go-libvirt-plain/README.md

libvirt

Package go-libvirt provides a pure Go interface for interacting with libvirt.

Rather than using libvirt's C bindings, this package makes use of libvirt's RPC interface, as documented here. Connections to the libvirt server may be local, or remote. RPC packets are encoded using the XDR standard as defined by RFC 4506.

libvirt's RPC interface is quite extensive, and changes from one version to the next, so this project uses a code generator to build the go bindings. The code generator should be run whenever you want to build go-libvirt for a new version of libvirt. To do this, you'll need to set an environment variable LIBVIRT_SOURCE to the directory containing the untarred libvirt sources, and then run go generate ./... from the go-libvirt directory. The code generator consumes src/remote/remote_protocol.x and produces go bindings for all the remote procedures defined there.

Pull requests are welcome!

How to Use This Library

Once you've vendored go-libvirt into your project, you'll probably want to call some libvirt functions. There's some example code below showing how to connect to libvirt and make one such call, but once you get past the introduction you'll next want to call some other libvirt functions. How do you find them?

Start with the libvirt API reference. Let's say you want to gracefully shutdown a VM, and after reading through the libvirt docs you determine that virDomainShutdown() is the function you want to call to do that. Where's that function in go-libvirt? We transform the names slightly when building the go bindings. There's no need for a global prefix like "vir" in Go, since all our functions are inside the package namespace, so we drop it. That means the Go function for virDomainShutdown() is just DomainShutdown(), and sure enough, you can find the Go function DomainShutdown() in libvirt.gen.go, with parameters and return values equivalent to those documented in the API reference.

Suppose you then decide you need more control over your shutdown, so you switch over to virDomainShutdownFlags(). As its name suggests, this function takes a flag parameter which has possible values specified in an enum called virDomainShutdownFlagValues. Flag types like this are a little tricky for the code generator, because the C functions just take an integer type - only the libvirt documentation actually ties the flags to the enum types. In most cases though we're able to generate a wrapper function with a distinct flag type, making it easier for Go tooling to suggest possible flag values while you're working. Checking the documentation for this function:

godoc github.com/digitalocean/go-libvirt DomainShutdownFlags

returns this:

func (l *Libvirt) DomainShutdownFlags(Dom Domain, Flags DomainShutdownFlagValues) (err error)

If you want to see the possible flag values, godoc can help again:

$ godoc github.com/digitalocean/go-libvirt DomainShutdownFlagValues

type DomainShutdownFlagValues int32
    DomainShutdownFlagValues as declared in libvirt/libvirt-domain.h:1121

const (
    DomainShutdownDefault      DomainShutdownFlagValues = iota
    DomainShutdownAcpiPowerBtn DomainShutdownFlagValues = 1
    DomainShutdownGuestAgent   DomainShutdownFlagValues = 2
    DomainShutdownInitctl      DomainShutdownFlagValues = 4
    DomainShutdownSignal       DomainShutdownFlagValues = 8
    DomainShutdownParavirt     DomainShutdownFlagValues = 16
)
    DomainShutdownFlagValues enumeration from libvirt/libvirt-domain.h:1121

One other suggestion: most of the code in go-libvirt is now generated, but a few hand-written routines still exist in libvirt.go, and wrap calls to the generated code with slightly different parameters or return values. We suggest avoiding these hand-written routines and calling the generated routines in libvirt.gen.go instead. Over time these handwritten routines will be removed from go-libvirt.

Warning

The libvirt project strongly recommends against talking to the RPC interface directly. They consider it to be a private implementation detail with the possibility of being entirely rearchitected in the future.

While these package are reasonably well-tested and have seen some use inside of DigitalOcean, there may be subtle bugs which could cause the packages to act in unexpected ways. Use at your own risk!

In addition, the API is not considered stable at this time. If you would like to include package libvirt in a project, we highly recommend vendoring it into your project.

Example

package main

import (
	"fmt"
	"log"
	"net"
	"time"

	"github.com/digitalocean/go-libvirt"
)

func main() {
	// This dials libvirt on the local machine, but you can substitute the first
	// two parameters with "tcp", "<ip address>:<port>" to connect to libvirt on
	// a remote machine.
	c, err := net.DialTimeout("unix", "/var/run/libvirt/libvirt-sock", 2*time.Second)
	if err != nil {
		log.Fatalf("failed to dial libvirt: %v", err)
	}

	l := libvirt.New(c)
	if err := l.Connect(); err != nil {
		log.Fatalf("failed to connect: %v", err)
	}

	v, err := l.Version()
	if err != nil {
		log.Fatalf("failed to retrieve libvirt version: %v", err)
	}
	fmt.Println("Version:", v)

	domains, err := l.Domains()
	if err != nil {
		log.Fatalf("failed to retrieve domains: %v", err)
	}

	fmt.Println("ID\tName\t\tUUID")
	fmt.Printf("--------------------------------------------------------\n")
	for _, d := range domains {
		fmt.Printf("%d\t%s\t%x\n", d.ID, d.Name, d.UUID)
	}

	if err := l.Disconnect(); err != nil {
		log.Fatal("failed to disconnect: %v", err)
	}
}

Version: 1.3.4
ID	Name		UUID
--------------------------------------------------------
1	Test-1		dc329f87d4de47198cfd2e21c6105b01
2	Test-2		dc229f87d4de47198cfd2e21c6105b01