Update strategy for the not just the app but the whole system.

[martonborzak]

Let's try to start thinking about it how to do it.

For inspiration:
https://mkrak.org/2018/01/10/updating-embedded-linux-devices-part1/

[zehnm]

Summary of our discussion, feedback from Discord and initial experiments:

• Using SWUpdate as system update framework
  • Optional web server allows uploading system image and triggering update
• A / B system partition setup for failsafe system updates
• U-Boot for choosing the valid system partition
  • Boot counter & setting U-Boot env variable in Linux after successful boot
  • After n failed boots: switch back to the old partition

Open issues:

• Partition layout details: Add partitions for software update #16
  • One data partition or A / B data partitions.
• Read only system partition: Make the Remote SD card read-only #49
  • The initial system update feature will most likely have regular read-write system partitions.

Further resources:

• https://www.embedded.com/ota-updates-for-embedded-linux-part-1-fundamentals-and-implementation/
• https://afterhourscoding.wordpress.com/2020/07/26/integrating-swupdate-with-u-boot/
• https://mkrak.org/wp-content/uploads/2018/04/FOSS-NORTH_2018_Software_Updates.pdf
• https://www.slideshare.net/MenderOTA/the-ultimate-guide-to-software-updates-on-embedded-linux-devices
• https://bootlin.com/blog/building-a-linux-system-for-the-stm32mp1-remote-firmware-updates/
• https://www.embedded-software-engineering.de/automatisches-firmware-update-fuer-embedded-linux-a-833310/
• Newer Android versions also use A / B updates: https://source.android.com/devices/tech/ota/ab
  There's even support in U-Boot, but I don't think we could easily (ab)use that for a regular Linux system.