works for me with barrier breaker. added some readme, too.

README.md

@@ -1,4 +1,54 @@
-* This is more of a template than something standalone
+# What
 
-I've extracted this from another project, but I think it's useful
-enough for making it public.
+It's a script to build a customized OpenWRT firmware that will
+automatically set up
+[extroot](http://wiki.openwrt.org/doc/howto/extroot) on any (!)
+storage device plugged into the USB port (`/dev/sda`).
+
+# Why
+
+So that e.g. customers can buy a router on their own, flash our
+firmware, plug in a pendrive, and manage their SIP (telephony) node
+from our webapp.
+
+# Status
+
+This is more of a template than something standalone. You most
+probably want to customize this script here and there; search for
+`CUSTOMIZE` for places of interest.
+
+I've extracted this from a project where OpenWRT nodes auto-provision
+themselves in 3 stages, but I thought it's useful enough for making it
+public (stage 1: extroot setup; stage 2: install packages; stage 3: a
+Python script for app-level sync).
+
+At the time of writing it only supports a few `ar71xx` routers but
+it's easy to extend it.
+
+## Tested with
+
+[OpenWRT Barrier Breaker 14.07](http://downloads.openwrt.org/barrier_breaker/14.07/)
+on a TP-Link WDR4300.
+
+# Building
+
+e.g. `./build.sh TLWDR4300`
+
+Results will be under `build/OpenWrt-ImageBuilder-ar71xx_generic-for-linux-x86_64`.
+
+# Usage
+
+After flashing the firmware the router will have the standard
+`192.168.1.1` IP address, and SSH will listen there using the keys
+specified in `image-extras/etc/dropbear/authorized_keys`.
+
+Once connected, you can read the log with `logread -f`.
+
+The autoprovision script will wait for any `/dev/sda` to show up, then
+erase it and set up a `swap`, an `extroot`, and a `data` filesystem,
+and then reboots.
+
+In stage 2 it will need an internet connection, so you should connect
+to its [LuCI interface](http://192.168.1.1) to set up an Internet
+upstream, and then it will automatically continue installing packages,
+finishing the whole process, and then do a final reboot.