cloud-hypervisor watchdog requires kernel patch

[jpds]

Leaving a note that the cloud-hypervisor watchdog (which microvm.nix enables by default) requires this kernel patch to actually be enabled inside the guest:

• drivers/watchdog: Add paravirtualized virtio-watchdog cloud-hypervisor/linux#3

[astro]

How important is that to cloud-hypervisor users? Requiring users to build a custom kernel should be opt-in ever since we can boot the binary-cached NixOS kernel with initramfs. Is that driver going to be sent to upstream Linux?

Once we have an opt-in flag for custom kernels, it would be cool to make the initramfs optional in cases where virtio_blk is statically built-in.