Ship initoverlayfs with nmbl

[ericcurtin]

Hi Guys,

initoverlayfs was something I was working on for embedded use cases:

https://github.com/containers/initoverlayfs

it replaces initramfs with an erofs+overlayfs which leads to more scalable, faster initial filesystems, as in initoverlayfs we only read, verity bytes, etc. as we use them. Rather than cpio blob initramfses which are space sensitive due to the multiple copied of the data performed to populate that filesystem.

It was intended for our Automotive offerings, but recently we instead starting doing per-board OS builds, making our initramfses custom per-board, which makes them really tiny < 10 M making initoverlayfs only a handful of milliseconds faster when your initramfs is super small.

But in a generic operating system with a larger initramfs like Fedora or RHEL initoverlayfs makes even more sense, and it allows you to use larger binaries, etc. early boot.

To get the best performance out of initoverlayfs you need to build persistent storage drivers directly into the kernel, kinda like grub/sd-boot does.

With nmbl acting like a bootloader in Linux, maybe there's an opportunity to build persistent storage drivers directly in like a bootloader and ship initoverlayfs with nmbl

Interested in your feedback:

https://github.com/containers/initoverlayfs