Added

• Added jailer option --parent-cgroup <relative_path> to allow the placement
  of microvm cgroups in custom cgroup nested hierarchies. The default value is
  <exec-file> which is backwards compatible to the behavior before this
  change.
• Added jailer option --cgroup-version <1|2> to support running the jailer
  on systems that have cgroup-v2. Default value is 1 which means that if
  --cgroup-version is not specified, the jailer will try to create cgroups
  on cgroup-v1 hierarchies only.
• Added --http-api-max-payload-size parameter to configure the maximum payload
  size for PUT and PATCH requests.
• Limit MMDS data store size to --http-api-max-payload-size.
• Cleanup all environment variables in Jailer.
• Added metrics for accesses to deprecated HTTP and command line API endpoints.
• Added permanent HTTP endpoint for GET on /version for getting the
  Firecracker version.
• Added --metadata parameter to enable MMDS content to be supplied from a file
  allowing the MMDS to be used when using --no-api to disable the API server.
• Checksum file for the release assets.
• Added support for custom headers to MMDS requests. Accepted headers are:
  X-metadata-token, which accepts a string value that provides a session
  token for MMDS requests; and X-metadata-token-ttl-seconds, which
  specifies the lifetime of the session token in seconds.
• Support and validation for host and guest kernel 5.10.
• A kernel support policy.
• Added io_engine to the pre-boot block device configuration.
  Possible values: Sync (the default option) or Async (only available for
  kernels newer than 5.10.51). The Async variant introduces a block device
  engine that uses io_uring for executing requests asynchronously, which is in
  developer preview (NOT for production use).
  See docs/api_requests/block-io-engine.md.
• Added block.io_engine_throttled_events metric for measuring the number of
  virtio events throttled because of the IO engine.
• New optional version field to PUT requests towards /mmds/config to
  configure MMDS version. Accepted values are V1 and V2 and default is
  V1. MMDS V2 is developer preview only (NOT for production use) and
  it does not currently work after snapshot load.
• Mandatory network_interfaces field to PUT requests towards
  /mmds/config which contains a list of network interface IDs capable of
  forwarding packets to MMDS.

Changed

• Removed the --node jailer parameter.
• Deprecated vsock_id body field in PUTs on /vsock.
• Removed the deprecated the --seccomp-level parameter.
• GET requests to MMDS require a session token to be provided through
  X-metadata-token header when using V2.
• Allow PUT requests to MMDS in order to generate a session token
  to be used for future GET requests when version 2 is used.
• Remove allow_mmds_requests field from the request body that attaches network
  interfaces. Specifying interfaces that allow forwarding requests to MMDS is done
  by adding the network interface's ID to the network_interfaces field of PUT
  /mmds/config request's body.
• Renamed /machine-config ht_enabled to smt.
• smt field is now optional on PUT /machine-config, defaulting to
  false.
• Configuring smt: true on aarch64 via the API is forbidden.

Fixed

• Fixed incorrect propagation of init parameters in kernel commandline.
  Related to:
  #2709.
• Adapt T2 and C3 CPU templates for kernel 5.10. Firecracker was not previously
  masking some CPU features of the host or emulated by KVM, introduced in more
  recent kernels: umip, vmx, avx512_vnni.
• Fix jailer's cgroup implementation to accept properties that contain multiple
  dots.