# Major Changes in microvm.nix

## Unreleased: `main` branch

* Shell scripts to setup virtiofsd, interfaces, and PCI devices for
  pass-through have moved from systemd units in the host to the `bin/`
  subdirectory of MicroVM packages. That means you can actually use
  them from the command-line if you would like to run with virtiofsd.

  A breaking change is the move of the `microvm.virtiosd.*` options
  from the host to the microvm NixOS module. They were introduced only
  after 0.5.0.

  New VMs still work on old hosts, but old VMs are missing the
  scripts. Switching your updated NixOS host will print a warning
  about which MicroVMs need updating.

* `bin/virtiofsd-run` (`microvm-virtiofsd@.service`) now starts the
  multiple virtiofsd instances through supervisord.
* The `microvm` module allows configuration of
  `microvm.virtiofsd.group` and
  `microvm.virtiofsd.inodeFileHandles` and
  `microvm.virtiofsd.threadPoolSize` now.
* Per-share virtiofsd options: `microvm.shares.*.posixAcl` and
  `.extraArgs`, enabling per-share UID/GID remapping via
  `--translate-uid` / `--translate-gid`.
* Per-share **DAX** for virtiofs shares: `microvm.shares.*.dax` and
  `.daxWindowSize`, supported on **alioth** and **crosvm**. On crosvm
  such a share bypasses virtiofsd and is served by crosvm's own
  built-in virtio-fs device, so `microvm.virtiofsd.warnOnIgnoredExtraArgs`
  warns about `extraArgs` that no longer apply.
* Add the [alioth VMM](https://github.com/google/alioth)
* Fixes for the stratovirt VMM
* New volume image files will be created with `truncate` instead of
  `fallocate`, saving disk space.
* Building the `microvm.storeDisk` is now faster as the system closure
  is no longer first copied into the build directory. A mount
  namespace is setup with bubblewrap instead. mkfs.erofs can now run
  multi-threaded.
* `microvm.storeDiskErofsFlags` no longer includes `-Ededupe` by
  default, so erofs store disks build multi-threaded by default. This
  results in a much faster build for a slightly larger image.
  `-Efragments` is kept as it is compatible with multi-threading. Add
  `-Ededupe` back to favor small image size over build speed.
* The store disk is now opened with O_DIRECT on crosvm, qemu,
  cloud-hypervisor, kvmtool, and stratovirt to avoid double caching
  in both the host and the guest. Set the new
  `microvm.storeDiskDirect = false` to restore buffered reads.
  Enabling it on an unsupported VMM is an error.

## 0.5.0 (2024-04-06)

* **tap interfaces** are now **multi-queue** when running with more
  than one VCPU. Update your host!
* The `host` module enables **Kernel Samepage Merging** by default.
* **qemu** can run non-native systems by using its **Tiny Code
  Generator** instead of KVM.
* **SSH deployment scripts** are added as
  `config.microvm.deploy.rebuild`
* **qemu** defaults to the *microvm* machine model now as it supports
  PCI, USB, and ACPI by now. Set `microvm.qemu.machine = "q35"` if
  this breaks for you.
* The NixOS **hardened** profile can be used by falling back to
  *squashfs*.
* Runners execute the hypervisor with a process name of
  `microvm@$NAME`
* We no longer let `environment.noXlibs` default to `true`
* **Breaking:** the `microvm` user is no longer in the `disk` group
  for security reasons. Add `users.users.microvm.extraGroups = [
  "disk" ]` to your config to restore the old behavior.

## 0.4.1 (2023-11-03)

* **cloud-hypervisor** replaces **rust-hypervisor-firmware** with
  direct kernel+initramfs loading.
* The microvm module now optimizes the NixOS configuration for size.
* **crosvm** now supports **macvtap** interfaces.
* The option `microvm.qemu.bios` has been dropped again for simplicity
  reasons.

  **qemu** boots fast with the shipped SeaBIOS if after both SATA and
  the network interface option ROM (iPXE) have been disabled.
* `microvm.kernelParams` always copy `boot.kernelParams`
* **firecracker** is no longer launched through **firectl**.
* Networking example documentation has been split into multiple
  scenarios.
* **Vsock** support has been added for Hypervisors that connect them
  to the Linux host's *AF_VSOCK*: qemu, crosvm, and kvmtool.
* Our packages and overlay include the unstable version of
  **waypipe**, featuring **Vsock** support.
* Add support for the old command-line parameter syntax that returned
  with **cloud-hypervisor** 36.0.

## 0.4.0 (2023-07-09)

* Stop building a custom kernel by booting the NixOS kernel with an
  initrd.
* New Hypervisor: **stratovirt** by Huawei
* Support *fully declarative* MicroVMs that are part of the host's
  NixOS configuration. **No Flakes required!**
* We use **squashfs-tools-ng** now.
* The `microvm-console` script has been removed because pty console
  setup was too cumbersome to maintain across all hypervisors.
* `microvm.storeDiskType` defaults to `"erofs"` now for higher runtime
  performance.

## 0.3.3 (2023-05-24)

* Support for **macvtap** network interfaces has been added.
* `boot.initrd.systemd.enable` is now supported.
* Experimental **graphics** support for qemu, and cloud-hypervisor
* **qemu**: use qboot BIOS

## 0.3.2 (2022-12-25)