Re: virtio_mmio.device parameter unknown as kernel config option is disabled
On Thu, Mar 05, 2020 at 10:31:37PM +0100, João Mikos wrote:
> I am experimenting with running a Debian Buster microVM under the
> Firecracker hypervisor, using a stock Debian kernel (converted to
> vmlinux format) and an initrd.img file. When booting the microVM with
> this setup, I receive the following error message inside the microVM,
> which halts booting:
Hi João. I have extensive experience with Firecracker, with both Debian
and other distros as the guest OS. In general, the expectation with
Firecracker is that it will not work with distro kernels out-of-the-box,
but that it requires a custom kernel specifically configured for MicroVM
deployments. Keep in mind that Firecracker originally didn't even
provide initramfs support, meaning that all device and filesystem
drivers needed to be statically linked into the kernel. Although
Firecracker has since added initramfs support, its goal of minimal
feature sets and extremely fast boot times still encourages you to use a
customized kernel.
> I could trace this to the flag CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES
> being disabled in the default Debian kernel config.
...
> 1) Is there any specific reason for this flag to be disabled in the
> Debian kernel?
It's not generally useful, so it hasn't been deemed appropriate for
inclusion in the standard kernel builds. It'll be up to the kernel team
to decide if supporting Firecracker with the default kernel is a
sufficiently interesting use-case to warrant changing it. IMO, it is
not.
> 2) If the flag is disabled for no specific reason, is there any chance
> for this flag to be enabled in future Debian versions, so the
> virtio_mmio module recognizes the .device parameter by default?
You should open a wishlist severity bug against the src:linux package to
officially request this change.
noah
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