Fix handling of the resolv.conf

Leverage what is it passed from the daemon
Fix check about the host networking

Signed-off-by: Flavio Crisciani <flavio.crisciani@docker.com>

libnetwork/libnetwork_linux_test.go

@@ -658,6 +658,7 @@ func TestResolvConfHost(t *testing.T) {
 	defer os.Remove(resolvConfPath)
 
 	sb, err := controller.NewSandbox(containerID,
+		libnetwork.OptionUseDefaultSandbox(),
 		libnetwork.OptionResolvConfPath(resolvConfPath),
 		libnetwork.OptionOriginResolvConfPath("/etc/resolv.conf"))
 	if err != nil {

libnetwork/osl/kernel/knobs.go

@@ -2,7 +2,7 @@ package kernel
 
 type conditionalCheck func(val1, val2 string) bool
 
-// OSValue represents a tuple, value defired, check function when to apply the value
+// OSValue represents a tuple, value defined, check function when to apply the value
 type OSValue struct {
 	Value   string
 	CheckFn conditionalCheck

libnetwork/resolvconf/resolvconf.go

@@ -14,6 +14,11 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
+const (
+	// DefaultResolvConf points to the default file used for dns configuration on a linux machine
+	DefaultResolvConf = "/etc/resolv.conf"
+)
+
 var (
 	// Note: the default IPv4 & IPv6 resolvers are set to Google's Public DNS
 	defaultIPv4Dns = []string{"nameserver 8.8.8.8", "nameserver 8.8.4.4"}
@@ -50,15 +55,7 @@ type File struct {
 
 // Get returns the contents of /etc/resolv.conf and its hash
 func Get() (*File, error) {
-	resolv, err := ioutil.ReadFile("/etc/resolv.conf")
-	if err != nil {
-		return nil, err
-	}
-	hash, err := ioutils.HashData(bytes.NewReader(resolv))
-	if err != nil {
-		return nil, err
-	}
-	return &File{Content: resolv, Hash: hash}, nil
+	return GetSpecific(DefaultResolvConf)
 }
 
 // GetSpecific returns the contents of the user specified resolv.conf file and its hash

libnetwork/sandbox.go

@@ -1098,8 +1098,8 @@ func OptionDNSOptions(options string) SandboxOption {
 	}
 }
 
-// OptionUseDefaultSandbox function returns an option setter for using default sandbox to
-// be passed to container Create method.
+// OptionUseDefaultSandbox function returns an option setter for using default sandbox
+// (host namespace) to be passed to container Create method.
 func OptionUseDefaultSandbox() SandboxOption {
 	return func(sb *sandbox) {
 		sb.config.useDefaultSandBox = true

libnetwork/sandbox_dns_unix.go

@@ -81,7 +81,9 @@ func (sb *sandbox) buildHostsFile() error {
 	}
 
 	// This is for the host mode networking
-	if sb.config.originHostsPath != "" {
+	if sb.config.useDefaultSandBox && len(sb.config.extraHosts) == 0 {
+		// We are working under the assumption that the origin file option had been properly expressed by the upper layer
+		// if not here we are going to error out
 		if err := copyFile(sb.config.originHostsPath, sb.config.hostsPath); err != nil && !os.IsNotExist(err) {
 			return types.InternalErrorf("could not copy source hosts file %s to %s: %v", sb.config.originHostsPath, sb.config.hostsPath, err)
 		}
@@ -190,8 +192,13 @@ func (sb *sandbox) setupDNS() error {
 		return err
 	}
 
-	// This is for the host mode networking
-	if sb.config.originResolvConfPath != "" {
+	// When the user specify a conainter in the host namespace and do no have any dns option specified
+	// we just copy the host resolv.conf from the host itself
+	if sb.config.useDefaultSandBox &&
+		len(sb.config.dnsList) == 0 && len(sb.config.dnsSearchList) == 0 && len(sb.config.dnsOptionsList) == 0 {
+
+		// We are working under the assumption that the origin file option had been properly expressed by the upper layer
+		// if not here we are going to error out
 		if err := copyFile(sb.config.originResolvConfPath, sb.config.resolvConfPath); err != nil {
 			if !os.IsNotExist(err) {
 				return fmt.Errorf("could not copy source resolv.conf file %s to %s: %v", sb.config.originResolvConfPath, sb.config.resolvConfPath, err)
@@ -204,7 +211,12 @@ func (sb *sandbox) setupDNS() error {
 		return nil
 	}
 
-	currRC, err := resolvconf.Get()
+	originResolvConfPath := sb.config.originResolvConfPath
+	if originResolvConfPath == "" {
+		// if not specified fallback to default /etc/resolv.conf
+		originResolvConfPath = resolvconf.DefaultResolvConf
+	}
+	currRC, err := resolvconf.GetSpecific(originResolvConfPath)
 	if err != nil {
 		if !os.IsNotExist(err) {
 			return err
@@ -271,7 +283,7 @@ func (sb *sandbox) updateDNS(ipv6Enabled bool) error {
 	)
 
 	// This is for the host mode networking
-	if sb.config.originResolvConfPath != "" {
+	if sb.config.useDefaultSandBox {
 		return nil
 	}