Discover IP address of the network cards attached to a LAN

When a network card is attached to a LAN the `domain.ListAllInterfaceAddresses`
API cannot be used to get the IP address associated with the interfaces.

The only solution to this problem is to use the [Qemu guest agent](http://wiki.libvirt.org/page/Qemu_guest_agent)
to fetch this information.

This PR will take advantage of the qemu guest ageint (when installed
inside of the domain) to workaround the limitations of the
`domain.ListAllInterfaceAddresses`.

In theory this PR could also allow to relax the required version of
libvirt.

Signed-off-by: Flavio Castelli <fcastelli@suse.com>

1 files changed, 90 insertions, 0 deletions

diff --git a/libvirt/qemu_agent.go b/libvirt/qemu_agent.go
new file mode 100644
index 00000000..10bf45cc
--- /dev/null
+++ b/libvirt/qemu_agent.go
@@ -0,0 +1,90 @@
+package libvirt
+
+import (
+	"encoding/json"
+	"log"
+	"strings"
+
+	libvirt "github.com/dmacvicar/libvirt-go"
+)
+
+type QemuAgentInterfacesResponse struct {
+	Interfaces []QemuAgentInterface `json:"return"`
+}
+
+type QemuAgentInterface struct {
+	Name        string `json:"name"`
+	Hwaddr      string `json:"hardware-address"`
+	IpAddresses []struct {
+		Type    string `json:"ip-address-type"`
+		Address string `json:"ip-address"`
+		Prefix  uint   `json:"prefix"`
+	} `json:"ip-addresses"`
+}
+
+// Retrieve all the interfaces attached to a domain and their addresses. Only
+// the interfaces with at least an IP address are returned.
+// When wait4ipv4 is turned on the code will not report interfaces that don't
+// have a ipv4 address set. This is useful when a domain gets the ipv6 address
+// before the ipv4 one.
+func getDomainInterfacesViaQemuAgent(domain *libvirt.VirDomain, wait4ipv4 bool) []libvirt.VirDomainInterface {
+	log.Print("[DEBUG] get network interfaces using qemu agent")
+
+	var interfaces []libvirt.VirDomainInterface
+
+	result := domain.QemuAgentCommand(
+		"{\"execute\":\"guest-network-get-interfaces\"}",
+		libvirt.VIR_DOMAIN_QEMU_AGENT_COMMAND_DEFAULT,
+		0)
+
+	log.Printf("[DEBUG] qemu-agent response: %s", result)
+
+	response := QemuAgentInterfacesResponse{}
+	if err := json.Unmarshal([]byte(result), &response); err != nil {
+		log.Printf("[DEBUG] Error converting Qemu agent response about domain interfaces: %s", err)
+		log.Printf("[DEBUG] Original message: %s", response)
+		log.Print("[DEBUG] Returning an empty list of interfaces")
+		return interfaces
+	}
+	log.Printf("[DEBUG] Parsed response %+v", response)
+
+	for _, iface := range response.Interfaces {
+		if iface.Name == "lo" {
+			// ignore loopback interface
+			continue
+		}
+
+		libVirtIface := libvirt.VirDomainInterface{}
+		libVirtIface.Name = iface.Name
+		libVirtIface.Hwaddr = iface.Hwaddr
+
+		ipv4Assigned := false
+		for _, addr := range iface.IpAddresses {
+			if addr.Address == "" {
+				// ignore interfaces without an address (eg. waiting for dhcp lease)
+				continue
+			}
+
+			libVirtAddr := libvirt.VirDomainIPAddress{}
+			libVirtAddr.Addr = addr.Address
+			libVirtAddr.Prefix = addr.Prefix
+			switch strings.ToLower(addr.Type) {
+			case "ipv4":
+				libVirtAddr.Type = libvirt.VIR_IP_ADDR_TYPE_IPV4
+				ipv4Assigned = true
+			case "ipv6":
+				libVirtAddr.Type = libvirt.VIR_IP_ADDR_TYPE_IPV6
+			default:
+				log.Printf("[ERROR] Cannot handle unknown address type %s", addr.Type)
+			}
+			libVirtIface.Addrs = append(libVirtIface.Addrs, libVirtAddr)
+		}
+		if len(libVirtIface.Addrs) > 0 && (ipv4Assigned || !wait4ipv4) {
+			interfaces = append(interfaces, libVirtIface)
+		}
+	}
+
+	log.Printf("[DEBUG] Interfaces obtained via qemu Agent: %+v", interfaces)
+
+	return interfaces
+}