Allow clients to store an opaque NICContext with NICs

...retrievable later via stack.NICInfo().

Clients of this library can use it to add metadata that should be tracked
alongside a NIC, to avoid having to keep a map[tcpip.NICID]metadata mirroring
stack.Stack's nic map.

PiperOrigin-RevId: 288924900

pkg/tcpip/stack/nic.go

@@ -27,10 +27,11 @@ import (
 // NIC represents a "network interface card" to which the networking stack is
 // attached.
 type NIC struct {
-	stack  *Stack
-	id     tcpip.NICID
-	name   string
-	linkEP LinkEndpoint
+	stack   *Stack
+	id      tcpip.NICID
+	name    string
+	linkEP  LinkEndpoint
+	context NICContext
 
 	mu            sync.RWMutex
 	spoofing      bool
@@ -84,7 +85,7 @@ const (
 )
 
 // newNIC returns a new NIC using the default NDP configurations from stack.
-func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint) *NIC {
+func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, ctx NICContext) *NIC {
 	// TODO(b/141011931): Validate a LinkEndpoint (ep) is valid. For
 	// example, make sure that the link address it provides is a valid
 	// unicast ethernet address.
@@ -98,6 +99,7 @@ func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint) *NIC {
 		id:         id,
 		name:       name,
 		linkEP:     ep,
+		context:    ctx,
 		primary:    make(map[tcpip.NetworkProtocolNumber][]*referencedNetworkEndpoint),
 		endpoints:  make(map[NetworkEndpointID]*referencedNetworkEndpoint),
 		mcastJoins: make(map[NetworkEndpointID]int32),

pkg/tcpip/stack/stack.go

@@ -796,6 +796,9 @@ func (s *Stack) NewPacketEndpoint(cooked bool, netProto tcpip.NetworkProtocolNum
 	return s.rawFactory.NewPacketEndpoint(s, cooked, netProto, waiterQueue)
 }
 
+// NICContext is an opaque pointer used to store client-supplied NIC metadata.
+type NICContext interface{}
+
 // NICOptions specifies the configuration of a NIC as it is being created.
 // The zero value creates an enabled, unnamed NIC.
 type NICOptions struct {
@@ -805,6 +808,12 @@ type NICOptions struct {
 	// Disabled specifies whether to avoid calling Attach on the passed
 	// LinkEndpoint.
 	Disabled bool
+
+	// Context specifies user-defined data that will be returned in stack.NICInfo
+	// for the NIC. Clients of this library can use it to add metadata that
+	// should be tracked alongside a NIC, to avoid having to keep a
+	// map[tcpip.NICID]metadata mirroring stack.Stack's nic map.
+	Context NICContext
 }
 
 // CreateNICWithOptions creates a NIC with the provided id, LinkEndpoint, and
@@ -819,7 +828,7 @@ func (s *Stack) CreateNICWithOptions(id tcpip.NICID, ep LinkEndpoint, opts NICOp
 		return tcpip.ErrDuplicateNICID
 	}
 
-	n := newNIC(s, id, opts.Name, ep)
+	n := newNIC(s, id, opts.Name, ep, opts.Context)
 
 	s.nics[id] = n
 	if !opts.Disabled {
@@ -886,6 +895,10 @@ type NICInfo struct {
 	MTU uint32
 
 	Stats NICStats
+
+	// Context is user-supplied data optionally supplied in CreateNICWithOptions.
+	// See type NICOptions for more details.
+	Context NICContext
 }
 
 // NICInfo returns a map of NICIDs to their associated information.
@@ -908,6 +921,7 @@ func (s *Stack) NICInfo() map[tcpip.NICID]NICInfo {
 			Flags:             flags,
 			MTU:               nic.linkEP.MTU(),
 			Stats:             nic.stats,
+			Context:           nic.context,
 		}
 	}
 	return nics

pkg/tcpip/stack/stack_test.go

@@ -2001,6 +2001,46 @@ func TestNICAutoGenAddr(t *testing.T) {
 	}
 }
 
+// TestNICContextPreservation tests that you can read out via stack.NICInfo the
+// Context data you pass via NICContext.Context in stack.CreateNICWithOptions.
+func TestNICContextPreservation(t *testing.T) {
+	var ctx *int
+	tests := []struct {
+		name string
+		opts stack.NICOptions
+		want stack.NICContext
+	}{
+		{
+			"context_set",
+			stack.NICOptions{Context: ctx},
+			ctx,
+		},
+		{
+			"context_not_set",
+			stack.NICOptions{},
+			nil,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			s := stack.New(stack.Options{})
+			id := tcpip.NICID(1)
+			ep := channel.New(0, 0, tcpip.LinkAddress("\x00\x00\x00\x00\x00\x00"))
+			if err := s.CreateNICWithOptions(id, ep, test.opts); err != nil {
+				t.Fatalf("got stack.CreateNICWithOptions(%d, %+v, %+v) = %s, want nil", id, ep, test.opts, err)
+			}
+			nicinfos := s.NICInfo()
+			nicinfo, ok := nicinfos[id]
+			if !ok {
+				t.Fatalf("got nicinfos[%d] = _, %t, want _, true; nicinfos = %+v", id, ok, nicinfos)
+			}
+			if got, want := nicinfo.Context == test.want, true; got != want {
+				t.Fatal("got nicinfo.Context == ctx = %t, want %t; nicinfo.Context = %p, ctx = %p", got, want, nicinfo.Context, test.want)
+			}
+		})
+	}
+}
+
 // TestNICAutoGenAddrWithOpaque tests the auto-generation of IPv6 link-local
 // addresses with opaque interface identifiers. Link Local addresses should
 // always be generated with opaque IIDs if configured to use them, even if the