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

9 files changed, 53 insertions, 54 deletions

diff --git a/pkg/tcpip/stack/BUILD b/pkg/tcpip/stack/BUILD
index 8d80e9cee..5e963a4af 100644
--- a/pkg/tcpip/stack/BUILD
+++ b/pkg/tcpip/stack/BUILD
@@ -15,6 +15,18 @@ go_template_instance(
     },
 )
 
+go_template_instance(
+    name = "packet_buffer_list",
+    out = "packet_buffer_list.go",
+    package = "stack",
+    prefix = "PacketBuffer",
+    template = "//pkg/ilist:generic_list",
+    types = {
+        "Element": "*PacketBuffer",
+        "Linker": "*PacketBuffer",
+    },
+)
+
 go_library(
     name = "stack",
     srcs = [
@@ -29,7 +41,7 @@ go_library(
         "ndp.go",
         "nic.go",
         "packet_buffer.go",
-        "packet_buffer_state.go",
+        "packet_buffer_list.go",
         "rand.go",
         "registration.go",
         "route.go",
diff --git a/pkg/tcpip/stack/forwarder_test.go b/pkg/tcpip/stack/forwarder_test.go
index c45c43d21..e9c652042 100644
--- a/pkg/tcpip/stack/forwarder_test.go
+++ b/pkg/tcpip/stack/forwarder_test.go
@@ -101,7 +101,7 @@ func (f *fwdTestNetworkEndpoint) WritePacket(r *Route, gso *GSO, params NetworkH
 }
 
 // WritePackets implements LinkEndpoint.WritePackets.
-func (f *fwdTestNetworkEndpoint) WritePackets(r *Route, gso *GSO, pkts []PacketBuffer, params NetworkHeaderParams) (int, *tcpip.Error) {
+func (f *fwdTestNetworkEndpoint) WritePackets(r *Route, gso *GSO, pkts PacketBufferList, params NetworkHeaderParams) (int, *tcpip.Error) {
 	panic("not implemented")
 }
 
@@ -260,10 +260,10 @@ func (e fwdTestLinkEndpoint) WritePacket(r *Route, gso *GSO, protocol tcpip.Netw
 }
 
 // WritePackets stores outbound packets into the channel.
-func (e *fwdTestLinkEndpoint) WritePackets(r *Route, gso *GSO, pkts []PacketBuffer, protocol tcpip.NetworkProtocolNumber) (int, *tcpip.Error) {
+func (e *fwdTestLinkEndpoint) WritePackets(r *Route, gso *GSO, pkts PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, *tcpip.Error) {
 	n := 0
-	for _, pkt := range pkts {
-		e.WritePacket(r, gso, protocol, pkt)
+	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
+		e.WritePacket(r, gso, protocol, *pkt)
 		n++
 	}
 
diff --git a/pkg/tcpip/stack/iptables.go b/pkg/tcpip/stack/iptables.go
index 37907ae24..6c0a4b24d 100644
--- a/pkg/tcpip/stack/iptables.go
+++ b/pkg/tcpip/stack/iptables.go
@@ -209,6 +209,23 @@ func (it *IPTables) Check(hook Hook, pkt PacketBuffer) bool {
 	return true
 }
 
+// CheckPackets runs pkts through the rules for hook and returns a map of packets that
+// should not go forward.
+//
+// NOTE: unlike the Check API the returned map contains packets that should be
+// dropped.
+func (it *IPTables) CheckPackets(hook Hook, pkts PacketBufferList) (drop map[*PacketBuffer]struct{}) {
+	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
+		if ok := it.Check(hook, *pkt); !ok {
+			if drop == nil {
+				drop = make(map[*PacketBuffer]struct{})
+			}
+			drop[pkt] = struct{}{}
+		}
+	}
+	return drop
+}
+
 // Precondition: pkt.NetworkHeader is set.
 func (it *IPTables) checkChain(hook Hook, pkt PacketBuffer, table Table, ruleIdx int) chainVerdict {
 	// Start from ruleIdx and walk the list of rules until a rule gives us
diff --git a/pkg/tcpip/stack/ndp_test.go b/pkg/tcpip/stack/ndp_test.go
index 598468bdd..27dc8baf9 100644
--- a/pkg/tcpip/stack/ndp_test.go
+++ b/pkg/tcpip/stack/ndp_test.go
@@ -468,7 +468,7 @@ func TestDADResolve(t *testing.T) {
 				// As per RFC 4861 section 4.3, a possible option is the Source Link
 				// Layer option, but this option MUST NOT be included when the source
 				// address of the packet is the unspecified address.
-				checker.IPv6(t, p.Pkt.Header.View().ToVectorisedView().First(),
+				checker.IPv6(t, p.Pkt.Header.View(),
 					checker.SrcAddr(header.IPv6Any),
 					checker.DstAddr(snmc),
 					checker.TTL(header.NDPHopLimit),
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
diff --git a/pkg/tcpip/stack/packet_buffer_state.go b/pkg/tcpip/stack/packet_buffer_state.go
deleted file mode 100644
index 0c6b7924c..000000000
--- a/pkg/tcpip/stack/packet_buffer_state.go
+++ /dev/null
@@ -1,27 +0,0 @@
-// Copyright 2019 The gVisor Authors.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package stack
-
-import "gvisor.dev/gvisor/pkg/tcpip/buffer"
-
-// beforeSave is invoked by stateify.
-func (pk *PacketBuffer) beforeSave() {
-	// Non-Data fields may be slices of the Data field. This causes
-	// problems for SR, so during save we make each header independent.
-	pk.Header = pk.Header.DeepCopy()
-	pk.LinkHeader = append(buffer.View(nil), pk.LinkHeader...)
-	pk.NetworkHeader = append(buffer.View(nil), pk.NetworkHeader...)
-	pk.TransportHeader = append(buffer.View(nil), pk.TransportHeader...)
-}
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index ac043b722..23ca9ee03 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -246,7 +246,7 @@ type NetworkEndpoint interface {
 
 	// WritePackets writes packets to the given destination address and
 	// protocol. pkts must not be zero length.
-	WritePackets(r *Route, gso *GSO, pkts []PacketBuffer, params NetworkHeaderParams) (int, *tcpip.Error)
+	WritePackets(r *Route, gso *GSO, pkts PacketBufferList, params NetworkHeaderParams) (int, *tcpip.Error)
 
 	// WriteHeaderIncludedPacket writes a packet that includes a network
 	// header to the given destination address.
@@ -393,7 +393,7 @@ type LinkEndpoint interface {
 	// Right now, WritePackets is used only when the software segmentation
 	// offload is enabled. If it will be used for something else, it may
 	// require to change syscall filters.
-	WritePackets(r *Route, gso *GSO, pkts []PacketBuffer, protocol tcpip.NetworkProtocolNumber) (int, *tcpip.Error)
+	WritePackets(r *Route, gso *GSO, pkts PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, *tcpip.Error)
 
 	// WriteRawPacket writes a packet directly to the link. The packet
 	// should already have an ethernet header.
diff --git a/pkg/tcpip/stack/route.go b/pkg/tcpip/stack/route.go
index 9fbe8a411..a0e5e0300 100644
--- a/pkg/tcpip/stack/route.go
+++ b/pkg/tcpip/stack/route.go
@@ -168,23 +168,26 @@ func (r *Route) WritePacket(gso *GSO, params NetworkHeaderParams, pkt PacketBuff
 	return err
 }
 
-// WritePackets writes the set of packets through the given route.
-func (r *Route) WritePackets(gso *GSO, pkts []PacketBuffer, params NetworkHeaderParams) (int, *tcpip.Error) {
+// WritePackets writes a list of n packets through the given route and returns
+// the number of packets written.
+func (r *Route) WritePackets(gso *GSO, pkts PacketBufferList, params NetworkHeaderParams) (int, *tcpip.Error) {
 	if !r.ref.isValidForOutgoing() {
 		return 0, tcpip.ErrInvalidEndpointState
 	}
 
 	n, err := r.ref.ep.WritePackets(r, gso, pkts, params)
 	if err != nil {
-		r.Stats().IP.OutgoingPacketErrors.IncrementBy(uint64(len(pkts) - n))
+		r.Stats().IP.OutgoingPacketErrors.IncrementBy(uint64(pkts.Len() - n))
 	}
 	r.ref.nic.stats.Tx.Packets.IncrementBy(uint64(n))
-	payloadSize := 0
-	for i := 0; i < n; i++ {
-		r.ref.nic.stats.Tx.Bytes.IncrementBy(uint64(pkts[i].Header.UsedLength()))
-		payloadSize += pkts[i].DataSize
+
+	writtenBytes := 0
+	for i, pb := 0, pkts.Front(); i < n && pb != nil; i, pb = i+1, pb.Next() {
+		writtenBytes += pb.Header.UsedLength()
+		writtenBytes += pb.Data.Size()
 	}
-	r.ref.nic.stats.Tx.Bytes.IncrementBy(uint64(payloadSize))
+
+	r.ref.nic.stats.Tx.Bytes.IncrementBy(uint64(writtenBytes))
 	return n, err
 }
 
diff --git a/pkg/tcpip/stack/stack_test.go b/pkg/tcpip/stack/stack_test.go
index b8543b71e..3f8a2a095 100644
--- a/pkg/tcpip/stack/stack_test.go
+++ b/pkg/tcpip/stack/stack_test.go
@@ -153,7 +153,7 @@ func (f *fakeNetworkEndpoint) WritePacket(r *stack.Route, gso *stack.GSO, params
 }
 
 // WritePackets implements stack.LinkEndpoint.WritePackets.
-func (f *fakeNetworkEndpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts []stack.PacketBuffer, params stack.NetworkHeaderParams) (int, *tcpip.Error) {
+func (f *fakeNetworkEndpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.PacketBufferList, params stack.NetworkHeaderParams) (int, *tcpip.Error) {
 	panic("not implemented")
 }