Hello MirageOS World

First, make sure you have followed the installation instructions to get a working MirageOS installation. The examples below are in the mirage-skeleton repository. Begin by cloning and changing directory to it:

$ git clone https://github.com/mirage/mirage-skeleton.git
$ cd mirage-skeleton

The mirage-skeleton repository classifies its examples into three groups. This document refers to unikernels in the tutorial directory.

Note: Before we begin, if you aren't familiar with the Lwt library (and the >>= operator it provides), you may want to read at least the start of the Lwt tutorial first.

Additional note: Throughout the tutorial, we'll use mirage configure -t unix to demonstrate building MirageOS applications. If you're using a macOS machine, you should use mirage configure -t macosx instead.

Step 0: Doing Nothing!

Before we try and do anything complicated, let's build a unikernel that starts and then exits, without doing anything else. The code for this is, as you might hope, fairly short. Before we can build our noop unikernel, we must define its configuration telling Mirage what jobs the unikernel is to run. In this example we define a unikernel with zero jobs by passing the empty list. We do this by writing a config.ml file:

$ cat tutorial/noop/config.ml
let () = Mirage.register "noop" []

Finally, we declare the entry point to OCaml in the usual way (let () = ...), registering our unikernel entry points (in this case the empty list) and with a name of the unikernel("noop" in this case) we will build.

Building our unikernel is then simply a matter of:

Evaluating its configuration:
```
$ cd tutorial/noop
$ mirage configure -t unix
```
This step will generate a number of build configuration files, including a Makefile defining targets that we will use in the next step.
Installing dependencies:
```
$ make depends
```
The depends target in the generated Makefile will run commands to:
- Resolve the unikernel dependencies and generates a lockfile.
- Install the build tools in the opam switch.
- install external dependencies of the unikernel dependencies (another set of potential build tools).
- Fetch unikernel dependencies.
NOTE: while performing the lock step, an additional repository https://github.com/mirage/opam-overlays.git is added in your opam switch. This repository contains packages that have been changed to use the dune build system. The --extra-repo argument in mirage configure changes the additional repository to use. --no-extra-repo can be used to disable the extra repository, but the lock step might fail because of dependencies that are not using the dune build system.
Compiling:
```
$ make build
```

You can combine steps (2) and (3) by running the default make target:

$ make

Because we set the configuration target to be Unix (the -t unix argument to the mirage configure command), the result is a standard Unix ELF located in dist/noop that can be executed:

$ dist/noop
$ echo $?
0

Congratulations! You've just built and run your very first unikernel!

Step 1: Hello World!

Except for the noop example above, all unikernels have at least one job. A job is a module with a start function as entrypoint that performs some task. Most jobs will depend on some system devices which they use to interact with the environment. This tutorial will cover examples timer devices, key-value stores, block devies and network interfaces. In this section, we illustrate how to define a unikernel with a job that depends on a timer device.

Mirage unikernels use functors to specify abstract device dependencies that are not dependent on the particular details of an environment. In OCaml, a functor is a module that takes other modules as parameters. Functors are used widely throughout Mirage and we will explain the basic idea and provide examples in this tutorial. For a proper introduction into the core concepts, you may see Real World OCaml, Ch.9 (and also Ch.10, First-Class Modules).

Functors act as functions from modules to modules. They allow us to pass dependencies into a unikernel, so that the program running inside can interact with the environment (read files, send packets, etc) without needing to care whether it will eventually be built to target Unix, Xen, KVM, or something else entirely. The modules that are passed into the unikernel in this way must satisfy type signatures that are specified when the unikernel job value is created in the config.ml file.

In this section, we present a simple example of a unikernel that uses a functor to depend on a device for reading the system's time. We will build and run the MirageOS "Hello World" unikernel that prints a log message with the word hello, sleeps for 1 second, and repeats this 4 times before finally terminating. The output will look like this:

2017-02-08 09:54:44 -01:00: INF [application] hello
2017-02-08 09:54:45 -01:00: INF [application] hello
2017-02-08 09:54:46 -01:00: INF [application] hello
2017-02-08 09:54:47 -01:00: INF [application] hello

Let's start by looking at the code:

$ cat hello/unikernel.ml
open Lwt.Infix

module Hello (Time : Mirage_time.S) = struct
  let start _time =
    let rec loop = function
      | 0 -> Lwt.return_unit
      | n ->
          Logs.info (fun f -> f "hello");
          Time.sleep_ns (Duration.of_sec 1) >>= fun () ->
          loop (n-1)
    in
    loop 4

end

We define a main Hello module parameterised by a module Time, of type Mirage_time.S. The Time module provides the functionality enabling us to interact with the environment clock. Our start function, which is the entrypoint of the job, also takes a parameter _time (an instance of a time which is ignored). This parameterization of a unikernel's main module and its start function is the basic structure required to make a MirageOS unikernel that can be built to run on any supported environment, rather than a standard OCaml POSIX application.

The module type for our Time module, Mirage_time.S, is defined in an external package mirage-time. The name pattern Foo.S for "the signature of Foo modules" is a common OCaml convention (comparable to naming the most-used type in a module t). There are many packages defining module types for use in Mirage.

The concrete implementation of Time will be supplied at compile time, depending on the target that you are compiling for. This calls for some additional configuration in config.ml, so let's take a look:

$ cat tutorial/hello/config.ml
open Mirage

let main =
  main "Unikernel.Hello" (time @-> job) ~packages:[ package "duration" ]

let () = register "hello" [ main $ default_time ]

First we open the Mirage module to save on typing. Next, we define a value main. This name is only a convention, and you should feel free to change it if you wish. main calls the Mirage.main function, passing two parameters. The first is a string declaring the module name that contains our entry point — in this case, standard OCaml compilation behaviour means that the unikernel.ml file produces a module named Unikernel. Again, there's nothing special about this name, and if you want to use something else here, simply rename unikernel.ml accordingly. The @-> combinator is used to add a device driver to the list of functor arguments in the job definition and the final value of this combinator should always be a job. The named argument ~packages defines extra OCaml package dependencies that the job depends on. In this case we depend on the duration library for converting from seconds to nanoseconds.

Notice that we refer to the module name as a string ("Unikernel.Hello") when calling main, instead of directly as an OCaml value. The mirage command-line tool evaluates this configuration file at build time and outputs a main.ml that has the concrete values filled in for you depending on which target you selected during configuration (e.g. Unix or Xen).

MirageOS mirrors the unikernel model on Unix as far as possible: your application is built as a unikernel which needs to be instantiated and run whether on Unix or on a hypervisor backend like Xen or KVM. When your unikernel is run, it starts much like a conventional OS does when run as a virtual machine, and so it must be passed references to devices such as the console, network interfaces and block devices on startup.

In general, a config.ml file is a normal OCaml module that calls register to register one or more jobs, each of which represent a process (with a start/stop lifecycle). Each job depends on some device drivers; all the available device drivers are defined in the Mirage module (see the Mirage module documentation).

In this case, this simple hello world example requires some notion of time, so we register a single job consisting of the Unikernel.Hello module (and, implicitly its start function) and pass it references to a timer.

When we call Mirage.main we specify the devices our Unikernel.Hello program depends on (a time device) and when we call Mirage.register, we provide instructions about how to satisfy those dependencies (it will be given a default_time device, suitable for the target it's eventually built for).

Building a Unix binary

Let's test all of this by first configuring, building, and running the resulting unikernel under Unix:

$ cd tutorial/hello
$ mirage configure -t unix

mirage configure generates a Makefile with all the build rules included from evaluating the configuration file and a mirage directory. The mirage directory includes generated files to run and build your program, including

a main.ml that represents the entry point of your unikernel,
and a hello-unix.opam file with a list of the packages necessary to build the unikernel.

Install the dependencies with

$ make depends

And build the unikernel with

$ make build

Our Unix binary is built as dist/hello. Note that make simply calls mirage build which itself turns into a simple dune build command. If you are familiar with dune it is possible to inspect the build rules for the unikernel generated in dune.build.

To run your application, execute the binary — and observe the exciting log messages that our loop is generating:

$ ./dist/hello

Building for Another Backend

Note: The following sections of this tutorial use the Solo5-based hvt backend as an example. This backend is supported on Linux, FreeBSD, and OpenBSD systems with hardware virtualization. Please see the Solo5 documentation for the support status of further backends such as spt (for deployment on Linux using a strict seccomp sandbox), virtio (for deployment on e.g. Google Compute Engine) and muen (for deployment on the Muen Separation Kernel). On supported platforms, Solo5 will be installed automatically when make depends is run.

To build a Solo5-based unikernel that will run on a host system with hardware virtualization, re-run mirage configure and ask for the hvt target instead of unix.

$ mirage configure -t hvt
$ make depends
$ make build

Everything else remains the same! The set of dependencies required to build, the generated main.ml, and the generated Makefile have changed, but since the source code of your application was parameterised over the Time module, it doesn't matter — you do not need to make any changes for your code to run when linked against the Solo5 console driver instead of Unix.

When you build the hvt version, you'll see a new artifact in the dist directory: a file called hello.hvt. Additionally, a solo5-hvt binary will be installed by OPAM on your $PATH. This binary is a tender, responsible for loading your unikernel, attaching to host system devices and running it. To try running hello.hvt, pass it as an argument to solo5-hvt:

$ solo5-hvt dist/hello.hvt
            |      ___|
  __|  _ \\  |  _ \\ __ \\
\\__ \\ (   | | (   |  ) |
____/\\___/ _|\\___/____/
Solo5: Memory map: 512 MB addressable:
Solo5:     unused @ (0x0 - 0xfffff)
Solo5:       text @ (0x100000 - 0x1e8fff)
Solo5:     rodata @ (0x1e9000 - 0x220fff)
Solo5:       data @ (0x221000 - 0x2d0fff)
Solo5:       heap >= 0x2d1000 < stack < 0x20000000
2018-06-21 12:16:28 -00:00: INF [application] hello
2018-06-21 12:16:29 -00:00: INF [application] hello
2018-06-21 12:16:30 -00:00: INF [application] hello
2018-06-21 12:16:31 -00:00: INF [application] hello
Solo5: solo5_exit(0) called

We get some additional output from the initialization of the unikernel and its successful boot, then we see our expected output, and Solo5's report of the application's successful completion.

Configuration Keys

It's very common to pass additional runtime information to a program via command-line options or arguments. But a unikernel doesn't have access to a command line, so how can we pass it runtime information?

Mirage provides a nice abstraction for this in the form of configuration keys. The Mirage module provides a module Key, which contains functions for creating and using configuration keys. For an example, let's have a look at hello-key:

$ cd tutorial/hello-key
$ cat config.ml
open Mirage

let hello =
  let doc = Key.Arg.info ~doc:"How to say hello." ["hello"] in
  Key.(create "hello" Arg.(opt string "Hello World!" doc))

let main =
  main
    ~keys:[key hello]
    ~packages:[package "duration"]
    "Unikernel.Hello" (time @-> job)

let () =
  register "hello" [main $ default_time]

We create a key with Key.create which is an optional bit of configuration. It will default to "Hello World!" if unspecified. This particular key happens to be of type string, so no conversion will be required, but it's possible to ask for more exotic types in the call to Arg. See the Functoria Key.Arg module documentation for more details.

Once we've created our configuration key, we specify that we'd like it available in the unikernel by passing it to main in the keys parameter.

We can then read the value corresponding to configuration key using the appropriate function in the generated Key_gen module. In our case, Key_gen.hello as shown below.

$ cat unikernel.ml
open Lwt.Infix

module Hello (Time : Mirage_time_lwt.S) = struct

  let start _time =

    let hello = Key_gen.hello () in

    let rec loop = function
      | 0 -> Lwt.return_unit
      | n ->
        Logs.info (fun f -> f "%s" hello);
        Time.sleep_ns (Duration.of_sec 1) >>= fun () ->
        loop (n-1)
    in
    loop 4

end

Let's configure the example for Unix and build it:

$ mirage configure -t unix
$ make depends
$ make build

When the target is Unix, Mirage will use an implementation for configuration keys that looks at the contents of OS.Env.argv. In other words, it looks directly at the command line that was used to invoke the program. If we call hello with no arguments, the default value is used:

$ dist/hello
2017-02-08 18:18:23 -03:00: INF [application] Hello World!
2017-02-08 18:18:24 -03:00: INF [application] Hello World!
2017-02-08 18:18:25 -03:00: INF [application] Hello World!
2017-02-08 18:18:26 -03:00: INF [application] Hello World!

but we can ask for something else:

$ dist/hello --hello="Bonjour!"
2017-02-08 18:20:46 +09:00: INF [application] Bonjour!
2017-02-08 18:20:47 +09:00: INF [application] Bonjour!
2017-02-08 18:20:48 +09:00: INF [application] Bonjour!
2017-02-08 18:20:49 +09:00: INF [application] Bonjour!

When the target is Unix, it's also possible to get useful hints by calling the generated program with --help.

Many configuration keys can be specified either at configuration time or at run time. mirage configure will allow us to change the default value for hello, while retaining the ability to override it at runtime:

$ mirage configure -t unix --hello="Hola!"
$ make depend
$ make
$ dist/hello
2017-02-08 18:30:30 +06:00: INF [application] Hola!
2017-02-08 18:30:31 +06:00: INF [application] Hola!
2017-02-08 18:30:32 +06:00: INF [application] Hola!
2017-02-08 18:30:33 +06:00: INF [application] Hola!
$ dist/hello --hello="Hi!"
2017-02-08 18:30:54 +06:00: INF [application] Hi!
2017-02-08 18:30:55 +06:00: INF [application] Hi!
2017-02-08 18:30:56 +06:00: INF [application] Hi!
2017-02-08 18:30:57 +06:00: INF [application] Hi!

When configured for non-Unix backends, other mechanisms are used to pass the runtime information to the unikernel. solo5-hvt, which we used to run hello.hvt in the non-keyed example, will pass keys specified on the command line to the unikernel when invoked:

$ cd tutorial/hello-key
$ mirage configure -t hvt
$ make depend
$ make
$ solo5-hvt -- dist/hello.hvt --hello="Hola!"
            |      ___|
  __|  _ \\  |  _ \\ __ \\
\\__ \\ (   | | (   |  ) |
____/\\___/ _|\\___/____/
Solo5: Memory map: 512 MB addressable:
Solo5:     unused @ (0x0 - 0xfffff)
Solo5:       text @ (0x100000 - 0x1e8fff)
Solo5:     rodata @ (0x1e9000 - 0x220fff)
Solo5:       data @ (0x221000 - 0x2d1fff)
Solo5:       heap >= 0x2d2000 < stack < 0x20000000
2018-06-21 12:18:03 -00:00: INF [application] Hola!
2018-06-21 12:18:04 -00:00: INF [application] Hola!
2018-06-21 12:18:05 -00:00: INF [application] Hola!
2018-06-21 12:18:06 -00:00: INF [application] Hola!
Solo5: solo5_exit(0) called

Step 2: Getting a block device

Most useful unikernels will need to obtain data from the outside world, so we'll explain this subsystem next.

Sector-addressible block devices

The device-usage/block/ directory in mirage-skeleton contains an example of attaching a raw block device to your unikernel. The Mirage_block interface signature contains the operations that are possible on a block device: primarily reading and writing aligned buffers to a 64-bit offset within the device. On Unix, the development workflow to handle block devices is by mapping them onto local files. On solo5 on the other hand, the block devices are mapped to alphanumeric names.

The solo5 tender then at runtime maps the names onto local files. The config.ml for the block example contains some logic for handling this difference. The expression if_impl Key.is_solo5 (block_of_file "storage") (block_of_file "disk.img") detects if we are on the solo5 target. If so, we emit a block device backed by the name storage. Otherwise, we emit a block device backed by the file disk.img. Remember, the name has to be alphanumeric on Solo5, so the dot in disk.img will not work on Solo5.

open Mirage

let main = main "Unikernel.Main" (block @-> job)

let img =
  if_impl Key.is_solo5 (block_of_file "storage") (block_of_file "disk.img")

let () = register "block_test" [main $ img]

The main binding looks much like the earlier hello example, except for the addition of a block device in the list..

As an aside, if you have your editor configured with OCaml mode, you should be able to see the inferred types for some of the variables in the configuration file. The @-> and $ combinators are designed such that any mismatches in the declared device driver types and the concrete registered implementations will result in a type error at configuration time.

Build this on Unix in the same way as the previous examples:

$ cd device-usage/block
$ mirage configure -t unix
$ make depends
$ make build

Now, with the unikernel built we can run it. However, the unikernel expects a block device. We can create a disk image of all zeroes before we run the unikernel:

$ dd if=/dev/zero of=disk.img count=100000 # only needed once
$ ./dist/block_test

block_test will write a series of patterns to the block device and read them back to check that they are the same (the logic for this is in unikernel.ml within the Block_test module).

We can build this example for another backend too:

$ mirage configure -t hvt
$ make depends
$ make build

Now we just need to boot the unikernel with solo5-hvt as before. We should see the same output after the VM boot preamble, but now MirageOS is linked against the Solo5 block device driver and is mapping the unikernel's block requests directly through to it, rather than relying on the host OS (the Linux or FreeBSD kernel).

If we tell solo5-hvt where the disk image for the name storage is, it will provide that disk image to the unikernel:

$ solo5-hvt --block:storage=disk.img ./dist/block_test.hvt
            |      ___|
  __|  _ \\  |  _ \\ __ \\
\\__ \\ (   | | (   |  ) |
____/\\___/ _|\\___/____/
Solo5: Bindings version v0.7.5
Solo5: Memory map: 512 MB addressable:
Solo5:   reserved @ (0x0 - 0xfffff)
Solo5:       text @ (0x100000 - 0x1defff)
Solo5:     rodata @ (0x1df000 - 0x214fff)
Solo5:       data @ (0x215000 - 0x2c1fff)
Solo5:       heap >= 0x2c2000 < stack < 0x20000000
2023-06-27 10:27:24 -00:00: INF [block] { Mirage_block.read_write = true; sector_size = 512;
              size_sectors = 100000L }
reading 1 sectors at 100000
reading 12 sectors at 99989
2023-06-27 10:27:24 -00:00: INF [block] Test sequence finished

2023-06-27 10:27:24 -00:00: INF [block] Total tests started: 10

2023-06-27 10:27:24 -00:00: INF [block] Total tests passed:  10

2023-06-27 10:27:24 -00:00: INF [block] Total tests failed:  0

Solo5: solo5_exit(0) called

Step 3: Key/value stores

The earlier block device example shows how very low-level access can work. Now let's move up to a more familiar abstraction: a key/value store that can retrieve buffers from string keys. This is essential for many common uses such as retrieving configuration data or website HTML and images.

The device-usage/kv_ro directory in mirage-skeleton contains a simple key/value store example. The subdirectory t/ contains a few files, one of which the unikernel will compare against a known constant.

The config.ml might look familiar after the earlier block and console examples:

open Mirage

let disk = generic_kv_ro "t"

let main =
  main
    "Unikernel.Main" (kv_ro @-> job)

let () =
  register "kv_ro" [main $ disk]

We construct the kv_ro device disk by using the generic_kv_ro function. This takes a single directory as its argument, and will do its best to provide the content of that directory to the unikernel by whatever means make sense given the target provided at configuration time. The best choice might be an implementation that calls functions from OCaml's Unix module (referred to as direct by the mirage tool), or perhaps a function that transforms an entire directory into a static ML file that can expose the file contents directly from memory (called crunch). crunch removes the need to have an external block device entirely and is very convenient indeed for small files.

Using generic_kv_ro in your config.ml causes Mirage to automatically create a configuration key, kv_ro, which you can use to request a specific implementation of the key-value store's implementation. To see documentation, try:

$ cd device-usage/kv_ro
$ mirage help configure

Under the "UNIKERNEL PARAMETERS" section, you should see:

       --kv_ro=KV_RO (absent=crunch)
           Use a fat, archive, crunch or direct pass-through implementation
           for the unikernel.

More documentation is available at the Mirage module documentation for generic_kv_ro.

Let's try a few different kinds of key-value implementations. First, we'll build a Unix version. If we don't specify which kind of kv_ro we want, we'll get a crunch implementation, the contents of which we can see at _build/default/static_t.ml, the file being generated by dune rules described in dune.build:

$ cd device-usage/kv_ro
$ mirage configure -t unix
$ make depends
$ make build
$ less _build/default/static_t.ml # the generated filesystem
$ dist/kv_ro

We can use the direct implementation with the Unix target as well:

$ cd device-usage/kv_ro
$ mirage configure -t unix --kv_ro=direct
$ make depends
$ make build
$ dist/kv_ro

You may have noticed that, unlike with our hello_key example, the kv_ro key can't be specified at runtime — it's only understood as an argument to mirage configure. This is because the kv_ro implementation we choose influences the set of dependencies that are assembled and baked into the final product. If we choose direct, we'll get a different set of software than if we choose crunch. In either case, no code that isn't required will be included in the final product.

You should now be seeing the power of the MirageOS configuration tool: We have built several applications that use fairly complex concepts such as filesystems and block devices that are independent of the implementations (by virtue of our application logic being a functor), and then are able to assemble several combinations of unikernels via relatively simple configuration files and options passed at compile time and runtime.

Step 4: Networking

There are several ways that we might want to configure our network for a Mirage application:

On Unix, it's convenient to use the standard kernel socket API for developing higher level protocols (such as HTTP). These run over TCP or UDP and so sockets work just fine.
When we want finer control over the network stack, or simply to test the fully-OCaml network implementation , we can use a userspace device facility such as the common Unix tuntap to parse Ethernet frames from userspace. This requires additional configuration to assign IP addresses, and possibly configure a network bridge to let the unikernel talk to the outside world.
Once the unikernel works under Unix with the direct OCaml TCP/IP stack, recompiling it for a unikernel target like xen, hvt, or virtio shouldn't result in a change in behavior.

All of this can be manipulated via command-line arguments or environment variables, just as we configured the key-value store in the previous example. The example in the device-usage/network directory of mirage-skeleton is illustrative:

open Mirage

let port =
  let doc = Key.Arg.info ~doc:"The TCP port on which to listen for incoming connections." ["port"] in
  Key.(create "port" Arg.(opt int 8080 doc))

let main = main ~keys:[Key.abstract port] "Unikernel.Main" (stackv4 @-> job)

let stack = generic_stackv4 default_network

let () =
  register "network" [
    main $ stack
  ]

We have a custom configuration key defining which TCP port to listen for connections on. The network device is derived from default_network, a function provided by Mirage which will choose a reasonable default based on the target the user chooses to pass to mirage configure - just like the reasonable default provided by generic_kv_ro in the previous example.

generic_stackv4 attempts to build a sensible network stack on top of the physical interface given by default_network. There are quite a few configuration keys exposed when generic_stackv4 is given related to networking configuration. For a full list, try mirage help configure in the device-usage/network directory.

Unix / Socket networking

Let's get the network stack compiling using the standard Unix sockets APIs first.

$ cd device-usage/network
$ mirage configure -t unix --net socket
$ make depends
$ make build
$ dist/network

This Unix application is now listening on TCP port 8080, and will print to the console information about data received. Let's try talking to it using the commonly available netcat nc(1) utility. From a different console execute:

$ echo -n hello tcp world | nc -nw1 127.0.0.1 8080

You should see log messages documenting your connection from 127.0.0.1 in the console running dist/network. You may have noticed that some information that you may have expected to see after looking at unikernel.ml isn't being output. That's because we haven't specified the log level for dist/network, and it defaults to info. Some of the output for this application is sent with the log level set to debug, so to see it, we need to run dist/network with a higher log level for all logs:

$ dist/network -l "*:debug"

The program will then output the debug-level logs, which include the content of any messages it reads. Here's an example of what you might see:

$ dist/network -l "*:debug"
2017-02-10 17:23:24 +02:00: INF [tcpip-stack-socket] Manager: connect
2017-02-10 17:23:24 +02:00: INF [tcpip-stack-socket] Manager: configuring
2017-02-10 17:23:27 +02:00: INF [application] new tcp connection from IP 127.0.0.1 on port 36358
2017-02-10 17:23:27 +02:00: DBG [application] read: 15 bytes:
hello tcp world

Unix / MirageOS Stack with DHCP

Next, let's try using the direct MirageOS network stack. It will be necessary to run these programs with sudo or as the root user, as they need direct access to a network device. We won't be able to contact them via the loopback interface on 127.0.0.1 either — the stack will need to either obtain IP address information via DHCP, or it can be configured directly via the --ipv4 configuration key.

To configure via DHCP:

$ cd device-usage/network
$ mirage configure -t unix --dhcp true --net direct
$ make depends
$ make build
$ sudo dist/network -l "*:debug"

Hopefully, the application will successfully receive its network configuration. Once the program has completed the lease transaction, it will log the configuration information, and you'll be able to contact it as before via its own IP.

Unix / MirageOS Stack with static IP addresses

By default, if we do not use DHCP with a direct network stack, Mirage will configure the stack to use an address of 10.0.0.2. You can specify a different address with the --ipv4 configuration key. Depending on whether you've configured with -t macosx or -t unix, the logic for contacting the application from another terminal will be different.

For unix: Verify that you have an existing tap0 interface by reviewing $ sudo ip link show; if you do not, load the tuntap kernel module ($ sudo modprobe tun) and create a tap0 interface owned by you ($ sudo tunctl -u $USER -t tap0). Bring tap0 up using $ sudo ifconfig tap0 10.0.0.1 up, then:

$ cd device-usage/network
$ mirage configure -t unix --dhcp false --net direct
$ make depends
$ make build
$ sudo dist/network -l "*:debug"

For macosx:

(* TODO! *)

Now you should be able to ping the unikernel's interface:

$ ping 10.0.0.2
PING 10.0.0.2 (10.0.0.2) 56(84) bytes of data.
64 bytes from 10.0.0.2: icmp_seq=1 ttl=38 time=0.527 ms
64 bytes from 10.0.0.2: icmp_seq=2 ttl=38 time=0.367 ms
64 bytes from 10.0.0.2: icmp_seq=3 ttl=38 time=0.291 ms
^C
--- 10.0.0.2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2005ms
rtt min/avg/max/mdev = 0.291/0.395/0.527/0.098 ms

Finally, you can then execute the same nc(1) commands as before (modulo the target IP address of course!) to interact with the running unikernel:

$ echo -n hello tcp world | nc -nw1 10.0.0.2 8080

And you will see the same output in the unikernel's terminal:

read: 15 "hello tcp world"

Hvt

Let's make a network-enabled unikernel with hvt! The IP configuration should be similar to what you've set up in the previous examples, but instead of -t unix or -t macosx, build with a hvt target. If you need to specify a static IP address, remember that it should go at the end of the command in which you invoke solo5-hvt, just like the argument to hello in the hello-key example.

$ cd device-usage/network
$ mirage configure -t hvt --dhcp true # for environments where DHCP works
$ make depends
$ make build
$ solo5-hvt --net:service=tap100 -- dist/network.hvt --ipv4=10.0.0.10/24
            |      ___|
  __|  _ \\  |  _ \\ __ \\
\\__ \\ (   | | (   |  ) |
____/\\___/ _|\\___/____/
Solo5: Memory map: 512 MB addressable:
Solo5:     unused @ (0x0 - 0xfffff)
Solo5:       text @ (0x100000 - 0x213fff)
Solo5:     rodata @ (0x214000 - 0x255fff)
Solo5:       data @ (0x256000 - 0x331fff)
Solo5:       heap >= 0x332000 < stack < 0x20000000
2018-06-21 12:24:46 -00:00: INF [netif] Plugging into 0 with mac 3a:40:76:41:5d:b0
2018-06-21 12:24:46 -00:00: INF [ethif] Connected Ethernet interface 3a:40:76:41:5d:b0
2018-06-21 12:24:46 -00:00: INF [arpv4] Connected arpv4 device on 3a:40:76:41:5d:b0
2018-06-21 12:24:46 -00:00: INF [udp] UDP interface connected on 10.0.0.10
2018-06-21 12:24:46 -00:00: INF [tcpip-stack-direct] stack assembled: mac=3a:40:76:41:5d:b0,ip=10.0.0.10

See the Solo5 documentation on running Solo5-based unikernels for details on how to set up the tap100 interface used above for hvt networking.

What's Next?

There are a number of other examples in device-usage/ which show some simple invocations of various devices like consoles and clocks. You may also be interested in the applications/ directory of the mirage-skeleton repository, which contains examples that use multiple devices to build nontrivial applications, like DNS, DHCP, and HTTPS servers.

The real MirageOS website (which is itself a unikernel) may also be of interest to you! Documentation is available at mirage-www, and the source code is published in a public GitHub repository.