Rootfs on NFS

With the OpenEzx kernel, here is how to mount an NFS root, over the USBNet interface on a linux host box.

Assuming you have the nfs support and usbnet compiled and working on your kernel.

With some kernels, you may need to unplug/plug the USB cable for the phone to be recognized, and the network to be reachable (this will force the USB's re-enumeration).

1. Configure the PC's USB Network.

So, at first you need to load/install the modules "usbnet", perhaps also "cdc_subset".

Assign the IP address to suit your kernel's config/CMDLINE

Example /etc/network/interfaces (for debian based distros)

#Addition for the EZX network interface
auto usb0
iface usb0 inet static
        address 192.168.0.200
        netmask 255.255.255.0
        broadcast 192.168.0.255

It's often recommended to use these lines too:

mapping hotplug
script grep
map usb0

Note that I still need to do an "ifup usb0", when I plug my phone on the ubuntu machine...

There is a bug on ubuntu, causing this solution to only work once at each boot. See [1]

I found a workaround on this page: [2]

(You simply need to move DRIVERS=="*?" in the file /etc/udev/rules.d/85-ifupdown.rules from GOTO to the big ACTION=="add" line.)

2. Install NFS.

On ubuntu :

sudo apt-get install nfsboot (depends on bind9, atftpd, openbsd-inetd)
sudo apt-get install nfs-common nfs-kernel-server

Edit /etc/export to suit the path the kernel will be waiting for.

Example /etc/export (You can add some mounting options here too):

/PATH/TO/YOUR/NFSROOT/EXPORT   192.168.0.202(rw,no_root_squash,async)

3. Example kernel command line for nfs root.

Please adjust for your personal needs.

CMDLINE_ROOT = "root=/dev/nfs nfsroot=192.168.0.200:/PATH/TO/YOUR/NFSROOT/EXPORT/ rootdelay=5"

For deeper explanation, you can refer to Documentation/filesystems/nfsroot.txt and the nfs manual page.