Migrate to PacketHeader API for PacketBuffer.

Formerly, when a packet is constructed or parsed, all headers are set by the
client code. This almost always involved prepending to pk.Header buffer or
trimming pk.Data portion. This is known to prone to bugs, due to the complexity
and number of the invariants assumed across netstack to maintain.

In the new PacketHeader API, client will call Push()/Consume() method to
construct/parse an outgoing/incoming packet. All invariants, such as slicing
and trimming, are maintained by the API itself.

NewPacketBuffer() is introduced to create new PacketBuffer. Zero value is no
longer valid.

PacketBuffer now assumes the packet is a concatenation of following portions:
* LinkHeader
* NetworkHeader
* TransportHeader
* Data
Any of them could be empty, or zero-length.

PiperOrigin-RevId: 326507688

1 files changed, 9 insertions, 5 deletions

diff --git a/pkg/tcpip/link/sharedmem/tx.go b/pkg/tcpip/link/sharedmem/tx.go
index 6b8d7859d..44f421c2d 100644
--- a/pkg/tcpip/link/sharedmem/tx.go
+++ b/pkg/tcpip/link/sharedmem/tx.go
@@ -18,6 +18,7 @@ import (
 	"math"
 	"syscall"
 
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/link/sharedmem/queue"
 )
 
@@ -76,9 +77,9 @@ func (t *tx) cleanup() {
 	syscall.Munmap(t.data)
 }
 
-// transmit sends a packet made up of up to two buffers. Returns a boolean that
-// specifies whether the packet was successfully transmitted.
-func (t *tx) transmit(a, b []byte) bool {
+// transmit sends a packet made of bufs. Returns a boolean that specifies
+// whether the packet was successfully transmitted.
+func (t *tx) transmit(bufs ...buffer.View) bool {
 	// Pull completions from the tx queue and add their buffers back to the
 	// pool so that we can reuse them.
 	for {
@@ -93,7 +94,10 @@ func (t *tx) transmit(a, b []byte) bool {
 	}
 
 	bSize := t.bufs.entrySize
-	total := uint32(len(a) + len(b))
+	total := uint32(0)
+	for _, data := range bufs {
+		total += uint32(len(data))
+	}
 	bufCount := (total + bSize - 1) / bSize
 
 	// Allocate enough buffers to hold all the data.
@@ -115,7 +119,7 @@ func (t *tx) transmit(a, b []byte) bool {
 	// Copy data into allocated buffers.
 	nBuf := buf
 	var dBuf []byte
-	for _, data := range [][]byte{a, b} {
+	for _, data := range bufs {
 		for len(data) > 0 {
 			if len(dBuf) == 0 {
 				dBuf = t.data[nBuf.Offset:][:nBuf.Size]