# Changelog

## [0.22.2]

### Fixed

 - Fixed inconsistency in YAML file InstanceInfo definition
 
## [0.22.1]

### Fixed

 - Limited serial device buffer size to maximum 64 bytes. 
 
## [0.22.0]

### Added

- Added a new API call, `PUT /metrics`, for configuring the metrics system.
- Added `app_name` field in InstanceInfo struct for storing the application
  name.
- New command-line parameters for `firecracker`, named `--log-path`,
  `--level`, `--show-level` and `--show-log-origin` that can be used
  for configuring the Logger when starting the process. When using
  this method for configuration, only `--log-path` is mandatory.
- Added a [guide](docs/devctr-image.md) for updating the dev container image.
- Added a new API call, `PUT /mmds/config`, for configuring the
  `MMDS` with a custom valid link-local IPv4 address.
- Added experimental JSON response format support for MMDS guest applications
  requests.
- Added metrics for the vsock device. 
- Added devtool strip command which removes debug symbols from the release
- Added the `tx_malformed_frames` metric for the virtio net device, emitted
  when a TX frame missing the VNET header is encountered.

### Fixed

- Added `--version` flag to both Firecracker and Jailer.
- Return `405 Method Not Allowed` MMDS response for non HTTP `GET` MMDS
  requests originating from guest.
- Fixed folder permissions in the jail (#1802).
- Any number of whitespace characters are accepted after ":" when parsing HTTP
  headers.
- Potential panic condition caused by the net device expecting to find a VNET
  header in every frame.
- Potential crash scenario caused by "Content-Length" HTTP header field
  accepting negative values.
- Fixed #1754 - net: traffic blocks when running ingress UDP performance tests
  with very large buffers.

### Changed
- Updated CVE-2019-3016 mitigation information in
  [Production Host Setup](docs/prod-host-setup.md)
- In case of using an invalid JSON as a 'config-file' for Firecracker,
  the process will exit with return code 152.
- Removed the `testrun.sh` wrapper.
- Removed `metrics_fifo` field from the logger configuration.
- Renamed `log_fifo` field from LoggerConfig to `log_path` and
  `metrics_fifo` field from MetricsConfig to `metrics_path`.
- `PATCH /drives/{id}` only allowed post-boot. Use `PUT` for pre-boot
  updates to existing configurations.
- `PATCH /network-interfaces/{id}` only allowed post-boot. Use `PUT` for
  pre-boot updates to existing configurations.
- Changed returned status code from `500 Internal Server Error` to
  `501 Not Implemented`, for queries on the MMDS endpoint in IMDS format, when
  the requested resource value type is unsupported.
- Allowed the MMDS data store to be initialized with all supported JSON types.
  Retrieval of these values within the guest, besides String, Array, and
  Dictionary, is only possible in JSON mode.
- `PATCH` request on `/mmds` before the data store is initialized returns 
  `403 BadRequest`.
- Segregated MMDS documentation in MMDS design documentation and MMDS user
  guide documentation.

## [0.21.0]

### Added

- Support for booting with an initial RAM disk image. This image can be
  specified through the new `initrd_path` field of the `/boot-source` API
  request.

### Fixed

- Fixed #1469 - Broken GitHub location for Firecracker release binary.
- The jailer allows changing the default api socket path by using the extra
  arguments passed to firecracker.
- Fixed #1456 - Occasional KVM_EXIT_SHUTDOWN and bad syscall (14) during 
  VM shutdown.
- Updated the production host setup guide with steps for addressing
  CVE-2019-18960.
- The HTTP header parsing is now case insensitive.
- The `put_api_requests` and `patch_api_requests` metrics for net devices were
  un-swapped.

### Changed
  
- Removed redundant `--seccomp-level` jailer parameter since it can be
  simply forwarded to the Firecracker executable using "end of command
  options" convention.
- Removed `memory.dirty_pages` metric.
- Removed `options` field from the logger configuration.
- Decreased release binary size by ~15%.
- Changed default API socket path to `/run/firecracker.socket`. This path
  also applies when running with the jailer.
- Disabled KVM dirty page tracking by default.
- Removed redundant RescanBlockDevice action from the /actions API.
  The functionality is available through the PATCH /drives API.
  See `docs/api_requests/patch-block.md`.

## [0.20.0]

### Added

- Added support for GICv2.

### Fixed

- Fixed CVE-2019-18960 - Fixed a logical error in bounds checking performed 
  on vsock virtio descriptors.
- Fixed #1283 - Can't start a VM in AARCH64 with vcpus number more than 16.
- Fixed #1088 - The backtrace are printed on `panic`, no longer causing a 
  seccomp fault.
- Fixed #1375 - Change logger options type from Value to Vec<LogOption> to
  prevent potential unwrap on None panics.
- Fixed #1436 - Raise interrupt for TX queue used descriptors
- Fixed #1439 - Prevent achieving 100% cpu load when the net device rx is 
  throttled by the ratelimiter
- Fixed #1437 - Invalid fields in rate limiter related API requests are 
  now failing with a proper error message.
- Fixed #1316 - correctly determine the size of a virtio device backed 
  by a block device.
- Fixed #1383 - Log failed api requests.

### Changed

- Decreased release binary size by 10%.

## [0.19.0]

### Added

- New command-line parameter for `firecracker`, named `--no-api`, which
  will disable the API server thread. If set, the user won't be able to send
  any API requests, neither before, nor after the vm has booted. It must be
  paired with `--config-file` parameter. Also, when API server is disabled,
  MMDS is no longer available now.
- New command-line parameter for `firecracker`, named `--config-file`, which
  represents the path to a file that contains a JSON which can be used for
  configuring and starting a microVM without sending any API requests.
- The jailer adheres to the "end of command options" convention, meaning
  all parameters specified after `--` are forwarded verbatim to Firecracker.
- Added `KVM_PTP` support to the recommended guest kernel config.
- Added entry in FAQ.md for Firecracker Guest timekeeping.

### Changed

- Vsock API call: `PUT /vsocks/{id}` changed to `PUT /vsock` and no longer
  appear to support multiple vsock devices. Any subsequent calls to this API
  endpoint will override the previous vsock device configuration.
- Removed unused 'Halting' and 'Halted' instance states.
- Vsock host-initiated connections now implement a trivial handshake protocol.
  See the [vsock doc](docs/vsock.md#host-initiated-connections) for details.
  Related to:
  [#1253](https://github.com/firecracker-microvm/firecracker/issues/1253),
  [#1432](https://github.com/firecracker-microvm/firecracker/issues/1432),
  [#1443](https://github.com/firecracker-microvm/firecracker/pull/1443)

### Fixed

- Fixed serial console on aarch64 (GitHub issue #1147).
- Upon panic, the terminal is now reset to canonical mode.
- Explicit error upon failure of vsock device creation.
- The failure message returned by an API call is flushed in the log FIFOs.
- Insert virtio devices in the FDT in order of their addresses sorted from
  low to high.
- Enforce the maximum length of the network interface name to be 16 chars as
  specified in the Linux Kernel.
- Changed the vsock property `id` to `vsock_id` so that the API client can be
  successfully generated from the swagger definition.

## [0.18.0]

### Added

- New device: virtio-vsock, backed by Unix domain sockets (GitHub issue #650).
  See `docs/vsock.md`.

### Changed

- No error is thrown upon a flush metrics intent if logger has not been
  configured.

### Fixed

- Updated the documentation for integration tests.
- Fixed high CPU usage before guest network interface is brought up (GitHub
  issue #1049).
- Fixed an issue that caused the wrong date (month) to appear in the log.
- Fixed a bug that caused the seccomp filter to reject legit syscalls in some
  rare cases (GitHub issue #1206).
- Docs: updated the production host setup guide.
- Docs: updated the rootfs and kernel creation guide.

### Removed

- Removed experimental support for vhost-based vsock devices.

## [0.17.0]

### Added

- New API call: `PATCH /machine-config/`, used to update VM configuration,
  before the microVM boots.
- Added an experimental swagger definition that includes the specification for
  the vsock API call.
- Added a signal handler for `SIGBUS` and `SIGSEGV` that immediately terminates
  the process upon intercepting the signal.
- Added documentation for signal handling utilities.
- Added [alpha] aarch64 support.
- Added metrics for successful read and write operations of MMDS, Net and Block
  devices.

### Changed

- `vcpu_count`, `mem_size_mib` and `ht_enabled` have been changed to be mandatory
  for `PUT` requests on `/machine-config/`.
- Disallow invalid seccomp levels by exiting with error.

### Fixed

- Incorrect handling of bind mounts within the jailed rootfs.
- Corrected the guide for `Alpine` guest setup.

## [0.16.0]

### Added

- Added [alpha] AMD support.
- New `devtool` command: `prepare_release`. This updates the Firecracker
  version, crate dependencies and credits in preparation for a new release.
- New `devtool` command: `tag`. This creates a new git tag for the specified
  release number, based on the changelog contents.
- New doc section about building with glibc.

### Changed

- Dropped the JSON-formatted `context` command-line parameter from Firecracker
  in favor of individual classic command-line parameters.
- When running with `jailer` the location of the API socket has changed to
  `<jail-root-path>/api.socket` (API socket was moved _inside_ the jail).
- `PUT` and `PATCH` requests on `/mmds` with data containing any value type
  other than `String`, `Array`, `Object` will returns status code 400.
- Improved multiple error messages.
- Removed all kernel modules from the recommended kernel config.

### Fixed

- Corrected the seccomp filter when building with glibc.

### Removed

- Removed the `seccomp.bad_syscalls` metric.

## [0.15.2]

### Fixed

- Corrected the conditional compilation of the seccomp rule for `madvise`.

## [0.15.1]

### Fixed

- A `madvise` call issued by the `musl` allocator was added to the seccomp
  whitelist to prevent Firecracker from terminating abruptly when allocating
  memory in certain conditions.

## [0.15.0]

### Added

- New API action: SendCtrlAltDel, used to initiate a graceful shutdown,
  if the guest has driver support for i8042 and AT Keyboard. See
  [the docs](docs/api_requests/actions.md#sendctrlaltdel) for details.
- New metric counting the number of egress packets with a spoofed MAC:
  `net.tx_spoofed_mac_count`.
- New API call: `PATCH /network-interfaces/`, used to update the rate limiters
  on a network interface, after the start of a microVM.

### Changed

- Added missing `vmm_version` field to the InstanceInfo API swagger
  definition, and marked several other mandatory fields as such.
- New default command line for guest kernel:
  `reboot=k panic=1 pci=off nomodules 8250.nr_uarts=0
  i8042.noaux i8042.nomux i8042.nopnp i8042.dumbkbd`.

### Fixed

- virtio-blk: VIRTIO_BLK_T_FLUSH now working as expected.
- Vsock devices can be attached when starting Firecracker using the jailer.
- Vsock devices work properly when seccomp filtering is enabled.

## [0.14.0]

### Added

- Documentation for development environment setup on AWS in
  `dev-machine-setup.md`.
- Documentation for microVM networking setup in `docs/network-setup.md`.
- Limit the maximum supported vCPUs to 32.

### Changed

- Log the app version when the `Logger` is initialized.
- Pretty print panic information.
- Firecracker terminates with exit code 148 when a non-whitelisted syscall
  is intercepted.

### Fixed

- Fixed build with the `vsock` feature.

## [0.13.0]

### Added

- Documentation for Logger API Requests in `docs/api_requests/logger.md`.
- Documentation for Actions API Requests in `docs/api_requests/actions.md`.
- Documentation for MMDS in `docs/mmds.md`.
- Flush metrics on request via a PUT `/actions` with the `action_type`
  field set to `FlushMetrics`.

### Changed

- Updated the swagger definition of the `Logger` to specify the required fields
  and provide default values for optional fields.
- Default `seccomp-level` is `2` (was previously 0).
- API Resource IDs can only contain alphanumeric characters and underscores.

### Fixed

- Seccomp filters are now applied to all Firecracker threads.
- Enforce minimum length of 1 character for the jailer ID.
- Exit with error code when starting the jailer process fails.

### Removed

- Removed `InstanceHalt` from the list of possible actions.

## [0.12.0]

### Added

- The `/logger` API has a new field called `options`. This is an array of
  strings that specify additional logging configurations. The only supported
  value is `LogDirtyPages`.
- When the `LogDirtyPages` option is configured via `PUT /logger`, a new metric
  called `memory.dirty_pages` is computed as the number of pages dirtied by the
  guest since the last time the metric was flushed.
- Log messages on both graceful and forceful termination.
- Availability of the list of dependencies for each commit inside the code
  base.
- Documentation on vsock experimental feature and host setup recommendations.

### Changed

- `PUT` requests on `/mmds` always return 204 on success.
- `PUT` operations on `/network-interfaces` API resources no longer accept
  the previously required `state` parameter.
- The jailer starts with `--seccomp-level=2` (was previously 0) by default.
- Log messages use `anonymous-instance` as instance id if none is specified.

### Fixed

- Fixed crash upon instance start on hosts without 1GB huge page support.
- Fixed "fault_message" inconsistency between Open API specification and code
  base.
- Ensure MMDS compatibility with C5's IMDS implementation.
- Corrected the swagger specification to ensure `OpenAPI 2.0` compatibility.

## [0.11.0]

### Added

- Apache-2.0 license
- Docs:
  - [charter](CHARTER.md)
  - [contribution guildelines](CONTRIBUTE.md)
  - [design](docs/design.md)
  - [getting started guide](docs/getting-started.md)
  - [security policy](SECURITY-POLICY.md)
  - [specifications](SPECIFICATION.md)
- **Experimental** vhost-based vsock implementation.

### Changed

- Improved MMDS network stack performance.
- If the logging system is not yet initialized (via `PUT /logger`), log events
  are now sent to stdout/stderr.
- Moved the `instance_info_fails` metric under `get_api_requests`
- Improved [readme](README.md) and added links to more detailed information,
  now featured in subject-specific docs.

### Fixed

- Fixed bug in the MMDS network stack, that caused some RST packets to be sent
  without a destination.
- Fixed bug in `PATCH /drives`, whereby the ID in the path was not checked
  against the ID in the body.

## [0.10.1]

### Fixed

- The Swagger definition was corrected.

## [0.10.0]

### Added

- Each Firecracker process has an associated microVM Metadata Store (MMDS). Its
  contents can be configured using the `/mmds` API resource.

### Changed

- The boot source is specified only with the `kernel_image_path` and
  the optional parameter `boot_args`. All other fields are removed.
- The `path_on_host` property in the drive specification is now marked as
  *mandatory*.
- PATCH drive only allows patching/changing the `path_on_host` property.
- All PUT and PATCH requests return the status code 204.
- CPUID brand string (aka model name) now includes the host CPU frequency.
- API requests which add guest network interfaces have an additional parameter,
  `allow_mmds_requests` which defaults to `false`.
- Stopping the guest (e.g. using the `reboot` command) also terminates the
  Firecracker process. When the Firecracker process ends for any reason,
  (other than `kill -9`), metrics are flushed at the very end.
- On startup `jailer` closes all inherited file descriptors based on
  `sysconf(_SC_OPEN_MAX)` except input, output and error.
- The microVM ID prefixes each Firecracker log line. This ID also appears
  in the process `cmdline` so it's now possible to `ps | grep <ID>` for it.

## [0.9.0]

### Added

- Seccomp filtering is configured via the `--seccomp-level` jailer parameter.
- Firecracker logs the starting addresses of host memory areas provided as
  guest memory slots to KVM.
- The metric `panic_count` gets incremented to signal that a panic has
  occurred.
- Firecracker logs a backtrace when it crashes following a panic.
- Added basic instrumentation support for measuring boot time.

### Changed

- `StartInstance` is a synchronous API request (it used to be an asynchronous
  request).

### Fixed

- Ensure that fault messages sent by the API have valid JSON bodies.
- Use HTTP response code 500 for internal Firecracker errors, and 400 for user
  errors on InstanceStart.
- Serialize the machine configuration fields to the correct data types (as
  specified in the Swagger definition).
- NUMA node assignment is properly enforced by the jailer.
- The `is_root_device` and `is_read_only` properties are now marked as required
  in the Swagger definition of `Drive` object properties.

### Removed

- `GET` requests on the `/actions` API resource are no longer supported.
- The metrics associated with asynchronous actions have been removed.
- Remove the `action_id` parameter for `InstanceStart`, both from the URI and
  the JSON request body.

## [0.8.0]

### Added

- The jailer can now be configured to enter a preexisting network namespace,
  and to run as a daemon.
- Enabled PATCH operations on `/drives` resources.

## Changed

- The microVM `id` supplied to the jailer may now contain alphanumeric
  characters and hyphens, up to a maximum length of 64 characters.
- Replaced the `permissions` property of `/drives` resources with a boolean.
- Removed the `state` property of `/drives` resources.

## [0.7.0]

### Added

- Rate limiting functionality allows specifying an initial one time
  burst size.
- Firecracker can now boot from an arbitrary boot partition by specifying
  its unique id in the driver's API call.
- Block device rescan is triggered via a PUT `/actions` with the drive ID in
  the action body's `payload` field and the `action_type` field set to
  `BlockDeviceRescan`.

### Changed

- Removed `noapic` from the default guest kernel command line.
- The `action_id` parameter is no longer required for synchronous PUT requests
  to `/actions`.
- PUT requests are no longer allowed on `/drives` resources after the guest
  has booted.

### Fixed

- Fixed guest instance kernel loader to accelerate vCPUs launch and
  consequently guest kernel boot.
- Fixed network emulation to improve IO performance.

## [0.6.0]

### Added

- Firecracker uses two different named pipes to record human readable logs and
  metrics, respectively.

### Changed

- Seccomp filtering can be enabled via setting the `USE_SECCOMP` environment
  variable.
- It is possible to supply only a partial specification when attaching a rate
  limiter (i.e. just the bandwidth or ops parameter).
- Errors related to guest network interfaces are now more detailed.

### Fixed

- Fixed a bug that was causing Firecracker to panic whenever a `PUT` request
  was sent on an existing network interface.
- The `id` parameter of the `jailer` is required to be an RFC 4122-compliant
  UUID.
- Fixed an issue which caused the network RX rate limiter to be more
  restrictive than intended.
- API requests which contain unknown fields will generate an error.
- Fixed an issue related to high CPU utilization caused by improper `KVM PIT`
  configuration.
- It is now possible to create more than one network tun/tap interface inside a
  jailed Firecracker.

## [0.5.0]

### Added

- Added metrics for API requests, VCPU and device actions for the serial
  console (`UART`), keyboard (`i8042`), block and network devices. Metrics are
  logged every 60 seconds.
- A CPU features template for C3 is available, in addition to the one for T2.
- Seccomp filters restrict Firecracker from calling any other system calls than
  the minimum set it needs to function properly. The filters are enabled by
  setting the `USE_SECCOMP` environment variable to 1 before running
  Firecracker.
- Firecracker can be started by a new binary called `jailer`. The jailer takes
  as command line arguments a unique ID, the path to the Firecracker binary,
  the NUMA node that Firecracker will be assigned to and a `uid` and `gid` for
  Firecracker to run under. It sets up a `chroot` environment and a `cgroup`,
  and calls exec to morph into Firecracker.

### Changed

- In case of failure, the metrics and the panic location are logged before
  aborting.
- Metric values are reset with every flush.
- `CPUTemplate` is now called `CpuTemplate` in order to work seamlessly with
  the swagger code generator for Go.
- `firecracker-beta.yaml` is now called `firecracker.yaml`.

### Fixed

- Handling was added for several untreated KVM exit scenarios, which could have
  led to panic.
- Fixed a bug that caused Firecracker to crash when attempting to disable the
  `IA32_DEBUG_INTERFACE MSR` flag in the T2 CPU features.

### Removed

- Removed a leftover file generated by the logger unit tests.
- Removed `firecracker-v1.0.yaml`.

## [0.4.0]

### Added

- The CPU Template can be set with an API call on `PUT /machine-config`. The
  only available template is T2.
- Hyperthreading can be enabled/disabled with an API call on
  `PUT /machine-config`. By default, hyperthreading is disabled.
- Added boot time performance test (`tests/performance/test_boottime.py`).
- Added Rate Limiter for VirtIO/net and VirtIO/net devices. The Rate Limiter
  uses two token buckets to limit rate on bytes/s and ops/s. The rate limiter
  can be (optionally) configured per drive with a `PUT` on `/drives/{drive_id}`
  and per network interface with a `PUT` on `/network-interface/{iface_id}`.
- Implemented pre-boot PUT updates for `/boot-source`, `/drives`,
  `/network-interfaces` and `/vsock`.
- Added integration tests for `PUT` updates.

### Changed

- Moved the API definition (`swagger/firecracker-beta.yaml`) to the
  `api_server` crate.
- Removed `"console=ttyS0"` and added `"8250.nr_uarts=0"` to the default kernel
  command line to decrease the boot time.
- Changed the CPU topology to have all logical CPUs on a single socket.
- Removed the upper bound on CPU count as with musl there is no good way to get
  the total number of logical processors on a host.
- Build time tests now print the full output of commands.
- Disabled the Performance Monitor Unit and the Turbo Boost.
- Check the expected KVM capabilities before starting the VM.
- Logs now have timestamps.

### Fixed

- `testrun.sh` can run on platforms with more than one package manager by
  setting the package manager via a command line parameter (`-p`).
- Allow correct set up of multiple network-interfaces with auto-generated MAC.
- Fixed sporadic bug in VirtIO which was causing lost packages.
- Don't allow `PUT` requests with empty body on `/machine-config`.
- Deny `PUT` operations after the microvm boots (exception: the temporarily fix
  for live resize of block devices).

### Removed

- Removed examples crate. This used to have a Python example of starting
  Firecracker. This is replaced by `test_api.py` integration tests.
- Removed helper scripts for getting coverage and coding style errors. These
  were replaced by `test_coverage.py` and `test_style.py` test integration
  tests.
- Removed `--vmm-no-api` command line option. Firecracker can only be started
  via the API.

## [0.3.0]

### Added

- Users can interrogate the Machine Configuration (i.e. vcpu count and memory
  size) using a `GET` request on `/machine-config`.
- The logging system can be configured through the API using a `PUT` on
  `/logger`.
- Block devices support live resize by calling `PUT` with the same parameters
  as when the block was created.
- Release builds have Link Time Optimization (LTO) enabled.
- Firecracker is built with `musl`, resulting in a statically linked binary.
- More in-tree integration tests were added as part of the continuous
  integration system.

### Changed

- The vcpu count is enforced to `1` or an even number.
- The Swagger definition of rate limiters was updated.
- Syslog-enabled logs were replaced with a host-file backed mechanism.

### Fixed

- The host topology of the CPU and the caches is not leaked into the microvm
  anymore.
- Boot time was improved by advertising the availability of the TSC deadline
  timer.
- Fixed an issue which prevented Firecracker from working on 4.14 (or newer)
  host kernels.
- Specifying the MAC address for an interface through the API is optional.

### Removed

- Removed support for attaching vsock devices.
- Removed support for building Firecracker with glibc.

## [0.2.0]

### Added

- Users can now interrogate Instance Information (currently just instance
  state) through the API.

### Changed

- Renamed `api/swagger/all.yaml` to `api/swagger/firecracker-v1.0.yaml` which
  specifies targeted API support for Firecracker v1.0.
- Renamed `api/swagger/firecracker-v0.1.yaml` to
  `api/swagger/firecracker-beta.yaml` which specifies the currently supported
  API.
- Users can now enforce that an emulated block device is read-only via the API.
  To specify whether a block device is read-only or read-write, an extra
  "permissions" field was added to the Drive definition in the API. The root
  filesystem is automatically mounted in the guest OS as `ro`/`rw` according to
  the specified "permissions". It's the responsibility of the user to mount any
  other read-only block device as such within the guest OS.
- Users can now stop the guest VM using the API. Actions of type `InstanceHalt`
  are now supported via the API.

### Fixed

- Added support for `getDeviceID()` in `virtIO-block`. Without this, the guest
  Linux kernel would complain at boot time that the operation is unsupported.
- `stdin` control is returned to the Firecracker process when guest VM is
  inactive. Raw mode `stdin` is forwarded to the guest OS when guest VM is
  running.

### Removed

- Removed `api/swagger/actions.yaml`.
- Removed `api/swagger/devices.yaml`.
- Removed `api/swagger/firecracker-mvp.yaml`.
- Removed `api/swagger/limiters.yaml`.

## [0.1.1]

### Changed

- Users can now specify the MAC address of a guest network interface via the
  `PUT` network interface API request. Previously, the guest MAC address
  parameter was ignored.

### Fixed

- Fixed a guest memory allocation issue, which previously led to a potentially
  significant memory chunk being wasted.
- Fixed an issue which caused compilation problems, due to a compatibility
  breaking transitive dependency in the tokio suite of crates.

## [0.1.0]

### Added

- One-process virtual machine manager (one Firecracker per microVM).
- RESTful API running on a unix socket. The API supported by v0.1 can be found
  at `api/swagger/firecracker-v0.1.yaml`.
- Emulated keyboard (`i8042`) and serial console (`UART`). The microVM serial
  console input and output are connected to those of the Firecracker process
  (this allows direct console access to the guest OS).
- The capability of mapping an existing host tun-tap device as a VirtIO/net
  device into the microVM.
- The capability of mapping an existing host file as a GirtIO/block device into
  the microVM.
- The capability of creating a VirtIO/vsock between the host and the microVM.
- Default demand fault paging & CPU oversubscription.
