Use opaque types to represent time

Introduce tcpip.MonotonicTime; replace int64 in tcpip.Clock method
returns with time.Time and MonotonicTime to improve type safety and
ensure that monotonic clock readings are never compared to wall clock
readings.

PiperOrigin-RevId: 375775907

2 files changed, 17 insertions, 5 deletions

diff --git a/pkg/tcpip/transport/packet/endpoint.go b/pkg/tcpip/transport/packet/endpoint.go
index fa703a0ed..cd8c99d41 100644
--- a/pkg/tcpip/transport/packet/endpoint.go
+++ b/pkg/tcpip/transport/packet/endpoint.go
@@ -27,6 +27,7 @@ package packet
 import (
 	"fmt"
 	"io"
+	"time"
 
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -41,9 +42,8 @@ type packet struct {
 	packetEntry
 	// data holds the actual packet data, including any headers and
 	// payload.
-	data buffer.VectorisedView `state:".(buffer.VectorisedView)"`
-	// timestampNS is the unix time at which the packet was received.
-	timestampNS int64
+	data       buffer.VectorisedView `state:".(buffer.VectorisedView)"`
+	receivedAt time.Time             `state:".(int64)"`
 	// senderAddr is the network address of the sender.
 	senderAddr tcpip.FullAddress
 	// packetInfo holds additional information like the protocol
@@ -189,7 +189,7 @@ func (ep *endpoint) Read(dst io.Writer, opts tcpip.ReadOptions) (tcpip.ReadResul
 		Total: packet.data.Size(),
 		ControlMessages: tcpip.ControlMessages{
 			HasTimestamp: true,
-			Timestamp:    packet.timestampNS,
+			Timestamp:    packet.receivedAt.UnixNano(),
 		},
 	}
 	if opts.NeedRemoteAddr {
@@ -451,7 +451,7 @@ func (ep *endpoint) HandlePacket(nicID tcpip.NICID, localAddr tcpip.LinkAddress,
 			packet.data = buffer.NewVectorisedView(pkt.Size(), pkt.Views())
 		}
 	}
-	packet.timestampNS = ep.stack.Clock().NowNanoseconds()
+	packet.receivedAt = ep.stack.Clock().Now()
 
 	ep.rcvList.PushBack(&packet)
 	ep.rcvBufSize += packet.data.Size()
diff --git a/pkg/tcpip/transport/packet/endpoint_state.go b/pkg/tcpip/transport/packet/endpoint_state.go
index 5bd860d20..e729921db 100644
--- a/pkg/tcpip/transport/packet/endpoint_state.go
+++ b/pkg/tcpip/transport/packet/endpoint_state.go
@@ -15,11 +15,23 @@
 package packet
 
 import (
+	"time"
+
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )
 
+// saveReceivedAt is invoked by stateify.
+func (p *packet) saveReceivedAt() int64 {
+	return p.receivedAt.UnixNano()
+}
+
+// loadReceivedAt is invoked by stateify.
+func (p *packet) loadReceivedAt(nsec int64) {
+	p.receivedAt = time.Unix(0, nsec)
+}
+
 // saveData saves packet.data field.
 func (p *packet) saveData() buffer.VectorisedView {
 	// We cannot save p.data directly as p.data.views may alias to p.views,