-x 2 lingyun trainning 4096 Apr 25 20:57 var

3. 新增核心對initramfs的支援

[[email protected] kernel]$ ls

linux-3.0  linux-3.0.tar.bz2

[[email protected] kernel]$ cd linux-3.0

[[email protected] linux-3.0]$ export TERM=vt100

[[email protected] linux-3.0]$ make menuconfig

。 。 。 。 。 。

General setup  --->
[*] Initial RAM filesystem and RAM disk (initramfs/initrd) support
(/home/hongfuhao/fl2440/rootfs/rootfs) Initramfs source file(s)   #輸入根檔案系統的所在目錄 

。 。 。 。 。 。

[[email protected] linux-3.0]$ ls

arch           fs       linuxrom-s3c2440.bin  README          usr

block          include  MAINTAINERS           REPORTING-BUGS  virt

COPYING        init     Makefile              samples         vmlinux

CREDITS        ipc      mm                    scripts         vmlinux.o

crypto         Kbuild   modules.builtin       security

Documentation  Kconfig  modules.order         sound

drivers        kernel   Module.symvers        System.map

firmware       lib      net                   tools

[[email protected] linux-3.0]$ du -h  linuxrom-s3c2440.bin

6.8M    linuxrom-s3c2440.bin

4.製作映像檔案

5.新增uboot對initramfs支援

U-Boot 2010.09 (Jul 15 2016 - 21:57:32)


DRAM:  64 MiB
NAND:  256 MiB
In:    serial
Out:   serial
Err:   serial
Net:   dm9000
Hit any key to stop autoboot:  0 
[[email protected]]#  set bkr 'tftp 30008000 linuxrom-s3c2440.bin;nand erase 100000 8000000;nand write 30008000 100000 800000'
[[email protected]]# set bootcmd_initramdisk 'nand read 30008000 100000 800000;bootm 30008000'
[[email protected]]# set bootargs 'console=ttyS0,115200 mem=64M init=/linuxrc rw loglevel=7'
[[email protected]]#  set bootcmd 'run bootcmd_initramdisk'
[[email protected]]# save
Saving Environment to NAND...
Erasing Nand...
Erasing at 0x60000 -- 100% complete.
Writing to Nand... done
[[email protected]]# run bkr
dm9000 i/o: 0x20000300, id: 0x90000a46 
DM9000: running in 16 bit mode
MAC: 08:00:3e:26:0a:5b
could not establish link
Using dm9000 device
TFTP from server 192.168.1.2; our IP address is 192.168.1.168
Filename 'linuxrom-s3c2440.bin'.
Load address: 0x30008000
Loading: T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T 
Retry count exceeded; starting again
dm9000 i/o: 0x20000300, id: 0x90000a46 
DM9000: running in 16 bit mode
MAC: 08:00:3e:26:0a:5b
could not establish link
Using dm9000 device
TFTP from server 192.168.1.2; our IP address is 192.168.1.168
Filename 'linuxrom-s3c2440.bin'.
Load address: 0x30008000
Loading: T T T T T T T T T T T T T T #################################################################
         #################################################################
         #################################################################
         #################################################################
         #################################################################
         ##
done
Bytes transferred = 4797912 (4935d8 hex)


NAND erase: device 0 offset 0x100000, size 0x8000000
Skipping bad block at  0x00700000                                          
Skipping bad block at  0x053a0000                                          
Erasing at 0x80e0000 -- 100% complete.
OK


NAND write: device 0 offset 0x100000, size 0x800000
Skip bad block 0x00700000
 8388608 bytes written: OK

6. 啟動引導

[[email protected]]# boot

啟動過程省略。。。。