How do you generate the SWU file?

[jelalanne]

Hello,
I would like to know how do you all generate your SWU files, and what do they have inside?

[jw-msft]

@jelalanne We use Yocto to build the .swu such as the adu-update-image-raspberrypi3-1.0.2-2.swu that is in https://github.com/Azure/iot-hub-device-update/releases/download/1.0.2/Tutorial_RaspberryPi.zip

You can do similarly by following the README.md here:
https://github.com/Azure/iot-hub-device-update-yocto

The .swu format in SWUpdate is a CPIO archive that typically has the following files (in the order specified):

• sw-description metadata for swupdate
• sw-description.sig signature file ensure integrity of the file hashes and other metadata in the sw-description file
• one or more payload files

There is a diagram and more info on SWUpdate's doc page here:
https://sbabic.github.io/swupdate/swupdate.html#single-image-delivery

On an x64 desktop linux box, you can examine the contents of the 1.0.2 release .swu files built using Yocto recipe for Raspberry Pi 3 board by doing the following:

wget https://github.com/Azure/iot-hub-device-update/releases/download/1.0.2/Tutorial_RaspberryPi.zip
unzip Tutorial_RaspberryPi.zip
cd Tutorial_RaspberryPi

# List contents of .swu CPIO archive:
cpio -i --list < adu-update-image-raspberrypi3-1.0.2-2.swu

# Unpack the contents of .swu CPIO archive
cpio -i < adu-update-image-raspberrypi3-1.0.2-2.swu

# contents of sw-description and .sig
cat sw-description
base64 sw-description.sig

# uncompress ext4 raw disk image, mount it read-only on loopback device, and explore
gunzip adu-base-image-raspberrypi3.ext4.gz
sudo mkdir /mnt/rpi3
sudo mount -o loop,ro adu-base-image-raspberrypi3.ext4 /mnt/rpi3
cd /mnt/rpi3
ls -latr

[jelalanne]

Thanks for your answer! I forgot to mention that I was looking for another solution than Yocto, because we use CustomPiOS to generate our full image file, and I was wondering if people use cpio or maybe swugenerator, and what was the content of their file for a swupdate:2 update type.

For anyone who has the same question, I generate the swu file with a ext4 partition file which is just the extraction of the primary root fs of the full image, indicated as a raw file in sw-description. I'm not sure that my solution is reliable so I prefer to ask you how i should do it for production-ready before saying something wrong.