It’s written specifically to host the Linux kernel, and doesn’t use a bios or a boot loader. If you backported that into another hypervisor, it would probably have to be something like “are we loading a compatible Linux? If so switch to Firecracker mode”. But of course you can do that yourself, with a small shell script that either starts the traditional VM or Firecracker.
> The recommended way to trigger a guest-initiated shut down is by generating a triple-fault, which will cause the VM to initiate a reboot
Doesn’t that mean it can’t distinguish an intentional triple fault to trigger reboot from an accidental triple fault caused by a guest kernel bug which corrupts the IDT? I think it would be better if there was some kind of call the guest could make to the hypervisor to reboot-one is less likely to invoke that service by accident than to triple fault by accident.
I'm used to QEMU VMs being slow and annoying to work with due to them being full VMs, so I was quite surprised to see that this is really just as fast as Firecracker!
I'm assuming that Firecracker is somewhat constrained in some way.