UKI based container: /var issues

[rlees85]

Still working through trying to learn bootc and how to create containers based on composefs (sealed) and UKI (no point starting with the older stuff I guess).

Very nearly have it working, just a few remaining issues with /var:

• By default I noticed that /sysroot, /etc and /var get mounted as read-only. This obviously doesn't boot. I noticed here: https://github.com/travier/fedora-atomic-desktops-sealed/blob/main/scripts/prepare-rootfs.sh that when the file system is btrfs you manually add in a rw kernel argument. I assumed this wasn't relevant as I'm using ext4 but adding in rw manually fixes this. Expected... or?
• When shutting down, systemd complains that var.mount (/var) fails to unmount. Apart from this, it shuts down cleanly. Is this expected or should I be doing something else to my image to make sure /var gets cleanly unmounted? This is not a problem on vanilla Silverblue