Pass DNS addresses from en0 interface to guest instance

qemu user-mode networking is forwarding DNS to just a single
DNS entry from the host. So if that entry does not resolve
the query, there is no fallback.

Signed-off-by: Jan Dubois <[email protected]>

Author: jandubois

pkg/cidata/cidata.TEMPLATE.d/boot/15-setup-dns.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+set -eux
+
+DNS=""
+# NOTE: Busybox sh does not support `for ((i=0;i<$N;i++))` form
+for f in $(seq 0 $((LIMA_CIDATA_DNS - 1))); do
+	dnsaddressvar="LIMA_CIDATA_DNS_${f}_ADDRESS"
+	dnsaddress="$(eval echo \$"$dnsaddressvar")"
+	if [ -z "${DNS}" ]; then
+		DNS="${dnsaddress}"
+	else
+		DNS="${DNS} ${dnsaddress}"
+	fi
+	echo "nameserver ${dnsaddress}" >>/etc/resolv.conf
+done
+
+if [ -n "${DNS}" ]; then
+	RESOLVED=/etc/systemd/resolved.conf
+	if [ -f "${RESOLVED}" ]; then
+		sed -i "/DNS=/d" "${RESOLVED}"
+		sed -i "/\[Resolve\]/a DNS=${DNS}" "${RESOLVED}"
+		systemctl restart systemd-resolved.service
+	fi
+
+	UDHCPC=/usr/share/udhcpc/default.script
+	if [ -f "${UDHCPC}" ]; then
+		sed -i "/export dns/a dns=\"${DNS}\"" "${UDHCPC}"
+	fi
+fi

pkg/cidata/cidata.TEMPLATE.d/lima.env

@@ -4,6 +4,10 @@ LIMA_CIDATA_MOUNTS={{ len .Mounts }}
 {{- range $i, $val := .Mounts}}
 LIMA_CIDATA_MOUNTS_{{$i}}_MOUNTPOINT={{$val}}
 {{- end}}
+LIMA_CIDATA_DNS={{ len .DNSAddresses }}
+{{- range $i, $val := .DNSAddresses }}
+LIMA_CIDATA_DNS_{{$i}}_ADDRESS={{$val}}
+{{- end}}
 {{- if .Containerd.User}}
 LIMA_CIDATA_CONTAINERD_USER=1
 {{- else}}

pkg/cidata/cidata.go

@@ -16,6 +16,7 @@ import (
 	"github.com/lima-vm/lima/pkg/iso9660util"
 	"github.com/lima-vm/lima/pkg/limayaml"
 	"github.com/lima-vm/lima/pkg/localpathutil"
+	"github.com/lima-vm/lima/pkg/osutil"
 	"github.com/lima-vm/lima/pkg/qemu/qemuconst"
 	"github.com/lima-vm/lima/pkg/sshutil"
 	"github.com/lima-vm/lima/pkg/store/filenames"
@@ -79,6 +80,11 @@ func GenerateISO9660(instDir, name string, y *limayaml.LimaYAML) error {
 		args.Networks = append(args.Networks, Network{MACAddress: vde.MACAddress, Name: vde.Name})
 	}
 
+	args.DNSAddresses, err = osutil.DNSAddresses()
+	if err != nil {
+		return err
+	}
+
 	if err := ValidateTemplateArgs(args); err != nil {
 		return err
 	}

pkg/cidata/template.go

@@ -36,6 +36,7 @@ type TemplateArgs struct {
 	Containerd   Containerd
 	Networks     []Network
 	SlirpGateway string
+	DNSAddresses []string
 }
 
 func ValidateTemplateArgs(args TemplateArgs) error {

pkg/osutil/dns_darwin.go

@@ -0,0 +1,25 @@
+package osutil
+
+import "github.com/lima-vm/lima/pkg/sysprof"
+
+func DNSAddresses() ([]string, error) {
+	nwData, err := sysprof.NetworkData()
+	if err != nil {
+		return nil, err
+	}
+	var addresses []string
+	if len(nwData) > 0 {
+		// Return DNS addresses from en0 interface
+		for _, nw := range nwData {
+			if nw.Interface == "en0" {
+				addresses = nw.DNS.ServerAddresses
+				break
+			}
+		}
+		// In case "en0" is not found, use the addresses of the first interface
+		if len(addresses) == 0 {
+			addresses = nwData[0].DNS.ServerAddresses
+		}
+	}
+	return addresses, nil
+}

pkg/osutil/dns_others.go

@@ -0,0 +1,8 @@
+// +build !darwin
+
+package osutil
+
+func DNSAddresses() ([]string, error) {
+	// TODO: parse /etc/resolv.conf?
+	return []string{}, nil
+}

pkg/sysprof/network_darwin.go

@@ -0,0 +1,14 @@
+package sysprof
+
+type SPNetworkDataType struct {
+	SPNetworkDataType []NetworkDataType `json:"SPNetworkDataType"`
+}
+
+type NetworkDataType struct {
+	DNS       DNS    `json:"DNS"`
+	Interface string `json:"interface"`
+}
+
+type DNS struct {
+	ServerAddresses []string `json:"ServerAddresses"`
+}

pkg/sysprof/sysprof_darwin.go

@@ -0,0 +1,37 @@
+package sysprof
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"os/exec"
+	"sync"
+)
+
+var (
+	networkDataOnce   sync.Once
+	networkDataCached SPNetworkDataType
+	networkDataError  error
+)
+
+func NetworkData() ([]NetworkDataType, error) {
+	networkDataOnce.Do(func() {
+		jsonBytes, networkDataError := SystemProfiler("SPNetworkDataType")
+		if networkDataError == nil {
+			networkDataError = json.Unmarshal(jsonBytes, &networkDataCached)
+		}
+	})
+	return networkDataCached.SPNetworkDataType, networkDataError
+}
+
+func SystemProfiler(dataType string) ([]byte, error) {
+	var stdout, stderr bytes.Buffer
+	cmd := exec.Command("system_profiler", dataType, "-json")
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		return nil, fmt.Errorf("failed to run %v: stdout=%q, stderr=%q: %w",
+			cmd.Args, stdout.String(), stderr.String(), err)
+	}
+	return stdout.Bytes(), nil
+}