nerves_uboot_env_ubi

A Nerves.Runtime.KVBackend for boards whose U-Boot environment lives in UBI volumes on raw NAND/NOR flash.

Why?

Writing to a UBI volume character device (/dev/ubi0_N) requires the UBI_IOCVOLUP ioctl to enter atomic-update mode. Plain pwrite/2 — used by Erlang's :file module and the default Nerves.Runtime.KVBackend.UBootEnv — returns EPERM. So the stock Nerves backend can't write the U-Boot env on UBI-backed systems, and Nerves.Runtime.validate_firmware/0 fails with {:error, :eperm}, which in turn breaks Nerves.Runtime.StartupGuard.

This backend reads through the Erlang UBootEnv library (pread/3 works fine on /dev/ubi*) and writes by shelling out to the C fw_setenv tool from u-boot-tools, which issues the UBI_IOCVOLUP ioctl transparently.

Requirements

The Nerves system / target must provide:

/etc/fw_env.config pointing at the UBI volumes holding the env. Per-volume paths only (e.g. /dev/ubi0_0), not the /dev/ubi0:<volname> colon syntax — Erlang's UBootEnv opens the path with :file.open/2 and can't parse the colon-name shorthand that the C tools accept.
fw_setenv on the device (defaults to /usr/sbin/fw_setenv). Buildroot's BR2_PACKAGE_UBOOT_TOOLS_FWPRINTENV=y ships this.

Installation

def deps do
  [
    {:nerves_uboot_env_ubi, "~> 0.1"}
  ]
end

In config/target.exs:

config :nerves_runtime,
  kv_backend: {Nerves.Runtime.KVBackend.UBootEnvUBI, []}

If your fw_setenv lives somewhere other than /usr/sbin/fw_setenv:

config :nerves_runtime,
  kv_backend: {Nerves.Runtime.KVBackend.UBootEnvUBI,
               [fw_setenv: "/sbin/fw_setenv"]}

Status

Used in production on the OpenWRT One Nerves system. Should work on any Linux board where the U-Boot env is in UBI volumes — OpenWrt-derived MediaTek Filogic boards, Banana Pi BPi-R3, etc.

License

Apache-2.0. See LICENSE.