Refactor software GSO code.

Software GSO implementation currently has a complicated code path with
implicit assumptions that all packets to WritePackets carry same Data
and it does this to avoid allocations on the path etc. But this makes it
hard to reuse the WritePackets API.

This change breaks all such assumptions by introducing a new Vectorised
View API ReadToVV which can be used to cleanly split a VV into multiple
independent VVs. Further this change also makes packet buffers linkable
to form an intrusive list. This allows us to get rid of the array of
packet buffers that are passed in the WritePackets API call and replace
it with a list of packet buffers.

While this code does introduce some more allocations in the benchmarks
it doesn't cause any degradation.

Updates #231

PiperOrigin-RevId: 304731742

1 files changed, 4 insertions, 10 deletions

diff --git a/pkg/tcpip/stack/packet_buffer.go b/pkg/tcpip/stack/packet_buffer.go
index 9367de180..dc125f25e 100644
--- a/pkg/tcpip/stack/packet_buffer.go
+++ b/pkg/tcpip/stack/packet_buffer.go
@@ -23,9 +23,11 @@ import (
 // As a PacketBuffer traverses up the stack, it may be necessary to pass it to
 // multiple endpoints. Clone() should be called in such cases so that
 // modifications to the Data field do not affect other copies.
-//
-// +stateify savable
 type PacketBuffer struct {
+	// PacketBufferEntry is used to build an intrusive list of
+	// PacketBuffers.
+	PacketBufferEntry
+
 	// Data holds the payload of the packet. For inbound packets, it also
 	// holds the headers, which are consumed as the packet moves up the
 	// stack. Headers are guaranteed not to be split across views.
@@ -34,14 +36,6 @@ type PacketBuffer struct {
 	// or otherwise modified.
 	Data buffer.VectorisedView
 
-	// DataOffset is used for GSO output. It is the offset into the Data
-	// field where the payload of this packet starts.
-	DataOffset int
-
-	// DataSize is used for GSO output. It is the size of this packet's
-	// payload.
-	DataSize int
-
 	// Header holds the headers of outbound packets. As a packet is passed
 	// down the stack, each layer adds to Header.
 	Header buffer.Prependable