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μVMs
===
Slowly comprehending [spectrum-os](https://spectrum-os.org) and [microvm.nix](https://github.com/microvm-nix/microvm.nix), by reproducing bits and pieces using [NixOS](https://nixos.org), [systemd](https://nixos.org/manual/nixos/stable/options#opt-systemd.services), and [cloud-hypervisor](https://github.com/cloud-hypervisor/cloud-hypervisor).
Slowly comprehending [spectrum-os](https://spectrum-os.org) and [microvm.nix](https://github.com/microvm-nix/microvm.nix), by reproducing bits and pieces using [NixOS](https://nixos.org) and [cloud-hypervisor](https://github.com/cloud-hypervisor/cloud-hypervisor).
Prior Art
---
### Projects
- Obvious: Qubes, Spectrum, Genode, ...
- Google ChromeOS and [AWS Firecracker](https://firecracker-microvm.github.io):
- rust-vmm, [crosvm](https://crosvm.dev/book), and [sommelier](https://chromium.googlesource.com/chromiumos/platform2/+/master/vm_tools/sommelier);
- [Asahi muvm](https://github.com/AsahiLinux/muvm): microvms using [libkrun](https://github.com/containers/libkrun) and virtio-gpu "native context".
- [AppVM](https://github.com/jollheef/appvm): apparently available in Nixpkgs under `nixos/modules/virtualisation/appvm.nix`. Based on (NixOS,) qemu and libvirt.
- [valpackett/munix](https://git.clan.lol/clan/munix)
- ...
### People
Following the right people is one of the most effective ways to maintain bibliography, a form of "importance sampling".
Following the right people might one of the most effective ways to maintain bibliography, a form of "importance sampling".
The following are the people whose work, at the time of writing, I already know to watch out for. Whom am I missing?
- [Alyssa Ross](https://github.com/alyssais)
- Via [spectrum.org]https://spectrum-os.org/bibliography.html) and [Nixpkgs](https://github.com/NixOS/Nixpkgs).
- [Demi Marie](https://demimarie.github.io):
- Via [spectrum-devel](https://spectrum-os.org/lists/archives/spectrum-devel/2ff17d00-6603-46ae-9eb0-d4fa179db86c@gmail.com/) and Qubes.
- [valpackett](https://val.packett.cool)
- yureka
- [Thomas Leonard](https://roscidus.com/blog/blog/2021/03/07/qubes-lite-with-kvm-and-wayland)
- Via [spectrum-discuss](https://spectrum-os.org/lists/archives/spectrum-discuss/CAG4opy8BZn2pXDRBHOjcENFBHJON1LoG7A8GPdP0Wt_3KLaHyw@mail.gmail.com/), [qubes-lite, and `wayland-proxy-virtwl`](https://roscidus.com/blog/blog/2021/03/07/qubes-lite-with-kvm-and-wayland).
- [Astro](https://spaceboyz.net/~astro/):
@ -25,16 +37,6 @@ The following are the people whose work, at the time of writing, I already know
- Via [Qubes](https://doc.qubes-os.org/en/latest/developer/general/devel-books.html) [OS](https://theinvisiblethings.blogspot.com/2012/09/how-is-qubes-os-different-from.html).
- ...
### Projects
- Obvious: Qubes, Spectrum, Genode, ...
- Google ChromeOS and [AWS Firecracker](https://firecracker-microvm.github.io):
- rust-vmm, [crosvm](https://crosvm.dev/book), and [sommelier](https://chromium.googlesource.com/chromiumos/platform2/+/master/vm_tools/sommelier);
- [Asahi muvm](https://github.com/AsahiLinux/muvm): microvms using [libkrun](https://github.com/containers/libkrun) and virtio-gpu "native context".
- [AppVM](https://github.com/jollheef/appvm): apparently available in Nixpkgs under `nixos/modules/virtualisation/appvm.nix`. Based on (NixOS,) qemu and libvirt.
- ...
### Timeline
The following are the questions I'd like to eventually answer about how virtualization happened:
@ -76,7 +78,10 @@ The following are some of the current "am I holding this right?" questions:
- [ ] Filesystems:
Virtio-blk appears to be the way to allocate persistent storage for VMs that require it.
In practice this means allocating a zvol or a contiguous file on the hypervisor,
The alternative is virtiofsd, which is potentially more RAM-hungry, and which significantly
limits bandwidth at least when used with explicitly enabling DAX (`microvm.nix`).
In practice the virtio-blk way means allocating a zvol or a contiguous file on the hypervisor,
to be exposed to the guest as a block device. One suspicion I have is that allocating
a CoW filesystem (e.g. xfs, btrfs) on top of another CoW filesystem (e.g. zfs, as in xfs-on-zvol) may have non-trivial
implications for fragmentation, depending on parameters like the chunksizes.
@ -88,14 +93,13 @@ The following are some of the current "am I holding this right?" questions:
#### `spectrum-os`
...is in active development and not advertised as user-ready yet.
Spectrum OS appears to be a balance-shifting project, building up towards a principled solution, which must require patience...
It does not, for example, reuse NixOS systemd modules, but uses s6 instead.
Yes. Soon.
#### `microvm.nix`
Is inherently static.
A cynical spin on `microvm.nix` would be, and I mean it with utmost respect, that it's a glorified qemu flags generator, written in Nix.
A cynical spin on `microvm.nix` would be, and I mean it with utmost respect, that it's a glorified qemu flags generator, written in Nix,
and Nix is slow.
When using `microvm.nix` you write, for example, each TAP's `hwaddr` by hand, and then rebuild the "runner script".
When using the "fully-declarative mode" you also engangle the guest's and the hypervisor's life cycles, and double the NixOS evaluation time.
Microvm-nix ships support for a wide selection of different hypervisors, but you may only care about e.g. `cloud-hypervisor`.
@ -105,3 +109,5 @@ An instructive reference implementation and a convenient entry point, `microvm.n
I only noticed the option in `man configuration.nix` a few days ago,
so I just never tried. Long-term I'd definitely prefer not to use qemu.
The golang tool relies on obscure Nix CLI options and "channels" (as in tarballs).