[met67]

For the sake of completeness I am posting the code that I added to upgrade-wifi.sh and wich is responsible for the backup:

#
# Dump internal firmware on uSD
#
if [ -e /dev/mmcblk1p1 ]; then
  # mount uSD (umount first just in case udevd has already mounted it in readonly)
  umount /mnt/sd
	dosfsck -a -w /dev/mmcblk1p1
  mount -t vfat -o iocharset=utf8 /dev/mmcblk1p1 /mnt/sd

  if [ -e /mnt/sd/KoboDump ]; then
    # mount / as readonly and unmount internal FAT
    mount -o remount,noatime,nodiratime,ro /dev/mmcblk0p1 /
    umount /mnt/onboard

    # test uSD: if mount failed, /mnt/sd/.123sdcheck123 can't be created since / is readonly
    touch /mnt/sd/KoboDump/.123sdcheck123
    if [ -e /mnt/sd/KoboDump/.123sdcheck123 ]; then
      rm -rf /mnt/sd/KoboDump/.123sdcheck123
      # dump...
      dd if=/dev/mmcblk0 of=/mnt/sd/KoboDump/dump.img bs=512
      # rename KoboDump to avoid (improbable) loops
      mv /mnt/sd/KoboDump /mnt/sd/KoboDumpDone
    fi
    # restore mounted devices as expected
    mount -o remount,noatime,nodiratime,rw /dev/mmcblk0p1 /
    mount -t vfat -o iocharset=utf8 /dev/mmcblk0p3 /mnt/onboard
  fi
  umount /mnt/sd
fi