HowToAddFiles < DULG

%SECTION0{name=HowToAddFiles}% How to Add Files to a SELF Ramdisk

It is not always necessary to rebuild a SELF based ramdisk image if you want to modify or to extend it. Especially during development it is often eaiser to unpack it, modify it, and re-pack it again. To do so, you have to understand the internal structure of the =uRamdisk= (resp. =pRamdisk=) images files as used with the U-Boot
(old: <nop>PPCBoot) boot loader:

The =uRamdisk= image contains two parts:

   * a 64 byte U-Boot header
   * a (usually =gzip= compressed) ramdisk image

To modify the contents you have to extract, uncompress and mount the ramdisk image. This can be done as follows:

   1 Extract compressed ramdisk image (=ramdisk.gz=)
      <verbatim>
bash$ dd if=uRamdisk bs=64 skip=1 of=ramdisk.gz
21876+1 records in
21876+1 records out
      </verbatim>
   1 Uncompress ramdisk image (if it was a compressed one)
      <verbatim>
bash$ gunzip -v ramdisk.gz
ramdisk.gz:      66.6% -- replaced with ramdisk
      </verbatim>
   1 Mount ramdisk image
      <verbatim>
bash# mount -o loop ramdisk /mnt/tmp
      </verbatim>

Now you can add, remove, or modify files in the =/mnt/tmp= directory. If you are done, you can re-pack the ramdisk into a U-Boot image:

   1 Unmount ramdisk image:
      <verbatim>
bash# umount /mnt/tmp
      </verbatim>
   1 Compress ramdisk image
      <verbatim>
bash$ gzip -v9 ramdisk
ramdisk:         66.6% -- replaced with ramdisk.gz
      </verbatim>
   1 Create new U-Boot image (=new-uRamdisk=)
      <verbatim>
bash$ mkimage -T ramdisk -C gzip -n 'Simple Embedded Linux Framework' \
> -d ramdisk.gz new-uRamdisk
Image Name:   Simple Embedded Linux Framework
Created:      Sun May  4 13:23:48 2003
Image Type:   PowerPC Linux RAMDisk Image (gzip compressed)
Data Size:    1400121 Bytes = 1367.31 kB = 1.34 MB
Load Address: 0x00000000
Entry Point:  0x00000000
      </verbatim>

Instead of re-packing into a U-boot ramdisk image you can of course also just extract the contents of the SELF image and re-use it as base of a (known to be working) root filesystem.

   * For example, you can create a JFFS2 filesystem using the =mkfs.jffs2= command that comes with the [[MTD Tools]]:
%IF{ %BIG_ENDIAN% eq "true" }%
      <verbatim>
bash# mkfs.jffs2 -r /mnt/tmp -e 0x10000 -o image.jffs2 -b
      </verbatim>
%ELSE%
      <verbatim>
bash# mkfs.jffs2 -r /mnt/tmp -e 0x10000 -o image.jffs2
      </verbatim>
%ENDIF%

   * Or you can create a <nop>CramFS filesystem with =mkcramfs=:
      <verbatim>
bash# mkcramfs -r /mnt/tmp image.cramfs
Swapping filesystem endian-ness
...
Everything: 1656 kilobytes
Super block: 76 bytes
CRC: 7f34cae4
      </verbatim>
14.4. Self		1. Abstract		14.4.2. How to Increase the Size of the Ramdisk
Prev		Home		Next