Modifying the root image

(Set "Modifying the root image" as the Wiki page of the day)
(Initial cleanup)
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This HOWTO describes 2 methods for extending and modifying an existing JFFS2 root image of 770.
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This article describes two methods for extending and modifying an existing tablet JFFS2 root image.
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=Background =
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== Background ==
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The root filesystem (rootfs) of the Nokia 770 is stored in a Journal Flash File System version 2 (JFFS2) format. It resides on one of the partitions on the flash chip in the Nokia 770. Additionally, a pristine version of the rootfs can be obtained from the [http://tablets-dev.nokia.com/nokia_770.php Nokia official firmware].
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The root filesystem (rootfs) of the tablets is stored in a Journal Flash File System version 2 (JFFS2) format. It resides on one of the partitions on the flash chip in the device. Additionally, a pristine version of the rootfs can be obtained from the [http://tablets-dev.nokia.com/ Nokia official firmware] site.
There are two ways to mount the JFFS2 image:
There are two ways to mount the JFFS2 image:
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#Have kernel memory emulate a MTD via mtdram
#Have kernel memory emulate a MTD via mtdram
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=Getting the JFFS2 Image=
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== Getting the JFFS2 image ==
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First of all, we need to get the rootfs.jffs2 from the official [http://tablets-dev.nokia.com/nokia_770.php Nokia binary]:
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First of all, we need to get the rootfs.jffs2 from the official [http://tablets-dev.nokia.com/ Nokia FIASCO image]. After downloading the FIASCO image, run this on it to unpack it (this will give you all of the individual parts of the image):
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  $ mkdir SE2005_image
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  sudo ./flasher-3.0 --unpack  -F <FIASCO image>
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$ cd SE2005_image
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$ sudo ./flasher --unpack  -F /path_to_file/Nokia_770_SE2005_3_2005_51_13.bin
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Found image 2nd (length 8576)
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== Mounting the JFFS2 image ==
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Found image secondary (length 79360)
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These commands will be executed with root privileges on the host machine and not on the device itself.
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Found image xloader (length 13824)
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Found image initfs (length 1581824)
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Found image kernel (length 1481856)
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Found image rootfs (length 58851328)
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Unpacking 2nd image to file '2nd.bin'...
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Unpacking X-Loader image to file 'xloader.bin'...
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Unpacking secondary image to file 'secondary.bin'...
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Unpacking kernel image to file 'zImage'...
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Unpacking initfs image to file 'initfs.jffs2'...
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Unpacking rootfs image to file 'rootfs.jffs2'...  
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=Mounting JFFS2 Image=
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=== Block device emulating an MTD device ===
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It is assume that all these commands will be executed on the development/hacking host and not on the Nokia 770 itself. Also assumed is all these commands will be executed with root privileges (i.e. sudo /bin/sh).
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You must have the following kernel modules compiled and installed:
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=='''Block Device Emulating a MTD'''==
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==='''Linux 2.4.x Kernel'''===
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If you are using a Linux 2.4.x kernel, you must have the following kernel modules compiled:
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*CONFIG_MTD (mtdcore)
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*CONFIG_MTD_PARITIONS (mtdpart)
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*CONFIG_MTD_MTDRAM (mtdram)
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*CONFIG_MTD_BLKMTD (blkmtd)
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*CONFIG_BLK_DEV_LOOP (loop)
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==='''Linux 2.6.x Kernel'''===
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If you are using a Linux 2.6.x kernel, you must have the following kernel modules compiled:
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*CONFIG_MTD (mtdcore)  
*CONFIG_MTD (mtdcore)  
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  losetup /dev/loop0 rootfs.jffs2
  losetup /dev/loop0 rootfs.jffs2
  modprobe mtdblock
  modprobe mtdblock
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  modprobe blkmtd device=/dev/loop0 ### for Linux 2.4.x
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  modprobe block2mtd
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    or
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echo "/dev/loop0" > /sys/module/block2mtd/parameters/block2mtd
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  modprobe block2mtd ### for Linux 2.6.x
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  echo "/dev/loop0" > /sys/module/block2mtd/parameters/block2mtd ### Linux 2.6.x
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  modprobe jffs2
  modprobe jffs2
  mount -t jffs2 /tmp/mtdblock0 /media/jffs2
  mount -t jffs2 /tmp/mtdblock0 /media/jffs2
Line 71: Line 44:
  umount /media/jffs2
  umount /media/jffs2
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  modprobe -r blkmtd ### Linux 2.4.x
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  modprobe -r block2mtd
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    or
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  modprobe -r block2mtd ## Linux 2.6.x
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  modprobe -r mtdblock
  modprobe -r mtdblock
  losetup -d /dev/loop0
  losetup -d /dev/loop0
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You can use the following Shell script to automate the process.
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=== Kernel memory emulating an MTD device ===
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To mount the JFFS2 image, you perform the following steps:
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==Kernel Memory Emulating a MTD==
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(Idea originally from Michael Mlivoncic) To mount the JFFS2 image, you perform the following steps:
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  mknod /tmp/mtdblock0 b 31 0
  mknod /tmp/mtdblock0 b 31 0
Line 97: Line 66:
  modprobe -r mtdblock
  modprobe -r mtdblock
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You can use the following Shell script to automate the process.
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== Archiving and extracting the rootfs image ==
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The image is now accessible under /media/jffs2. Copy the whole image to another directory. This new directory will be used for modifying the image. Extending the currently mounted JFFS2 image is not suggested. Using cp for copying the image to a working directory won't work due to special files in /media/jffs2/dev, which is why we use tar.  
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=Archiving and Extracting the Root Image=
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cd /media/jffs2
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The image is now accessible under /media/jffs2. Copy the whole image to another directory. This new directory will be used for modifying the image. Extending the currently mounted JFFS2 image is not suggested. Using cp for copying the image to a working directory won't work due to special files in /media/jffs2/dev, for example. This is the reason we use tar. proceed as above, i.e.:
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tar cvzf /my_path/myRootImage.tar.gz .
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cd $HOME
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mkdir myRootImage
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cd myRootImage
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tar xvpzf /my_path/myRootImage.tar.gz
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$ cd /media/jffs2
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== Modifying the copy of the image ==
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$ tar cvzf /my_path/myRootImage.tar.gz .
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Now the image is successfully archived and copied. The working directory $HOME/myRootImage can now be used for adding, changing or modifying packages.
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  $ cd $HOME
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$ mkdir myRootImage
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$ cd myRootImage
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$ tar xvpzf /my_path/myRootImage.tar.gz
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=Modifying the Copy of Image=
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  cd $HOME/myRootImage
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Now the image is successfully archived and copied. The working directory $HOME/myRootImage can now be used for adding packages etc, for example.
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  dpkg -x $HOME/arm_debs/mypackage_arm.deb .
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$ cd $HOME/myRootImage
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  $ dpkg -x $HOME/arm_debs/mypackage_arm.deb .
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Now we create a new tarball from the working directory of the image.
Now we create a new tarball from the working directory of the image.
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  $ cd $HOME/myRootImage
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  cd $HOME/myRootImage
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  $ tar cvzf $HOME/myNewRootImage.tar.gz .
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  tar cvzf $HOME/myNewRootImage.tar.gz .
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=Installing into Nokia 770=
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When the new tarball is created, refer to HOWTO: Using flasher and the reference root filesystem for creating JFFS2 image from the myNewRootImage.tar.gz.
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Use flasher to install the image to Nokia 770.
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$ ./flasher --flash-only rootfs -F image.bin -f
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$ ./flasher --rootfs rootfs.jffs2 --flash-only rootfs --flash
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$ ./flasher --enable-rd-mode --reboot
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The flash-only parameter is used just to make sure ;-)
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 +
== Installing on the tablet ==
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When the new tarball is created,  Using flasher and the reference root filesystem for creating JFFS2 image from the myNewRootImage.tar.gz.
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=Final remarks=
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Use flasher to install the image on the tablet.
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Tonight, I had to re-flash the first time, as I screwed up a script in /etc/init.d/. For the future, I will try to make a full backup of my productive rootfs, to avoid starting all over again
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 +
./flasher-3.0 -r rootfs.jffs2 --f -R
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--------------------------------------------------------------------------------
 
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=Shell script to mount/unmount JFFS2 using Block device Emulating MTD=
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== Shell script to mount/unmount JFFS2 using block device emulating MTD ==
Create a shell script (mount_jffs2.sh) from the following:
Create a shell script (mount_jffs2.sh) from the following:
<pre>
<pre>
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Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.
Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.
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Usage: $ ./mount_jffs2.sh rootfs.jffs2
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Usage:
 +
 
 +
./mount_jffs2.sh rootfs.jffs2
You can also use this script to unmount and unload the non-utilized kernel modules and loopback reference:
You can also use this script to unmount and unload the non-utilized kernel modules and loopback reference:
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$ ./mount_jffs2.sh rootfs.jffs2 unmount
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./mount_jffs2.sh rootfs.jffs2 unmount
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--------------------------------------------------------------------------------
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== Shell script to mount/unmount JFFS2 using kernel memory emulating MTD ==
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+
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=Shell script to mount/unmount JFFS2 using Kernel Memory Emulating MTD=
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Create a shell script (mount_jffs2.sh) from the following:
Create a shell script (mount_jffs2.sh) from the following:
<pre>
<pre>
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Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.
Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.
-
Usage: $ ./mount_jffs2.sh rootfs.jffs2
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Usage:
 +
./mount_jffs2.sh rootfs.jffs2
You can also use this script to unmount and unload the non-utilized kernel modules:
You can also use this script to unmount and unload the non-utilized kernel modules:
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$ ./mount_jffs2.sh rootfs.jffs2 unmount
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./mount_jffs2.sh rootfs.jffs2 unmount
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--------------------------------------------------------------------------------
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=Maybe one could write a script removing unwanted stuff from that image (sample video, song), changing sudoers, gainroot script, adding sshd, ...=
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Revision as of 12:32, 8 July 2008

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This is an article from the old midgard wiki that hasn't yet been fully updated for this wiki, please update it.
Please see the talk page for discussion.


This article describes two methods for extending and modifying an existing tablet JFFS2 root image.

Contents

Background

The root filesystem (rootfs) of the tablets is stored in a Journal Flash File System version 2 (JFFS2) format. It resides on one of the partitions on the flash chip in the device. Additionally, a pristine version of the rootfs can be obtained from the Nokia official firmware site.

There are two ways to mount the JFFS2 image:

  1. Have a block device emulate a Memory Technology Device (MTD) via blkmtd (v2.4.x Linux kernels) or block2mtd (v2.6.x Linux kernels)
  2. Have kernel memory emulate a MTD via mtdram

Getting the JFFS2 image

First of all, we need to get the rootfs.jffs2 from the official Nokia FIASCO image. After downloading the FIASCO image, run this on it to unpack it (this will give you all of the individual parts of the image):

sudo ./flasher-3.0 --unpack  -F <FIASCO image>

Mounting the JFFS2 image

These commands will be executed with root privileges on the host machine and not on the device itself.

Block device emulating an MTD device

You must have the following kernel modules compiled and installed:

  • CONFIG_MTD (mtdcore)
  • CONFIG_MTD_PARITIONS (mtdpart)
  • CONFIG_MTD_MTDRAM (mtdram)
  • CONFIG_MTD_BLOCK2MTD (block2mtd)
  • CONFIG_BLK_DEV_LOOP (loop)

I suggest you do not make these modules statically linked into the kernel. It is more practical to be able to unload these modules when not needed or when you want to start over from scratch.

You will use the loopback device (/dev/loop[0-15]) to simulate a block device whose contents are from the JFFS2 image. To mount the JFFS2 image, you perform the following steps:

mknod /tmp/mtdblock0 b 31 0
modprobe loop
losetup /dev/loop0 rootfs.jffs2
modprobe mtdblock
modprobe block2mtd
echo "/dev/loop0" > /sys/module/block2mtd/parameters/block2mtd
modprobe jffs2
mount -t jffs2 /tmp/mtdblock0 /media/jffs2

To unmount and cleanup:

umount /media/jffs2
modprobe -r block2mtd
modprobe -r mtdblock
losetup -d /dev/loop0

Kernel memory emulating an MTD device

To mount the JFFS2 image, you perform the following steps:

mknod /tmp/mtdblock0 b 31 0
modprobe mtdblock
modprobe mtdram total_size=65536 erase_size=256
modprobe jffs2
dd if=/pathtoimage/rootfs.jffs2 of=/tmp/mtdblock0
mkdir /media/jffs2
mount -t jffs2 /tmp/mtdblock0 /media/jffs2

To unmount and cleanup:

umount /media/jffs2
modprobe -r jffs2
modprobe -r mtdram
modprobe -r mtdblock

Archiving and extracting the rootfs image

The image is now accessible under /media/jffs2. Copy the whole image to another directory. This new directory will be used for modifying the image. Extending the currently mounted JFFS2 image is not suggested. Using cp for copying the image to a working directory won't work due to special files in /media/jffs2/dev, which is why we use tar.

cd /media/jffs2
tar cvzf /my_path/myRootImage.tar.gz .
cd $HOME
mkdir myRootImage
cd myRootImage
tar xvpzf /my_path/myRootImage.tar.gz

Modifying the copy of the image

Now the image is successfully archived and copied. The working directory $HOME/myRootImage can now be used for adding, changing or modifying packages.

cd $HOME/myRootImage
dpkg -x $HOME/arm_debs/mypackage_arm.deb .

Now we create a new tarball from the working directory of the image.

cd $HOME/myRootImage
tar cvzf $HOME/myNewRootImage.tar.gz .

Installing on the tablet

When the new tarball is created, Using flasher and the reference root filesystem for creating JFFS2 image from the myNewRootImage.tar.gz.

Use flasher to install the image on the tablet.

./flasher-3.0 -r rootfs.jffs2 --f -R


Shell script to mount/unmount JFFS2 using block device emulating MTD

Create a shell script (mount_jffs2.sh) from the following:

 #!/bin/sh
 JFFSIMG=$1 # jffs image
 LOOP="/dev/loop1" # loop device
 MP="/media/jffs2" # mount point
 MTDBLOCK="/tmp/mtdblock0" # MTD device file
 KVER="2.6"
 BLKMTD="block2mtd"
 UMNT=""

 echo "$0" | grep unmount_ >/dev/null 2>&1
 [ $? -eq 0 ] && UMNT=1
 if [ $# -gt 1 -a x"$2"x = x"unmount"x ]; then
   UMNT=1
 fi

 uname -r | egrep '^2\.6' >/dev/null 2>&1
 if [ $? -ne 0 ]; then
   KVER="2.4"
   BLKMTD=blkmtd
 fi 

 if [ x"${UMNT}"x = x""x ]; then
   if [ ! -b ${MTDBLOCK} ] ; then
     mknod ${MTDBLOCK} b 31 0 || exit 1
   fi
   lsmod | grep loop >/dev/null 2>&1
   if [ $? -ne 0 [; then
     modprobe loop
     [ $? -ne 0 ] && echo "loopback loading failed" && exit 1
     sleep 1
   fi
   losetup ${LOOP} ${JFFSIMG} || exit 1
   sleep 1
   modprobe mtdblock
   if [ x"${KVER}"x = x"2.4"x [; then
     modprobe ${BLKMTD} device=${LOOP} || exit 1
   else
     modprobe ${BLKMTD} || exit 1
     echo "${LOOP}" > /sys/module/block2mtd/parameters/block2mtd
   fi
   sleep 1
   modprobe jffs2
   [ ! -d ${MP} ] && mkdir -p ${MP}
   mount -t jffs2 ${MTDBLOCK} ${MP} || exit 1
 else
   umount ${MP}
   if [ $? -ne 0 ]; then
     echo "Cannot unmount JFFS2 at $MP" && exit 1
   fi
   modprobe -r jffs2
   modprobe -r ${BLKMTD}
   modprobe -r mtdblock
   sleep 1
   losetup -d ${LOOP}
 fi 

Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.

Usage:

./mount_jffs2.sh rootfs.jffs2

You can also use this script to unmount and unload the non-utilized kernel modules and loopback reference:

./mount_jffs2.sh rootfs.jffs2 unmount


Shell script to mount/unmount JFFS2 using kernel memory emulating MTD

Create a shell script (mount_jffs2.sh) from the following:

 #!/bin/sh
 JFFSIMG=$1 # jffs image
 MP="/media/jffs2" # mount point
 MTDBLOCK="/tmp/mtdblock0" # MTD device file
 UMNT=""

 echo "$0" | grep unmount_ >/dev/null 2>&1
 [ $? -eq 0 ] && UMNT=1
 if [ $# -gt 1 -a x"$2"x = x"unmount"x ]; then
   UMNT=1
 fi

 if [ x"${UMNT}"x = x""x ]; then
   if [ ! -b ${MTDBLOCK} ] ; then
     mknod ${MTDBLOCK} b 31 0 || exit 1
   fi
   modprobe mtdblock
   modprobe mtdram total_size=65536 erase_size=256
   modprobe jffs2
   dd if=${JFFSIMG} of=${MTDBLOCK}
   [ ! -d ${MP} ] && mkdir -p ${MP}
   mount -t jffs2 ${MTDBLOCK} ${MP}
 else
   umount ${MP}
   if [ $? -ne 0 ]; then
     echo "Cannot unmount JFFS2 at $MP" && exit 1
   fi
   modprobe -r jffs2
   modprobe -r mtdram
   modprobe -r mtdblock
 fi 

Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.

Usage:

./mount_jffs2.sh rootfs.jffs2

You can also use this script to unmount and unload the non-utilized kernel modules:

./mount_jffs2.sh rootfs.jffs2 unmount