Handling nand flash to save/recover data using ArchLinuxArm

When booting from SDCard under linux, it is possible to access the NAND partitions.
I use ArchLinux ARM, following this tutorial: Mele A100, the only bootable image that gets correctly the NAND partitions (as under Android ICS). I changed the MAC entry in script.bin in order to have a well-known MAC address for ssh.

Under Android ICS, partitions are defined like this:

-dev-  -name-        -start-       -size-       -mountpoint-


nanda  bootloader  : 1000000       01000000      u-boot
nandb  env         : 2000000       01000000      N/A (u-boot environment)
nandc  boot        : 3000000       02000000      initrd in RAM as / + kernel
nandd  system      : 5000000       20000000      /system
nande  data        : 25000000      60000000      /data
nandf  misc        : 85000000      01000000      "boot-recovery" or 0xff*
nandg  recovery    : 86000000      02000000      N/A (recovery image)
nandh  cache       : 88000000      08000000      /cache
nandi  private     : 90000000      01000000      /mnt/private
nandj  sysrecovery : 91000000      20000000      /mnt/sysrecovery
nandk  UDISK       : b1000000      3b000000      /sdcard

Under Linux, partitions are detected correctly (the following line shows something comparable to the above output):

echo "-dev-  -size-";cat /proc/partitions|while read x y size dev; do echo "$dev  `printf %08x $(( $size * 1024 ))`";done
[...]
-dev-  -size-
[...]
nanda  01000000
nandb  01000000
nandc  02000000
nandd  20000000
nande  60000000
nandf  01000000
nandg  02000000
nandh  08000000
nandi  01000000
nandj  20000000
nandk  3c800000
[...]

As a consequence, you can read/edit/save data from NAND using a linux distribution.

Important note: don't write on Android ICS mounted partitions, you can corrupt data!
Use cases:

1/ list installed application in /data:

mount -o noatime,nosuid,nodev,barrier=0,journal_checksum,noauto_da_alloc /dev/nande /mnt #this is how Android mounts ext4 partitions, look at init.sun4i.rc for special nand mount options.

ls -l /mnt/app/

-rw-r--r-- 1 1000 1000  4707663 Nov  5  2012 com.adobe.flashplayer-1.apk       

[...]

2/ backup a NAND partition locally:

dd if=/dev/nande bs=4096 |bzip2 -c >/root/nande.bz2

3/ backup a NAND partition via ssh (assuming my ssh server is at @192.168.1.124):

dd if=/dev/nande bs=4096 |bzip2 -c | ssh user@192.168.1.124 dd of=/home/user/nande.bz2

4/ restore a NAND partition locally:

bzip2 -cd /root/nande.bz2 | dd of=/dev/nande bs=4096

sync

5/ restore a NAN partition via ssh:

ssh user@192.168.1.124 bzip2 -cd /home/user/nande.bz2 | dd of=/dev/nande bs=4096

6/ make a tar.bz2 archive of a partition contents (for huge partitions, instead of saving raw data):

mount -o noatime,nosuid,nodev,barrier=0,journal_checksum,noauto_da_alloc /dev/nande /mnt
cd /mnt
tar jcf - .|ssh user@192.168.1.124 dd of=/home/user/nande.tar.bz2
cd
umount /mnt

Using these commands, you can save/restore completely some essential partitions before a crash or a new firmware flashing procedure (/data essentially, /sdcard contains user data - movies, ... - that you should save in another place by other means).