Latest revision as of 11:20, 17 March 2011

NFS-root over usb networking

This page describes howto make N900 boot a MeeGo root filesystem from your host (PC) using USB networking. If you choose to load kernel and initrd, then nothing needs to be changed in your N900. Two different approaches are described:

• using initrd (no compilation of any sw components required)
• using customized kernel (requires kernel recompilation)

Initrd is the preferred method.

Requirements

• USB networking
• a MeeGo rootfs image

Obtaining the rootfs image

First, you have to get/make a MeeGo rootfs image. You can download a pre-built raw image (ARM/N900#Releases) or create your own (ARM/Creating ARM image using MeeGo Image Creator).

Preparing the root filesystem

Mount the unpacked raw image to temporary directory and copy the contents to suitable location on your host system. Here we use /home/nfs/rootfs.

NOTICE: the offset of the mount command depends on image. offset=512*start_sector. Check the start sector of your image by running command: (In our prebuilt image the start sector was 1)

file yourimage.raw

bunzip2 meego-n900-*.raw.bz2
mkdir temp
mount -o loop,offset=512 meego-*.raw temp
mkdir -p /home/nfs/rootfs
cp -ax temp/* /home/nfs/rootfs/

nokia-usb-networking script conflicts with nfsroot thus it must be removed.

rm /home/nfs/rootfs/etc/rc.d/rc3.d/S50nokia-usb-networking

Installing NFS server

Next, make sure you have NFS server installed on your host and export the rootfs.

apt-get install nfs-kernel-server  ### Ubuntu
yum install nfs-utils              ### Fedora
echo '/home/nfs      192.168.2.15(rw,no_root_squash,no_subtree_check)' >> /etc/exports
exportfs -v -a

Method 1: NFS-Root with initrd

This method involves using busybox from MeeGo and does not require kernel recompilation. You can more easily keep in sync with the MeeGo kernel.

Preparing initrd directory

First, you have to create a directory for preparing initrd. We'll create that under the rootfs directory (but you could create it anywhere you like, of course).

 mkdir /home/nfs/rootfs/initrd

You need some initial directories:

cd /home/nfs/rootfs/initrd
mkdir bin
mkdir sbin
mkdir proc
mkdir sys
mkdir dev
mkdir mnt
mkdir -p lib/modules

Some device nodes are needed by the kernel (note, these must be run as root to preserve device node properties):

cp -a /dev/console dev/
cp -a /dev/null dev/
cp -a /dev/ram0 dev
cp -a /dev/tty dev/
cp -a /dev/tty0 dev/
cp -a /dev/zero dev/

Copy kernel modules from your rootfs to the initrd (be sure to use correct kernel version):

cp -r /home/nfs/rootfs/lib/modules/2.6.* lib/modules/

Installing Busybox

As the next step, you need Busybox. If you have busybox installed in you rootfs, you can simply:

cp /home/nfs/rootfs/sbin/busybox bin/

If you don't, you can get the binary e.g. by fetching the busybox rpm package and extracting the binary from there

mkdir tmp
cd tmp
wget http://repo.meego.com/MeeGo/releases/1.0/core/repos/armv7l/packages/armv7l/busybox-1.16.0-3.1.armv7l.rpm
rpm2cpio busybox-1.16.*.armv5tel.rpm | cpio -id
cp sbin/busybox /home/nfs/rootfs/initrd/bin/
cd ..
rm -rf tmp

Now, you have the busybox binary installed. Currently, MeeGo does not have a statically compiled version of Busybox. Thus, you need some libraries as well:

cp /home/nfs/rootfs/lib/ld-linux.so.3 lib/
cp /home/nfs/rootfs/lib/libc.so.6 lib/
cp /home/nfs/rootfs/lib/libm.so.6 lib/

Last, you need to set up some links to the busybox binary:

cd bin
ln -s busybox sh
ln -s busybox mount
ln -s busybox modprobe
ln -s busybox sleep
ln -s busybox ifconfig
ln -s busybox echo
ln -s busybox umount
ln -s busybox pivot_root
ln -s busybox exec
ln -s busybox cd
ln -s busybox ls
ln -s busybox chroot
cd ..

Now, you're done with Busybox.

Making initrd to boot automatically

Next, make a script for doing the actual NFS-rooting and :

vim autonfsroot.sh
# edit the script, an example is found below
chmod a+x autonfsroot.sh
rm sbin/init
ln -s ../autonfsroot.sh sbin/init

Here's a simple example of autonfsroot.sh

#!/bin/sh
echo "Doing mounts..."
mount -t proc proc /proc
mount -t sysfs sysfs /sys

echo "Loading modules..."
modprobe sunrpc
modprobe auth_rpcgss
modprobe rpcsec_gss_krb5
modprobe nfs
modprobe phonet
modprobe g_nokia

sleep 2

echo "Configuring network interface..."
ifconfig usb0 192.168.2.15

echo "Mounting NFS..."
mount -t nfs -o nolock 192.168.2.14:/home/nfs/rootfs /mnt

echo "Unmounting proc and sys..."
umount /proc
umount /sys

echo "Switching to nfsroot..."
# switch_root does not seem to be working with cramfs
#exec switch_root /mnt /sbin/init
cd /mnt
pivot_root . mnt
exec chroot . /sbin/init

Of course, you could do more elaborate scripting, e.g. add automatic kernel command line parsing/analysis, but that's not covered here.

Making initrd image and booting

N900 requires cramfs initrd images. This is a bootloader restriction. Go back to the directory containing the initrd dir and then:

cd ..
mkfs.cramfs -b 4096 -n meego_initrd ./initrd/ initrd.img

Now you are ready to load your kernel + initrd with flasher and boot to nfs-root. Interface usb0 should be assigned an IP right after the loading.

NOTICE: Here we do not flash the kernel or initrd to the device, but only load them to the device memory during the boot. Original images are restored when the device is restarted.

• Turn off your device by removing battery.
• Start flasher by:

sudo flasher -k /home/nfs/rootfs/boot/vmlinuz-VERSION_HERE -n initrd.img -l -b"root=/dev/ram0" ; \
sleep 5 ; sudo ifconfig usb0 192.168.2.14

• Connect N900 to your PC with the USB cable (directly ! some HUBS may cause strange problems)
• Start the device by inserting the battery.
• Now you should see MeeGo booting. It will take over a minute for xterm to appear.

Method 2: NFS-Root with custom kernel

As a pre-requisite, you have to have environment for cross-building ARM binaries.

Then, you have to recompile kernel for N900. You must enable (built inside kernel, thus select '*', not 'M'):

* USB Gadget support (Device drivers -> USB Support -> USB Gadget support)
  * USB Gadget drivers (Device drivers -> USB Support -> USB Gadget support -> USB Gadget drivers)
    * Ethernet gadget
      * RNDIS Support (Device drivers -> USB support -> USB Gadget support -> RNDIS support)
      * Ethernet Emulation Model (EEM) support (Device drivers -> USB support -> USB Gadget support -> EEM support)
* NFS support (File systems -> Network File systems -> NFS client support)
  * NFS-Root support (File systems -> Network File systems -> NFS client support -> Root file system on NFS)
* IP kernel autoconf (Networking support -> Networking options -> IP: kernel level autoconfiguration)
  * all sub-options

Compile and install modules

make
make modules_install INSTALL_MOD_PATH=/home/nfs/rootfs

After compilation is finished you can boot the new kernel with (assuming 192.168.2.14 is your host) NOTICE: Here we do not flash the kernel or initrd to the device, but only load them to the device memory during the boot. Original images are restored when the device is restarted.

• Turn off your device by removing battery.
• Start flasher by:

flasher -k arch/arm/boot/zImage -l -b"init=/sbin/preinit ip=192.168.2.15::192.168.2.14 root=/dev/nfs \
nfsroot=192.168.2.14:/home/nfs/rootfs rootdelay=2 rw console=ttyMTD console=tty0"

• Connect N900 to your PC with the USB cable (connect directly, some HUBS may cause problems)
• Start the device by inserting the battery.
• Now you should see MeeGo booting.

Advanced option

You can also hard code the kernel command line options as default when recompiling the kernel (Boot options -> default kernel command string). Further, you can also flash the new kernel to the device by:

NOTICE: If you choose to flash the kernel, original image (e.g. Maemo 5) will not start and you need to flash the original kernel back before normal use.

sudo flasher-3.5 -f -k <kernel_image>

But still, you have to override the Nolo command line options on every startup with flasher:

flasher -b]