create_disk: Support rootfs-size

[cgwalters]

For RHCOS with encryption, we encrypt in early boot, and it's beneficial
if the root filesystem size is small initially - distinct from the
"default disk" size that applies in clouds (and libvirt).

This helps RHCOS maintain its default 16G size for libvirt without
requiring the installer and other tools to start resizing it.

[cgwalters]

Alternatively...we could use the same space estimation we do for metal across the board by default.

[cgwalters]

One benefit/downside of this is that we'd start always having coreos-growpart.service expand on boot, even in qemu.

[cgwalters]

Or maybe we should do the "size estimation" even for qemu.

[jlebon]

Just making sure I follow here. On bare metal, we growpart to the size of the actual disk. On clouds, we growpart to the size of the allocated disk. So it's only on qemu/libvirt that the number we put in size is used as is, correct? I'm confused from openshift/installer#2652 (comment) why the installer isn't doing the resize itself since it's the equivalent of choosing the storage size on clouds (which it already does today).

Anyway, as to the rootfs itself, I like the idea of being consistent everywhere (using size estimation). (It also makes it easier to add more partitions after the rootfs via Ignition for testing.)

[cgwalters]

Anyway, as to the rootfs itself, I like the idea of being consistent everywhere (using size estimation). (It also makes it easier to add more partitions after the rootfs via Ignition for testing.)

Yeah I'm working on this.

(It also makes it easier to add more partitions after the rootfs via Ignition for testing.)

A bit, but you can also just cosa run --size 26 for that too.

[cgwalters]

Don't need this anymore.