Added * The API `PATCH` methods for `machine-config` can now be used to reset the `cpu_template` to `"None"`. Until this change there was no way to reset the `cpu_template` once it was set. * Added a `rebase-snap` tool for rebasing a diff snapshot over a base snapshot. * Mmds version is persisted across snapshot-restore. Snapshot compatibility is preserved bidirectionally, to and from a Firecracker version that does not support persisting the Mmds version. In such cases, the default V1 option is used. * Added `--mmds-size-limit` for limiting the mmds data store size instead of piggy-backing on `--http-api-max-payload-size`. If left unconfigured it defaults to the value of `--http-api-max-payload-size`, to provide backwards compatibility. * Added optional `mem_backend` body field in `PUT` requests on `/snapshot/load`. This new parameter is an object that defines the configuration of the backend responsible for handling memory loading during snapshot restore. The `mem_backend` parameter contains `backend_type` and `backend_path` required fields. `backend_type` is an enum that can take either `File` or `Uffd` as value. Interpretation of `backend_path` field depends on the value of `backend_type`. If `File`, then the user must provide the path to file that contains the guest memory to be loaded. Otherwise, if `backend_type` is `Uffd`, then `backend_path` is the path to a unix domain socket where a custom page fault handler process is listening and expecting a UFFD to be sent by Firecracker. The UFFD is used to handle the guest memory page faults in the separate process. * Added logging for the snapshot/restore and async block device IO engine features to indicate they are in development preview. Changed * The API `PATCH` method for `/machine-config` can be now used to change `track_dirty_pages` on aarch64. * MmdsV2 is now Generally Available. * MmdsV1 is now deprecated and will be removed in Firecracker v2.0.0. Use MmdsV2 instead. * Deprecated `mem_file_path` body field in `PUT` on `/snapshot/load` request. Fixed * Fixed inconsistency that allowed the start of a microVM from a JSON file without specifying the `vcpu_count` and `mem_size_mib` parameters for `machine-config` although they are mandatory when configuring via the API. Now these fields are mandatory when specifying `machine-config` in the JSON file and when using the `PUT` request on `/machine-config`. * Fixed inconsistency that allowed a user to specify the `cpu_template` parameter and set `smt` to `True` in `machine-config` when starting from a JSON file on aarch64 even though they are not permitted when using `PUT` or `PATCH` in the API. Now Firecracker will return an error on aarch64 if `smt` is set to `True` or if `cpu_template` is specified. * Fixed inconsistent behaviour of the `PUT` method for `/machine-config` that would reset the `track_dirty_pages` parameter to `false` if it was not specified in the JSON body of the request, but left the `cpu_template` parameter intact if it was not present in the request. Now a `PUT` request for `/machine-config` will reset all optional parameters (`smt`, `cpu_template`, `track_dirty_pages`) to their default values if they are not specified in the `PUT` request. * Fixed incosistency in the swagger definition with the current state of the `/vm/config` endpoint.