From b1de1da318631c6d29f6c04dea370f712078f443 Mon Sep 17 00:00:00 2001
From: Ting-Yu Wang <anivia@google.com>
Date: Thu, 7 Jan 2021 14:14:58 -0800
Subject: netstack: Refactor tcpip.Endpoint.Read

Read now takes a destination io.Writer, count, options. Keeping the method name
Read, in contrast to the Write method.

This enables:
* direct transfer of views under VV
* zero copy

It also eliminates the need for sentry to keep a slice of view because
userspace had requested a read that is smaller than the view returned, removing
the complexity there.

Read/Peek/ReadPacket are now consolidated together and some duplicate code is
removed.

PiperOrigin-RevId: 350636322
---
 pkg/tcpip/transport/packet/endpoint.go | 46 ++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 21 deletions(-)

(limited to 'pkg/tcpip/transport/packet')

diff --git a/pkg/tcpip/transport/packet/endpoint.go b/pkg/tcpip/transport/packet/endpoint.go
index e5e247342..3ab060751 100644
--- a/pkg/tcpip/transport/packet/endpoint.go
+++ b/pkg/tcpip/transport/packet/endpoint.go
@@ -26,6 +26,7 @@ package packet
 
 import (
 	"fmt"
+	"io"
 
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -160,8 +161,8 @@ func (ep *endpoint) Close() {
 // ModerateRecvBuf implements tcpip.Endpoint.ModerateRecvBuf.
 func (ep *endpoint) ModerateRecvBuf(copied int) {}
 
-// Read implements tcpip.PacketEndpoint.ReadPacket.
-func (ep *endpoint) ReadPacket(addr *tcpip.FullAddress, info *tcpip.LinkPacketInfo) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
+// Read implements tcpip.Endpoint.Read.
+func (ep *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
 	ep.rcvMu.Lock()
 
 	// If there's no data to read, return that read would block or that the
@@ -173,29 +174,37 @@ func (ep *endpoint) ReadPacket(addr *tcpip.FullAddress, info *tcpip.LinkPacketIn
 			err = tcpip.ErrClosedForReceive
 		}
 		ep.rcvMu.Unlock()
-		return buffer.View{}, tcpip.ControlMessages{}, err
+		return tcpip.ReadResult{}, err
 	}
 
 	packet := ep.rcvList.Front()
-	ep.rcvList.Remove(packet)
-	ep.rcvBufSize -= packet.data.Size()
+	if !opts.Peek {
+		ep.rcvList.Remove(packet)
+		ep.rcvBufSize -= packet.data.Size()
+	}
 
 	ep.rcvMu.Unlock()
 
-	if addr != nil {
-		*addr = packet.senderAddr
+	res := tcpip.ReadResult{
+		Total: packet.data.Size(),
+		ControlMessages: tcpip.ControlMessages{
+			HasTimestamp: true,
+			Timestamp:    packet.timestampNS,
+		},
 	}
-
-	if info != nil {
-		*info = packet.packetInfo
+	if opts.NeedRemoteAddr {
+		res.RemoteAddr = packet.senderAddr
+	}
+	if opts.NeedLinkPacketInfo {
+		res.LinkPacketInfo = packet.packetInfo
 	}
 
-	return packet.data.ToView(), tcpip.ControlMessages{HasTimestamp: true, Timestamp: packet.timestampNS}, nil
-}
-
-// Read implements tcpip.Endpoint.Read.
-func (ep *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
-	return ep.ReadPacket(addr, nil)
+	n, err := packet.data.ReadTo(dst, count, opts.Peek)
+	if n == 0 && err != nil {
+		return res, tcpip.ErrBadBuffer
+	}
+	res.Count = n
+	return res, nil
 }
 
 func (*endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-chan struct{}, *tcpip.Error) {
@@ -203,11 +212,6 @@ func (*endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-cha
 	return 0, nil, tcpip.ErrInvalidOptionValue
 }
 
-// Peek implements tcpip.Endpoint.Peek.
-func (*endpoint) Peek([][]byte) (int64, *tcpip.Error) {
-	return 0, nil
-}
-
 // Disconnect implements tcpip.Endpoint.Disconnect. Packet sockets cannot be
 // disconnected, and this function always returns tpcip.ErrNotSupported.
 func (*endpoint) Disconnect() *tcpip.Error {
-- 
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