10 files changed, 84 insertions, 3 deletions
diff --git a/pkg/tcpip/link/channel/channel.go b/pkg/tcpip/link/channel/channel.go
index cebc34553..3f5440cc1 100644
--- a/pkg/tcpip/link/channel/channel.go
+++ b/pkg/tcpip/link/channel/channel.go
@@ -67,6 +67,11 @@ func (e *Endpoint) Attach(dispatcher stack.NetworkDispatcher) {
 	e.dispatcher = dispatcher
 }
 
+// IsAttached implements stack.LinkEndpoint.IsAttached.
+func (e *Endpoint) IsAttached() bool {
+	return e.dispatcher != nil
+}
+
 // MTU implements stack.LinkEndpoint.MTU. It returns the value initialized
 // during construction.
 func (e *Endpoint) MTU() uint32 {
diff --git a/pkg/tcpip/link/fdbased/endpoint.go b/pkg/tcpip/link/fdbased/endpoint.go
index da74cd644..668514454 100644
--- a/pkg/tcpip/link/fdbased/endpoint.go
+++ b/pkg/tcpip/link/fdbased/endpoint.go
@@ -45,9 +45,10 @@ type endpoint struct {
 	// its end of the communication pipe.
 	closed func(*tcpip.Error)
 
-	vv     *buffer.VectorisedView
-	iovecs []syscall.Iovec
-	views  []buffer.View
+	vv       *buffer.VectorisedView
+	iovecs   []syscall.Iovec
+	views    []buffer.View
+	attached bool
 }
 
 // Options specify the details about the fd-based endpoint to be created.
@@ -96,9 +97,15 @@ func New(opts *Options) tcpip.LinkEndpointID {
 // Attach launches the goroutine that reads packets from the file descriptor and
 // dispatches them via the provided dispatcher.
 func (e *endpoint) Attach(dispatcher stack.NetworkDispatcher) {
+	e.attached = true
 	go e.dispatchLoop(dispatcher) // S/R-FIXME
 }
 
+// IsAttached implements stack.LinkEndpoint.IsAttached.
+func (e *endpoint) IsAttached() bool {
+	return e.attached
+}
+
 // MTU implements stack.LinkEndpoint.MTU. It returns the value initialized
 // during construction.
 func (e *endpoint) MTU() uint32 {
diff --git a/pkg/tcpip/link/loopback/loopback.go b/pkg/tcpip/link/loopback/loopback.go
index 1a9cd09d7..f38847949 100644
--- a/pkg/tcpip/link/loopback/loopback.go
+++ b/pkg/tcpip/link/loopback/loopback.go
@@ -32,6 +32,11 @@ func (e *endpoint) Attach(dispatcher stack.NetworkDispatcher) {
 	e.dispatcher = dispatcher
 }
 
+// IsAttached implements stack.LinkEndpoint.IsAttached.
+func (e *endpoint) IsAttached() bool {
+	return e.dispatcher != nil
+}
+
 // MTU implements stack.LinkEndpoint.MTU. It returns a constant that matches the
 // linux loopback interface.
 func (*endpoint) MTU() uint32 {
diff --git a/pkg/tcpip/link/sharedmem/sharedmem.go b/pkg/tcpip/link/sharedmem/sharedmem.go
index 2c0f1b294..5369ebc68 100644
--- a/pkg/tcpip/link/sharedmem/sharedmem.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem.go
@@ -137,6 +137,13 @@ func (e *endpoint) Attach(dispatcher stack.NetworkDispatcher) {
 	e.mu.Unlock()
 }
 
+// IsAttached implements stack.LinkEndpoint.IsAttached.
+func (e *endpoint) IsAttached() bool {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	return e.workerStarted
+}
+
 // MTU implements stack.LinkEndpoint.MTU. It returns the value initialized
 // during construction.
 func (e *endpoint) MTU() uint32 {
diff --git a/pkg/tcpip/link/sniffer/sniffer.go b/pkg/tcpip/link/sniffer/sniffer.go
index 72d9a0f1c..3a40081c0 100644
--- a/pkg/tcpip/link/sniffer/sniffer.go
+++ b/pkg/tcpip/link/sniffer/sniffer.go
@@ -143,6 +143,11 @@ func (e *endpoint) Attach(dispatcher stack.NetworkDispatcher) {
 	e.lower.Attach(e)
 }
 
+// IsAttached implements stack.LinkEndpoint.IsAttached.
+func (e *endpoint) IsAttached() bool {
+	return e.dispatcher != nil
+}
+
 // MTU implements stack.LinkEndpoint.MTU. It just forwards the request to the
 // lower endpoint.
 func (e *endpoint) MTU() uint32 {
diff --git a/pkg/tcpip/link/waitable/waitable.go b/pkg/tcpip/link/waitable/waitable.go
index 2c6e73f22..91aed7a12 100644
--- a/pkg/tcpip/link/waitable/waitable.go
+++ b/pkg/tcpip/link/waitable/waitable.go
@@ -58,6 +58,11 @@ func (e *Endpoint) Attach(dispatcher stack.NetworkDispatcher) {
 	e.lower.Attach(e)
 }
 
+// IsAttached implements stack.LinkEndpoint.IsAttached.
+func (e *Endpoint) IsAttached() bool {
+	return e.dispatcher != nil
+}
+
 // MTU implements stack.LinkEndpoint.MTU. It just forwards the request to the
 // lower endpoint.
 func (e *Endpoint) MTU() uint32 {
diff --git a/pkg/tcpip/link/waitable/waitable_test.go b/pkg/tcpip/link/waitable/waitable_test.go
index cb433dc19..188049322 100644
--- a/pkg/tcpip/link/waitable/waitable_test.go
+++ b/pkg/tcpip/link/waitable/waitable_test.go
@@ -34,6 +34,11 @@ func (e *countedEndpoint) Attach(dispatcher stack.NetworkDispatcher) {
 	e.dispatcher = dispatcher
 }
 
+// IsAttached implements stack.LinkEndpoint.IsAttached.
+func (e *countedEndpoint) IsAttached() bool {
+	return e.dispatcher != nil
+}
+
 func (e *countedEndpoint) MTU() uint32 {
 	return e.mtu
 }
diff --git a/pkg/tcpip/network/ip_test.go b/pkg/tcpip/network/ip_test.go
index 797501858..c5f8714da 100644
--- a/pkg/tcpip/network/ip_test.go
+++ b/pkg/tcpip/network/ip_test.go
@@ -90,6 +90,11 @@ func (t *testObject) DeliverTransportControlPacket(local, remote tcpip.Address,
 // Attach is only implemented to satisfy the LinkEndpoint interface.
 func (*testObject) Attach(stack.NetworkDispatcher) {}
 
+// IsAttached implements stack.LinkEndpoint.IsAttached.
+func (*testObject) IsAttached() bool {
+	return true
+}
+
 // MTU implements stack.LinkEndpoint.MTU. It just returns a constant that
 // matches the linux loopback MTU.
 func (*testObject) MTU() uint32 {
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index e7e6381ac..15b2418ad 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -224,6 +224,10 @@ type LinkEndpoint interface {
 	// Attach attaches the data link layer endpoint to the network-layer
 	// dispatcher of the stack.
 	Attach(dispatcher NetworkDispatcher)
+
+	// IsAttached returns whether a NetworkDispatcher is attached to the
+	// endpoint.
+	IsAttached() bool
 }
 
 // A LinkAddressResolver is an extension to a NetworkProtocol that
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index f0fbd8aad..3976f585c 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -541,6 +541,39 @@ func (s *Stack) NICInfo() map[tcpip.NICID]NICInfo {
 	return nics
 }
 
+// NICStateFlags holds information about the state of an NIC.
+type NICStateFlags struct {
+	// Up indicates whether the interface is running.
+	Up bool
+
+	// Running indicates whether resources are allocated.
+	Running bool
+
+	// Promiscuous indicates whether the interface is in promiscuous mode.
+	Promiscuous bool
+}
+
+// NICFlags returns flags about the state of the NIC. It returns an error if
+// the NIC corresponding to id cannot be found.
+func (s *Stack) NICFlags(id tcpip.NICID) (NICStateFlags, *tcpip.Error) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	nic := s.nics[id]
+	if nic == nil {
+		return NICStateFlags{}, tcpip.ErrUnknownNICID
+	}
+
+	ret := NICStateFlags{
+		// Netstack interfaces are always up.
+		Up: true,
+
+		Running:     nic.linkEP.IsAttached(),
+		Promiscuous: nic.promiscuous,
+	}
+	return ret, nil
+}
+
 // AddAddress adds a new network-layer address to the specified NIC.
 func (s *Stack) AddAddress(id tcpip.NICID, protocol tcpip.NetworkProtocolNumber, addr tcpip.Address) *tcpip.Error {
 	s.mu.RLock()