Module Mirage

The type for values representing module types.

type t is a value representing the module type t.

Construct a functor type from a type and an existing functor type. This corresponds to prepending a parameter to the list of functor parameters. For example:

kv_ro @-> ip @-> kv_ro

This describes a functor type that accepts two arguments -- a kv_ro and an ip device -- and returns a kv_ro.

The type for values representing module implementations.

m $ a applies the functor m to the module a.

Same as impl but with hidden type.

dep t is the (build-time) dependency towards t.

The type for configure-time command-line arguments.

The type for runtime command-line arguments.

runtime_arg ~pos ?packages v is the runtime argument pointing to the value v. pos is expected to be __POS__. packages specifies in which opam package the value v is defined.

The type for abstract keys.

The type for keys' parsing context. See Key.context.

The type for values parsed from the command-line. See Key.value.

key k is an untyped representation of k.

if_impl v impl1 impl2 is impl1 if v is resolved to true and impl2 otherwise.

match_impl v cases ~default chooses the implementation amongst cases by matching the v's value. default is chosen if no value matches.

The type for opam packages.

Installation scope of a package.

package ~scope ~build ~sublibs ~libs ~min ~max ~pin opam is a package. Build indicates a build-time dependency only, defaults to false. The library name is by default the same as opam, you can specify ~sublibs to add additional sublibraries (e.g. ~sublibs:["mirage"] "foo" will result in the library names ["foo"; "foo.mirage"]. In case the library name is disjoint (or empty), use ~libs. Specifying both ~libs and ~sublibs leads to an invalid argument. Version constraints are given as min (inclusive) and max (exclusive). If pin is provided, a pin-depends is generated, pin_version is "dev" by default. ~scope specifies the installation location of the package.

The type for build information.

main name typ is the functor name, having the module type typ. The connect code will call <name>.start.

• If packages or packages_v is set, then the given packages are installed before compiling the current application.

of_device t is the implementation device t.

impl ~packages ~packages_v ~install ~install_v ~keys ~runtime_args ~extra_deps ~connect ~dune ~configure ~files module_name module_type is an implementation of the device constructed by the arguments. packages and packages_v are the dependencies (where packages_v is inside Key.value). install and install_v are the install instructions (used in the generated opam file), keys are the configuration-time keys, runtime_args the arguments at runtime, extra_deps are a list of extra dependencies (other implementations), connect is the code emitted for initializing the device, dune are dune stanzas added to the build rule, configure are commands executed at the configuration phase, files are files to be added to the list of generated files, module_name is the name of the device module, and module_type is the type of the module.

Configuration keys.

Configuration keys.

For the Qubes target, the Qubes database from which to look up dynamic runtime configuration information.

A default qubes database, guessed from the usual valid configurations.

Abstract type for timers.

Implementations of the Mirage_time.S signature.

The default timer implementation.

Abstract type for POSIX clocks.

Implementations of the Mirage_clock.PCLOCK signature.

The default mirage-clock Mirage_clock.PCLOCK implementation.

Abstract type for monotonic clocks

Implementations of the Mirage_clock.MCLOCK signature.

The default mirage-clock Mirage_clock.MCLOCK implementation.

The type for log reporters.

Implementation of the log reporter type.

default_reporter ?clock ?level () is the log reporter that prints log messages to the console, timestampted with clock. If not provided, the default clock is default_posix_clock. level is the default log threshold. It is Some Logs.Info if not specified.

no_reporter disable log reporting.

Abstract type for random sources.

Implementations of the Mirage_random.S signature.

Default PRNG device to be used in unikernels. It uses getrandom/getentropy on Unix, and a Fortuna PRNG on other targets.

rng () is the device Mirage_crypto_rng.Make.

Abstract type for raw block device configurations.

Implementations of the Mirage_block.S signature.

Use the given file as a raw block device.

Use the given XenStore ID (ex: /dev/xvdi1 or 51760) as a raw block device.

Use a ramdisk with the given name.

Abstract type for read-only key/value store.

Implementations of the Mirage_kv.RO signature.

Crunch a directory. The contents of the directory is transformed into OCaml code, which is then compiled as part of the unikernel.

tar_kv_ro block is a read-only tar archive.

Direct access to the underlying filesystem as a key/value store for Unix. For other backends, this is equivalent to crunch.

Use a FAT formatted block device.

Generic key/value that will choose dynamically between direct_kv_ro and crunch. To use a filesystem implementation, try kv_ro_of_fs.

If no key is provided, a new Key.kv_ro is created with the group argument.

docteur ?mode ?name ?output ?analyze remote is a read-only, key-value store device. Data is stored on that device using the Git PACK file format, version 2. This format has very good compression factors for many similar files of relatively small size. For instance, 14Gb of HTML files can be compressed into a disk image of 240Mb.

Unlike crunch, docteur produces an external image which means that less memory is used to keep and get files. The image can be produced from many sources:

• A local Git repository (like file://path/to/the/git/repository/)
• A simple directory (like file://path/to/a/simple/directory/)
• A remote Git repository (via SSH, HTTP(S) or TCP/IP as what git clone expects)

If you use a Git repository, you can choose a specific branch with the ?branch argument (like refs/heads/main). Otherwise, this argument is ignored.

If you use a simple directory, it can be a relative from your unikernel project (relativize://directory) or an absolute path (file://home/user/directory).

If a required file is produced by a dune rule, you must notice it via the extra_deps argument.

For a Solo5 target, users must attach the image as a block device:

$ solo5-hvt --block:<name>=<path-to-the-image> -- unikernel.{hvt,...}

The user is able to specify the name of the block device (default to "docteur"). The user can also specify the output of docteur.make, the tool which generate the image (default to "disk.img").

For the Unix target, the program open the image at the beginning of the process. An integrity check of the image can be done via the analyze value (defaults to true).

It's possible to use the file-system into 2 modes:

• `Light: any access requires that we reconstruct the path to the requested file. That means that we will need to extract a few additional objects before the extraction of the requested one. `Light does not cache anything in memory but it can be slower if the requested file is deep in the directory structure.
• `Fast: reconstructs and cache the layout of the directory structure when the unikernel starts: it might increase boot-time and bigger memory requirements. However, `Fast allows the device to decode only the requested object so it is faster than the `Light mode.

Abstract type for read-write key/value store.

Implementations of the Mirage_kv.RW signature.

Direct access to the underlying filesystem as a key/value store. Only available on Unix backends.

An in-memory key-value store using mirage-kv-mem.

chamelon ~program_block_size returns a kv_rw filesystem which is an implementation of littlefs in OCaml. The chamelon device expects a block-device.

unikernel.ml:

open Cmdliner

let program_block_size =
  Arg.(value & opt int 16 & info [ "program-block-size" ])

config.ml:

let db =
  let program_block_size =
    Runtime_arg.create ~pos:__POS__ "Unikernel.program_block_size"
  in
  let block = block_of_file "db" in
  chamelon ~program_block_size block
in

For Solo5 targets, you finally can launch the unikernel with:

$ solo5-hvt --block:db=db.img unikernel.hvt

The block-device must be well-formed and formatted by the chamelon tool:

$ dd if=/dev/zero of=db.img bs=1M count=1
$ chamelon format db.img 512

tar_kv_rw block is a read/write tar archive. Note that the filesystem is append-only. That is, files can generally not be removed, set_partial only works on what is allocated, and there are restrictions on rename.

ccm_block key block returns a new block which is a AES-CCM encrypted disk.

Note also that the available size of an encrypted block is always divided by 2 of its real size: a 512M block will only be able to contain 256M data if it is encrypted.

You can either use a fresh block device as encrypted storage. This does not need any preparation, just using ccm_block with the desired key. If you have an existing disk image that you want to encrypt, you can use the ccmblock tool given by the mirage-block-ccm opam package.

$ ccmblock enc -i db.img -k 0x10786d3a9c920d0b3ec80dfaaac557a7 -o edb.img

Accept the key as a runtime argument, in unikernel.ml:

open Cmdliner

let aes_ccm_key =
  let doc = "The key of the block device (hex formatted)" in
  Arg.(required & opt (some string) None & info ~doc [ "aes-ccm-key" ])

Then, into you config.ml, you just need to compose your block device with ccm_block:

let encrypted_block =
  let aes_ccm_key =
    Runtime_arg.create ~pos:__POS__ "Unikernel.aes_ccm_key"
  in
  let block = block_of_file "edb"
  ccm_block aes_ccm_key block
in

Finally, with Solo5, you can launch your unikernel with that:

$ solo5-hvt --block:edb=edb.img \
  --arg="--aes-ccm-key=0x10786d3a9c920d0b3ec80dfaaac557a7" \
  unikernel.hvt

You can finally compose a file-system such as chamelon with this block device (and you have a encrypted file-system!):

let fs = chamelon ~program_block_size encrypted_block

Abstract type for network configurations.

Implementations of the Mirage_net.S signature.

default_network is a dynamic network implementation which attempts to do something reasonable based on the target.

A custom network interface. Exposes a Runtime_arg.interface key.

Implementations of the Ethernet.S signature.

etif net is the ethernet layer on net.

• deprecated Deprecated. Use [ethif] instead.

ethif net is the ethernet layer on net.

Implementation of the Arp.S signature.

ARP implementation provided by the arp library

Abstract type for IP configurations.

The Tcpip.Ip.S module signature with ipaddr = Ipaddr.V4.

The Tcpip.Ip.S module signature with ipaddr = Ipaddr.V6.

The Tcpip.Ip.S module signature with ipaddr = Ipaddr.t.

Types for manual IPv4 configuration.

Types for manual IPv6 configuration.

Use an IPv4 address Exposes the keys Runtime_arg.V4.network and Runtime_arg.V4.gateway. If provided, the values of these keys will override those supplied in the ipv4 configuration record, if that has been provided.

Use a given initialized QubesDB to look up and configure the appropriate * IPv4 interface.

Use an IPv6 address. Exposes the keys Runtime_arg.V6.network, Runtime_arg.V6.gateway.

Implementation of the Tcpip.Udp.S signature.

Implementation of the Tcpip.Tcp.S signature.

Implementation of the Tcpip.Stack.V4V6 signature.

Direct network stack with given ip.

Network stack with sockets.

Build a stackv4v6 by checking the Runtime_arg.V6.network, and Runtime_arg.V6.gateway keys for IPv4 and IPv6 configuration information, filling in unspecified information from ?config, then building a stack on top of that.

Generic stack using a net keys: Key.net.

• If net = host then socket_stackv4v6 is used
• Else, if unix or macosx then socket_stackv4v6 is used
• Else, static_ipv4v6_stack is used.

If a key is not provided, it uses Key.net (with the group argument) to create it.

tcpv4v6 stackv4v6 is an helper to extract the TCP/IP stack regardless the UDP/IP stack expected by some devices such as protocols.

generic_happy_eyeballs stackv4v6 creates a new happy-eyeballs value which is able to connect to a remote host and allocate finally a connected flow from the given network implementation stackv4v6. However, if you want to resolve (DNS resolution) & connect to a remote host, you must complete your unikernel with a generic_dns_client which upgrade the happy-eyeballs stack with a DNS resolution stack.

This device has several optional arguments of keys for timeouts specified in nanoseconds.

generic_dns_client stackv4v6 happy_eyeballs creates a new DNS value which is able to resolve domain-name from nameservers. It requires a network and happy-eyeballs stack to communicate with these nameservers.

The nameservers argument is a list of strings. The format of them is:

• udp:ipaddr(:port)? if you want to communicate with a DNS resolver via UDP
• tcp:ipaddr(:port)? if you want to communicate with a DNS resolver via TCP/IP
• tls:ipaddr(:port)?(!<authenticator>) if you to communicate with a DNS resolver via TLS. You are able to introduce an <authenticator> (please, follow the documentation about X509.Authenticator.of_string to get an explanation of its format). Otherwise, by default, we use trust anchors from NSS' certdata.txt.

Helper for constructing a syslog_config.

The type for syslog

Implementation of the syslog type.

Emit log messages via UDP to the configured host.

Emit log messages via TCP to the configured host.

Emit log messages via TLS to the configured host, using the credentials (private key, certificate, trust anchor) provided in the KV_RO using the keyname.

mimic_happy_eyeballs stackv4v6 happy_eyeballs dns_client creates a device which initiate a global happy-eyeballs loop. By this way, an underlying instance works to initiate a TCP/IP connection from an IP address or a domain-name.

For the domain-name resolution, we ask the happy-eyeballs instance to resolve the given domain-name via its DNS client.

The resulting device can be used and re-used to for any clients which need to initiate a connection (like alpn_client or git_tcp).

cohttp_server starts a Cohttp server.

httpaf_server starts a http/af server.

cohttp_server starts a Cohttp server.

paf_server ~port tcpv4v6 creates an instance which will start to listen on the given port. With this instance and the produced module HTTP_server, the user can initiate:

• a simple HTTP server
• a simple HTTPS server (with a TLS configuration)
• a simple ALPN (http/1.1 & h2) server with TLS

This is a simple example of how to launch an HTTP server: unikernel.ml

open Cmdliner

let port =
  let doc = "Port of the HTTP service." in
  Arg.(value & opt int 8080 & info [ "p"; "port" ])

module Make (HTTP_server : Paf_mirage.S with type ipaddr = Ipaddr.t) =
struct
  let error_handler (_ipaddr, _port) ?request:_ _error _send = ()

  let request_handler :
      HTTP_server.TCP.flow -> Ipaddr.t * int -> Httpaf.Reqd.t -> unit =
   fun _socket (_ipaddr, _port) reqd ->
    let contents = "Hello World!\n" in
    let headers =
      Httpaf.Headers.of_list
        [
          ("content-length", string_of_int (String.length contents));
          ("content-type", "text/plain");
          ("connection", "close");
        ]
    in
    let response = Httpaf.Response.create ~headers `OK in
    Httpaf.Reqd.respond_with_string reqd response contents

  let start http_server port =
    let service =
      HTTP_service.http_service ~error_handler request_handler
    in
    let (`Initialized thread) = HTTP_server.serve service http_server in
    thread
end

config.ml

open Mirage

let port = Runtime_arg.create ~pos:__POS__ "Unikernel.port"
let main = main "Unikernel.Make" (http_server @-> job)
let stackv4v6 = generic_stackv4v6 default_network
let http_server = paf_server ~port (tcpv4v6_of_stackv4v6 stackv4v6)

let () =
  register "main"
    ~runtime_args:[ Runtime_arg.v port ]
    [ main $ http_server ]

Abstract type for ALPN HTTP clients

paf_client tcpv4v6 dns creates an ALPN device which can do HTTP (http/1.1 & h2) requests as a HTTP client. The device allocated represents values required to initiate a connection to HTTP webservers. The user can, then, use the module Http_mirage_client.request to communicate with HTTP webservers. This is an example of how to use the ALPN devices:

unikernel.ml

module Make (HTTP_client : Http_mirage_client.S) = struct
  let start http =
    Http_mirage_client.request http "https://google.com"
      (fun _response buf str -> Buffer.add_string buf str ; Lwt.return buf)
      (Buffer.create 0x100) >>= function
    | Ok (response, buf) ->
      let body = Buffer.contents buf in
      ...
    | Error _ -> ...
end

config.ml

open Mirage

let main = main "Unikernel.Make" (alpn_client @-> job)
let stackv4v6 = generic_stackv4v6 default_network
let he = generic_happy_eyeballs stack
let dns = generic_dns_client stack he

let alpn_client =
  let mimic = mimic_happy_eyeballs stackv4v6 he dns in
  paf_client (tcpv4v6_of_stackv4v6 stackv4v6) mimic

let () = register "main" [ main $ alpn_client ]

default_argv is a dynamic argv implementation which attempts to do something reasonable based on the target.

no_argv Disable command line parsing and set argv to |""|.

The type for devices that implement the Git protocol.

merge_git_clients a b is a device that can connect to remote Git repositories using either the device a or the device b.

git_tcp tcpv4v6 dns is a device able to connect to a remote Git repository using TCP/IP.

git_ssh ?group ?authenticator ?key ?password tcpv4v6 dns is a device able to connect to a remote Git repository using an SSH connection with the given private key or password. The identity of the remote Git repository can be verified using authenticator.

The format of the private key is: <type>:<seed or b64 encoded>. <type> can be rsa or ed25519 and, if the type is RSA, we expect the seed of the private key. Otherwise (if the type is Ed25519), we expect the b64-encoded private key.

The format of the authenticator is SHA256:<b64-encoded-public-key>, the output of:

$ ssh-keygen -lf <(ssh-keyscan -t rsa|ed25519 remote 2>/dev/null)

git_http ?group ?authenticator ?headers tcpv4v6 dns is a device able to connect to a remote Git repository via an HTTP(S) connection, using the provided HTTP headers. The identity of the remote Git repository can be verified using authenticator.

The format of it is:

• none no authentication
• key(:<hash>)?:<b64-encoded fingerprint> to authenticate via the key fingerprint
• cert(:<hash>)?:<b64-encoded fingerprint> to authenticate via the cert fingerprint
• trust-anchor(:<der-encoded cert>)+ to authenticate via a list of certificates
• By default, we use X.509 trust anchors extracted from Mozilla's NSS

job is the combinator for representing main tasks.

noop is a job that does nothing, has no dependency and returns ()

runtime_args argv is a job that loads argv.

register name jobs registers the application named by name which will executes the given jobs.

• parameter reporter

  Configure logging. The default log reporter is default_reporter. To disable logging, use no_reporter.

• parameter argv

  Configure command-line argument parsing. The default parser is default_argv. To disable command-line parsing, use no_argv.