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About Solo5

Solo5 is most useful as a "base layer" to run MirageOS and IncludeOS unikernels, either on various existing hypervisors (KVM/QEMU, bhyve) or on a specialized "unikernel monitor" called ukvm.

Quickstart

You can run a hello-world application like this:

$ make
$ ./tests/test_hello/ukvm-bin ./tests/test_hello/test_hello.ukvm

About ukvm

ukvm runs as a Linux process and uses KVM. The goal of ukvm is to be a small, modular monitor, in which its functionality and interfaces are customized to the unikernel that is being built. In other words, the unikernel monitor exhibits the characteristic of "only what is needed" for the unikernel to run. It has the potential to provide a thinner interface to the guest unikernel (thinner than either a container or a VM), a simpler I/O interface (e.g., packet send rather than virtio), and better performance due to its simplicity (e.g., fast boot). Check out our paper and presentation from USENIX HotCloud '16 for more information.

Building MirageOS unikernels with Solo5

Support for Solo5 as a target is integrated since the release of MirageOS 3.0, which adds two new targets to the mirage configure command:

1. ukvm: A specialized "unikernel monitor" which runs on Linux (x86_64 and arm64) and uses KVM directly via /dev/kvm.
2. virtio: An x86_64 system with virtio network and disk interfaces. Use this target for QEMU/KVM, plain QEMU, bhyve or other hypervisors (see below).

You can build for either of these targets using the standard MirageOS build process, which will output either a .ukvm or .virtio unikernel binary.

For the ukvm target, in addition to the .ukvm unikernel binary a ukvm-bin binary will be built. This is the ukvm monitor specialised for your unikernel.

Running Solo5 unikernels directly

The following examples use the standalone test_ping_serve unikernel which is built as part of the normal Solo5 build process.

test_ping_serve is a minimalist network test which will respond only to ARP and ICMP echo requests sent to the hard-coded IP address of 10.0.0.2. It accepts two possible command line arguments: Either verbose for verbose operation or limit to terminate after having sent 100,000 ICMP echo replies.

Setting up

By convention, we will use the tap100 interface to talk to the unikernel.

To set up the tap100 interface on Linux, run (as root):

ip tuntap add tap100 mode tap
ip addr add 10.0.0.1/24 dev tap100
ip link set dev tap100 up

To set up bhyve and the tap100 interface on FreeBSD, run (as root):

kldload vmm
kldload if_tap
kldload nmdm
sysctl -w net.link.tap.up_on_open=1
ifconfig tap100 create 10.0.0.1/24 link0 up

Running with ukvm on Linux

A specialized monitor called ukvm-bin is generated as part of the build process, so the command line arguments may differ depending on the needs of the unikernel. To see the arguments, run ukvm-bin with no arguments or --help.

To launch the unikernel:

./ukvm-bin --net=tap100 ./test_ping_serve.ukvm verbose

Use ^C to terminate the unikernel.

Running with KVM/QEMU on Linux, or bhyve on FreeBSD

To launch the unikernel:

solo5-run-virtio -n tap100 ./test_ping_serve.virtio verbose

Use ^C to terminate the unikernel.

The solo5-run-virtio script is automatically installed in your $PATH when using the solo5-kernel-virtio OPAM package as part of a MirageOS build environment. Using it is not required; by default it will print the commands used to setup and launch the guest VM. You can run these manually if desired.

Running virtio unikernels with other hypervisors

The virtio target produces a unikernel that uses the multiboot protocol for booting. If your hypervisor can boot a multiboot-compliant kernel directly then this is the preferred method.

If your hypervisor requires a full disk image to boot, you can use the solo5-mkimage tool to build one. This tool is automatically installed in your $PATH when using the solo5-kernel-virtio OPAM package as part of a MirageOS build environment.

solo5-mkimage supports the following image formats:

• raw: A raw disk image, written out as a sparse file.
• tar: A disk image suitable for uploading to Google Compute Engine.

The following devices are supported by the Solo5 virtio target:

• the serial console, fixed at COM1 and 115200 baud
• the KVM paravirtualized clock, if available
• a single virtio network device attached to the PCI bus
• a single virtio block device attached to the PCI bus

Note that Solo5 on virtio does not support ACPI power-off. This can manifest itself in delays shutting down Solo5 guests running on hypervisors which wait for the guest to respond to ACPI power-off before performing a hard shutdown.

Developing Solo5 and ukvm

If you'd like to develop Solo5, ukvm and/or investigate porting other unikernels to use Solo5 as a base layer, the public APIs are defined in kernel/solo5.h and ukvm/ukvm.h. These interfaces are still evolving and subject to change.

We also have some simple standalone unikernels written in C to test Solo5, see tests for these.

The coding style for this project is "as for the Linux kernel, but with 4 spaces instead of tabs".

The best place for Mirage-related discussions about Solo5 and/or ukvm is to post to the MirageOS-devel mailing list, with general Solo5/ukvm discussions on https://devel.unikernel.org/.

Debugging on ukvm

You can debug the unikernel running in ukvm using gdb, but need to build a ukvm-bin with gdb support. To do so, edit the Makefile (generated in the case of Mirage), and add gdb to the UKVM_MODULES make variable. Then, running make ukvm-bin should build a version with gdb support.

Start ukvm with the --gdb flag, like this:

$ cd tests/test_hello
$ ./ukvm-bin --gdb test_hello.ukvm

And then from another console start gdb and connect to the remote target listening at localhost:1234:

$ gdb --ex="target remote localhost:1234" test_hello.ukvm

Here is a typical gdb session:

(gdb) break puts
Breakpoint 1 at 0x100530: puts. (2 locations)
(gdb) c
Continuing.

Breakpoint 1, puts (s=s@entry=0x107808 "\n**** Solo5 standalone test_hello ****\n\n") at test_hello.c:25
25	{
(gdb) bt
#0  puts (s=s@entry=0x107808 "\n**** Solo5 standalone test_hello ****\n\n") at test_hello.c:25
#1  0x0000000000106a8e in solo5_app_main (cmdline=cmdline@entry=0x6000 "") at test_hello.c:31
#2  0x0000000000100089 in _start (arg=0x5000) at ukvm/kernel.c:42
(gdb) s
26	    solo5_console_write(s, strlen(s));
(gdb)