net/dns: remove PerDomain from Config.

It's currently unused, and no longer makes sense with the upcoming
DNS infrastructure. Keep it in tailcfg for now, since we need protocol
compat for a bit longer.

Signed-off-by: David Anderson <danderson@tailscale.com>

ipn/ipnlocal/local.go

@@ -1452,7 +1452,6 @@ func (b *LocalBackend) authReconfig() {
 		rcfg.DNS = dns.Config{
 			Nameservers: nm.DNS.Nameservers,
 			Domains:     nm.DNS.Domains,
-			PerDomain:   nm.DNS.PerDomain,
 			Proxied:     proxied,
 		}
 	}

net/dns/config.go

@@ -17,11 +17,6 @@ type Config struct {
 	Nameservers []netaddr.IP
 	// Domains are the search domains to use.
 	Domains []string
-	// PerDomain indicates whether it is preferred to use Nameservers
-	// only for DNS queries for subdomains of Domains.
-	// Note that Nameservers may still be applied to all queries
-	// if the manager does not support per-domain settings.
-	PerDomain bool
 	// Proxied indicates whether DNS requests are proxied through a dns.Resolver.
 	// This enables MagicDNS.
 	Proxied bool
@@ -30,7 +25,7 @@ type Config struct {
 // Equal determines whether its argument and receiver
 // represent equivalent DNS configurations (then DNS reconfig is a no-op).
 func (lhs Config) Equal(rhs Config) bool {
-	if lhs.Proxied != rhs.Proxied || lhs.PerDomain != rhs.PerDomain {
+	if lhs.Proxied != rhs.Proxied {
 		return false
 	}
 
@@ -71,7 +66,4 @@ type ManagerConfig struct {
 	// Cleanup indicates that the manager is created for cleanup only.
 	// A no-op manager will be instantiated if the system needs no cleanup.
 	Cleanup bool
-	// PerDomain indicates that a manager capable of per-domain configuration is preferred.
-	// Certain managers are per-domain only; they will not be considered if this is false.
-	PerDomain bool
 }

net/dns/manager.go

@@ -45,10 +45,8 @@ type Manager struct {
 func NewManager(mconfig ManagerConfig) *Manager {
 	mconfig.Logf = logger.WithPrefix(mconfig.Logf, "dns: ")
 	m := &Manager{
-		logf: mconfig.Logf,
+		logf:    mconfig.Logf,
-		impl: newManager(mconfig),
+		impl:    newManager(mconfig),
-
-		config:  Config{PerDomain: mconfig.PerDomain},
 		mconfig: mconfig,
 	}
 
@@ -72,16 +70,6 @@ func (m *Manager) Set(config Config) error {
 		return err
 	}
 
-	// Switching to and from per-domain mode may require a change of manager.
-	if config.PerDomain != m.config.PerDomain {
-		if err := m.impl.Down(); err != nil {
-			return err
-		}
-		m.mconfig.PerDomain = config.PerDomain
-		m.impl = newManager(m.mconfig)
-		m.logf("switched to %T", m.impl)
-	}
-
 	err := m.impl.Up(config)
 	// If we save the config, we will not retry next time. Only do this on success.
 	if err == nil {

net/dns/manager_linux.go

@@ -6,8 +6,7 @@ package dns
 
 func newManager(mconfig ManagerConfig) managerImpl {
 	switch {
-	// systemd-resolved should only activate per-domain.
+	case isResolvedActive():
-	case isResolvedActive() && mconfig.PerDomain:
 		if mconfig.Cleanup {
 			return newNoopManager(mconfig)
 		} else {

tailcfg/tailcfg.go

@@ -769,13 +769,12 @@ type DNSConfig struct {
 	Nameservers []netaddr.IP `json:",omitempty"`
 	// Domains are the search domains to use.
 	Domains []string `json:",omitempty"`
-	// PerDomain indicates whether it is preferred to use Nameservers
+	// PerDomain is not set by the control server, and does nothing.
-	// only for DNS queries for subdomains of Domains.
+	// TODO(danderson): revise DNS configuration to make this useful
-	// Some OSes and OS configurations don't support per-domain DNS configuration,
+	// again.
-	// in which case Nameservers applies to all DNS requests regardless of PerDomain's value.
 	PerDomain bool
 	// Proxied indicates whether DNS requests are proxied through a dns.Resolver.
-	// This enables MagicDNS. It is togglable independently of PerDomain.
+	// This enables MagicDNS.
 	Proxied bool
 }